Development and evaluation of a signal analysis and a ...

Development and evaluation of a signal analysis and a readout system of straw tube detectors for the PANDA spectrometerDOCTORAL THESIS
Development and evaluation of a signal analysis and a readout system of straw tube
detectors for the PANDA spectrometer
Author: Pawe STRZEMPEK
Co-supervisor: Grzegorz KORCYL
Oswiadczenie
Ja nizej podpisany Pawe Strzempek doktorant Wydziau Fizyki, Astronomii i In- formatyki Stosowanej Uniwersytetu Jagiellonskiego oswiadczam, ze przedozona przeze mnie rozprawa doktorska pt. „ Development and evaluation of a signal analysis and a readout system of straw tube detectors for the PANDA spectrometer” jest oryginalna i przedstawia wyniki badan wykonanych przeze mnie osobiscie, pod kierunkiem prof. dr hab. Piotra Salabury. Prace napisaem samodzielnie.
Oswiadczam, ze moja rozprawa doktorska zostaa opracowana zgodnie z Ustawa o prawie autorskim i prawach pokrewnych z dnia 4 lutego 1994 r. (Dziennik Ustaw 1994 nr 24 poz. 83 wraz z pózniejszymi zmianami).
Jestem swiadom, ze niezgodnosc niniejszego oswiadczenia z prawda ujawniona w dowolnym czasie, niezaleznie od skutków prawnych wynikajacych z ww. ustawy, moze spowodowac uniewaznienie stopnia nabytego na podstawie tej rozprawy.
Kraków, dnia .................................... .................................. podpis doktoranta
Doctor of Philosophy
Development and evaluation of a signal analysis and a readout system of straw tube detectors for the PANDA spectrometer
by Pawe STRZEMPEK
In this thesis the prototype system for processing of the signals generated in the straw tube trackers of the PANDA spectrometer is proposed, built and evaluated. The full processing chain of signal consists of programmable readout electronics, config- ware and analysis methods. The proposed readout is based on the front end electronics, equipped with the configurable PASTTRECv1 ASIC (PANDA STT REadout Chip version 1 Application Specific Integrated Circuit) and the readout board (TRBv3 - Trig- ger Readout Board version 3) acting as data concentrator and time measurement device. The readout system performs full chain of data processing consisting of analog shaping, digital conversion and data transmission. A dedicated analysis methods have been developed to extract track position and a particle energy deposit in the detectors. Dedicated tests of the system by means of the cosmic rays and proton beams have been performed. The results prove that the spatial resolution better than 150 µm can be achieved. Furthermore, particle identification based on time over threshold method can be successfully applied in the momentum region below 800 MeV/c. The last but not least goal was to show that it is possible to realize complete readout system based on the concept presented in this thesis which is capable of cope with the hit rates of the PANDA spectrometer.
v
Rozprawa doktorska
Rozwój i ewaluacja systemu odczytu i analizy sygnaów z detektorów somkowych spektrometru PANDA
Pawe Strzempek
W niniejszej pracy zosta opisany, zbudowany i przetestowany prototyp systemu prze- twarzajacego sygnay generowanych przez somkowe detektory sladu spektrometru PANDA. We wspomnianym systemie, sciezka przetwarzania sygnau skada sie z pro- gramowalnej elektroniki odczytu, oprogramowania wbudowanego oraz metod analizy danych. Zaproponowana elektronika odczytu dzieli sie na elektronike przednia, wyposazona w konfigurowalny ukad ASIC (Application Specific Integrated Circuit) o nazwie PASTTRECv1 (PANDA STT REadout Chip version 1) oraz na pyte odczytu (TRBv3 - Trigger Readout Board version 3), której zadaniem jest koncentracja danych oraz pomiar czasu. System odczytu przeprowadza kompleksowe przetwarzanie syg- naów poczawszy od ksztatowania sygnau analogowego, jego konwersje do postaci cyfrowej a nastepnie cyfrowej transmisji. Rozwiniete zostay metody analizy danych suzace do okreslania sladów przelotów czastek przez detektor oraz pozwalajace okreslic ilosc zdeponowanej przez nie energii. Ponadto przeprowadzone zostay dedykowane testy systemu z promieniowaniem kosmicznym oraz z wiazka protonowa. W wyniku tych testów okreslono pozycyjna zdolnosc rozdzielcza detektora która spenia warunki (x ≤ 150µm ) stawiane przez eksperyment PANDA. Co wiecej rozpoznawanie czastek w oparciu o metode czasu nad progiem moze z powodzeniem byc zastosowane w obszarze pedów czastek ponizej 800 MeV/c. Ostatnim z wyznaczonych celów pracy byo wykazanie, ze mozliwa jest realizacja penego systemu odczytu detektora, przy wykorzystaniu koncepcji przedstawionych w niniejszej pracy, speniajacego stawiane wymagania w eksperymencie PANDA.
vii
Acknowledgements I would like to thank my dissertation advisor prof. Piotr Salabura for his time, help
and a lot of valuable advice. I would also like to thank my dissertation co-advisor dr Grzegorz Korcyl who not only taught me a lot but also was a great companion. Many thanks to my family and especially my wife Agata who has always been there to support and encourage me to finish this work.
Moreover, the presented work was supported by NCN based on decision number: [DEC-2013/09/N/ST2/02180].
ix
Contents
1 Introduction 1
2 PANDA experiment 5 2.1 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2.2 Physical motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2.1 The Quantum Chromo Dynamics . . . . . . . . . . . . . . . . . . 5 Charmonium spectroscopy . . . . . . . . . . . . . . . . . . . . . . 6
2.2.2 Gluonic excitation . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Hyperon physics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.3 Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.4 Spectrometer overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.4.1 Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.4.2 Magnets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.4.3 Subdetectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Micro Vertex Detector . . . . . . . . . . . . . . . . . . . . . . . . . 12 Electromagnetic calorimeter . . . . . . . . . . . . . . . . . . . . . . 13 Gas Electron Multiplier (GEM) . . . . . . . . . . . . . . . . . . . . 13 Detector of Internally Reflected Cherenkov light (DIRC) . . . . . 13 Ring Imagine Cherenkov light . . . . . . . . . . . . . . . . . . . . 14 Muon detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Central Straw Tube Tracker (STT) . . . . . . . . . . . . . . . . . . . 14 Forward Tracker (FT) . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.4.4 Straw tube trackers . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Principles of operation and construction of PANDA straws . . . 16 Purpose of the tracking system . . . . . . . . . . . . . . . . . . . . 19 Data rates in the straw tube trackers . . . . . . . . . . . . . . . . . 20
3 Architecture of the Readout System for the straw tube trackers 23 3.1 Data acquisition systems in nuclear and particle physics . . . . . . . . . 23
3.1.1 Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 3.1.2 Front end electronics . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3.1.3 Amplifiers, shapers and digitizers . . . . . . . . . . . . . . . . . . 26
ADC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 TDC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.1.4 Trigger system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.1.5 Data concentrators and storage . . . . . . . . . . . . . . . . . . . . 29 3.1.6 Event building and networking . . . . . . . . . . . . . . . . . . . . 30 3.1.7 Data processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.2 PANDA DAQ system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 3.2.1 DAQ overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
xi
3.2.2 The event building . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 3.2.3 The computing farm . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.3 Concepts of signal processing for the STT and FT . . . . . . . . . . . . . . 36 3.3.1 ADC based approach . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.3.2 Time over threshold approach . . . . . . . . . . . . . . . . . . . . 38
4 STT and FT signal processing 39 4.1 Front end electronics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
4.1.1 PASTTREC chip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Analog part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Digital part . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Difference between PASTTRECs versions . . . . . . . . . . . . . . 41
4.1.2 Front end board for PASTTRECv1 . . . . . . . . . . . . . . . . . . 41 4.2 TRBv3 as a readout platform . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.2.1 Time to digital converter . . . . . . . . . . . . . . . . . . . . . . . . 43 Zero suppression . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Time measurement resolution . . . . . . . . . . . . . . . . . . . . . 46
4.2.2 Data transmission and networking . . . . . . . . . . . . . . . . . . 46 Estimations of the maximal data bandwidth and limits of the sys-
tem performance . . . . . . . . . . . . . . . . . . . . . . 48 Efficiency and performance tests . . . . . . . . . . . . . . . . . . . 49
4.2.3 Integration of the slow control for the PASTTRECv1 . . . . . . . . 50 4.3 Event building . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.4 Analysis software for the FT prototype . . . . . . . . . . . . . . . . . . . . 52
4.4.1 Offline software design . . . . . . . . . . . . . . . . . . . . . . . . 52 4.4.2 Offline methods and procedures of the analysis . . . . . . . . . . 53
Time to radius calibration . . . . . . . . . . . . . . . . . . . . . . . 55 Track reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . 56 Track to wire distance and truncated mean . . . . . . . . . . . . . 57
4.4.3 Online quality assessment . . . . . . . . . . . . . . . . . . . . . . . 57
5 Measurements and tests 61 5.1 Laboratory equipment and setup . . . . . . . . . . . . . . . . . . . . . . . 61 5.2 Investigation of the PASTTREC configurations . . . . . . . . . . . . . . . 61
5.2.1 Optimal chip settings . . . . . . . . . . . . . . . . . . . . . . . . . 63 5.2.2 Gain and baseline uniformity . . . . . . . . . . . . . . . . . . . . . 64 5.2.3 Hit rate capability . . . . . . . . . . . . . . . . . . . . . . . . . . . 68 5.2.4 Tests with 55Fe source . . . . . . . . . . . . . . . . . . . . . . . . . 69
55Fe source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Dynamic range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Charge and TOT correlation . . . . . . . . . . . . . . . . . . . . . . 71 Threshold position investigation . . . . . . . . . . . . . . . . . . . 71
5.2.5 Evaluation of the prototype with the cosmic rays . . . . . . . . . 72 Baseline optimization . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.2.6 Cosmic rays data analysis . . . . . . . . . . . . . . . . . . . . . . . 73 Data sets and event filtration . . . . . . . . . . . . . . . . . . . . . 74 Track reconstruction . . . . . . . . . . . . . . . . . . . . . . . . . . 75 Detector efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 TOT separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
xii
6 In beam operation 79 6.1 Setup description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.2 Measurement conditions and data sets . . . . . . . . . . . . . . . . . . . . 80 6.3 Data analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.3.1 QA plots and calibration . . . . . . . . . . . . . . . . . . . . . . . . 80 6.3.2 Spatial resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 6.3.3 Particle identification . . . . . . . . . . . . . . . . . . . . . . . . . . 83
FT data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 STT data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
7 Summary and conclusions 89 7.1 Discussion of the results . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 7.2 Readout schematic for the STT and the FT . . . . . . . . . . . . . . . . . . 90 7.3 Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
A The use of FPGA based development boards for testing electronics 95 A.1 FPGA units and development boards . . . . . . . . . . . . . . . . . . . . 95 A.2 Signal routing and conversion . . . . . . . . . . . . . . . . . . . . . . . . . 96
B Slow control for the PASTTRECv0 99 B.1 Slow control protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
C Slow control for the PASTTRECv1 101 C.0.1 User interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 C.0.2 Configuration module . . . . . . . . . . . . . . . . . . . . . . . . . 101
D Energy loss of charged particles 105 D.1 Bethe formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 D.2 Most probable energy loss . . . . . . . . . . . . . . . . . . . . . . . . . . . 105
Bibliography 109
List of Figures
2.1 Formation of charmonium in e+e− (a) and in two different scenarios of pp annihilation (b,c). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2 The charmonium spectrum. Black lines denote charmonium states, and red dots indicate charmonium-like states. Blue lines indicate the thresholds at which states can decay into a pair of D mesons. Adapted from [5]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3 Illustration of the FAIR complex. The red color marks the part of the facility which is not yet constructed. Source: [1]. . . . . . . . . . . . . . . 9
2.4 Schematic view of the HESR. The place of the beam injection, experimental installations and devices for the beam cooling are marked. Source: [7]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.5 The PANDA spectrometer. . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.6 Left: Photography of one STT module. Right: View of the STT from the
beam direction. The red color indicates straw tubes skewed by −2.9o
whereas the blue by 2.9o. . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 2.7 The model of the FT1 and FT2 station. The hole inside the module is
planned for the beam pipe. . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.8 The straw tube construction on the example of STT tracker. . . . . . . . . 17 2.9 Simulated drift time in respect to the distance from the anode wire with-
out (left) and with (right) magnetic field presence. Adapted form [14] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.10 Simulated drift path of the electrons originating form the ionization process. The case without (left) and with (right) magnetic field is presented. Adapted form [14]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.11 Separation power in the STT detector for the energy bands built with particles all tracked with the same muon mass hypothesis. Source: [11]. 20
2.12 Simulation of pp reactions at 15GeV/c giving the number of hits per event and per cm along the tubes in the inner most layer of the STT PANDA [11]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.13 Number of counts per second expected in the individual straws placed in the X location. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.1 Schematic representation of the front end electronics functions with two concepts of signal shaping: A - with analog circuitry, B - inside the signal processor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2 The three levels of the ATLAS trigger and their event rates and processing time. Source: [21] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
3.3 Schematic of the DAQ general concept. The data streams from FEE to the DAQ endpoints, Concentrators and finally gets to the event builders via network. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4 A schematic view of the HADES network. The number refers to the number of boards in the system. Adapted from: [26]. . . . . . . . . . . . 31
xv
3.5 The general view of the PANDA DAQ architecture. The FEE is connected to the Data Concentrators which receive packets from SODANet network. The event building and event filtering is done in the Compute Node matrix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.6 Left: The schematic view of the CN architecture. Its basic building blocks are XILINX Virtex 5 FPGAs. The four central Virtexes are used as processing units and the fifth one is used to provide connection to FP- GAs from other CN via the ATCA backplane. Right: The photography of the µTCA compliant daughter board of CN. Source [29] and [27]. . . 34
3.7 The SODANet topology. Three types of protocols are marked. The red one represents the SODANet connection which main task is to distribute the clock and time information. The blue one is the Ethernet standard used for data transfer from DCs to EB. The black one is a custom protocol individually selected for each subsystem. Adapted from [31] . . . . . . . 35
3.8 Left: The representation of the real to conformal space transition performed by the Hough transform . Right: The example of the the conformal space for the line Hough transform. The local maximum corresponds to the line (particle trajectory) in the real space. Source [34]. . . . 36
3.9 The algorithm representation of clusters finding in the EMC detector. On the left the list of hits registered in one event. On the right upper the two dimensional space on which the hits are mapped. Arrows indicate the direction of the neighboring hits search. On the right bottom the order of the neighboring hits search. Source [33]. . . . . . . . . . . . . . . . . . 37
4.1 The micrograph of produced prototype of the PASTTREC. . . . . . . . . 40 4.2 Schematic of the internal PASTTREC architecture. The following com-
ponents are presented: preamplifier with first stage shaper (CR-RC), two stage tail cancellation circuit, baseline holder circuit and discriminator. . 40
4.3 Photography of the FEB and the high voltage decoupling board. The straw tubes are connected to the pads located on the right side (respect to the photography) of the decoupling board. . . . . . . . . . . . . . . . . 42
4.4 Left: the TRBv3 photography. Right: schematic representation of the TRBv3 components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.5 Schematic representation of time acquisition by TDC. Each TDC channel stores information in ring buffer which is filled by header (1 word), epoch counter (1 word) and consecutive hits (2 words per hit). . . . . . 44
4.6 The fine time calibration step function which translates the TDC bin information (x-axis) into time information (y-axis) . . . . . . . . . . . . . . 45
4.7 The stretcher offsets values for each of the channel in one TDC. . . . . . 46 4.8 The RMS values of the lead time difference between two consecutive
channels of the FEE and TDC. . . . . . . . . . . . . . . . . . . . . . . . . . 47 4.9 Schematic representation of tree like architecture of the TRBv3 system.
The black line connecting the HUBs indicates TRBnet protocol. Each endpoint can have FEBs connected but for the simplicity only several FEBs were drawn. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
4.10 A simplified schematic of TRBv3 architecture. . . . . . . . . . . . . . . . . 48 4.11 Overall (payload and headers) data transfer rate from TRBv3 depending
on the read request frequency. The hit rate per channel was set to 1 MHz. 49
xvi
4.12 The correlation between the multiplicity of hits and the hit rate. Above 250kHz the constant hit multiplicity of∼ 50 is present which corresponds to the saturation of the ring buffer. Slight increase of the number of recorded hits appears due to the decreasing number of epoch counter words with the increasing data rates. The data was taken for a single channel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
4.13 Multiplicity of registered hits coming from one generation series produced by Virtex5. One generation series consists of 100001 simulated hits. The read request in TRBv3 was generated with internal generator set to 5kHz. The histogram shows number of hits collected by a single channel. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.14 Schematic representation of the class designed, implemented and used in analysis software. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
4.15 The GUI of the event display designed for the FT prototype. On the canvas the prototype detector geometry is displayed together with one event. The black and the red straight lines represents reconstructed trajectories of the particle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.16 Schematic representation of the data analysis stages. On the left side the input files for the macros which runs the analysis. On the right the data structure of the output files. The meaning of the names is as following: globEvNum - global event number, chNum - channel number, ftTDC2 - drift time, TOT - time over threshold, driftR - drift radius, X - x coordinate of the straw that fired, Z - z coordinate of the straw that fired, a, b, a_err, b_err - the parameters of the prefit, a_mi, b_mi - the parameters of the Minuit fit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.17 The hit multiplicity per event for cosmic rays data which was taken with the setup described in section 5.1. The hits number maximizes at 6 what corresponds to the number of the straw tube layers used in the measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.18 Exemplar calibration curve done for the data collected with the cosmic rays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.19 Generation of the signal inside the straw. Particle crossing the straw close to the anode wire (left) leaves more charge than the one crossing close to the wall (right). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
4.20 TOT simulation with single straw response (top) and truncated aver- aged on 24 straws (bottom) for proton and charged pion and kaon with 0.5 GeV/c momentum. Solid red lines show the Gaussian fit to the distributions. The protons, charged kaons and pions are well distinguished using distance corrected TOT after applying the truncated mean by dis- carding the 30% of the largest values. [14] . . . . . . . . . . . . . . . . . . 59
4.21 The graphical user interface of the go4. . . . . . . . . . . . . . . . . . . . 59
5.1 A: Prototype detector setup installed at Jagiellonian University in Krakow. The setup consist of 3 vertically oriented FT modules (96 channels in total). B: Schematic view of the detector arrangement with rough dimensions marked. C: Block diagram showing connection of the detector, FEBs and the TRBv3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.2 Set of analog pulse shapes taken with the delta pulse for all combinations of the preamplifier gain settings (0.67, 1, 2, 4 mV/fC) and the peaking time settings (10, 15, 20, 35 ns). . . . . . . . . . . . . . . . . . . . . . . . . 64
xvii
5.3 Left: Amplitudes of 16 output signals versus input charge for the same ASIC configuration (see text for details). Right: Distribution of the baseline levels accumulated from 198 channels. . . . . . . . . . . . . . . . . . 68
5.4 Gain measurements for delta pulses for four settings of preamplifier gain parameter (K). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
5.5 The analog output of the PASTTREC chip responding to the pulse cou- pled to the FEB input test. The input pulse frequency equals 2 MHz.
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 5.6 The TOT spectrum of 55Fe taken with high voltage set to 1700 V. The
strong right peak corresponds to the full absorption of the 5.9 keV X- rays, and it is clearly separated from the 2.9 keV argon escape peak on the left. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
5.7 TOT and charge correlation. The charge was obtained by taking into account the number of primary electron production amplified according to gas gain function. The TOT values come from Gaussian distribution fitted to TOT spectrum which was collected with 55Fe source. . . . . . . 72
5.8 Correlation between separation parameter and threshold position. Sep- aration parameter calculated according to the equation 5.1. The data taken with the iron radioactive source at straws high voltage set to 1700V. 73
5.9 Left: TOT spectrum versus channel number for selected channels of the detector before the baseline tune procedure was applied. The white bars corresponds to disconnected straw tubes. Right: TOT spectrum versus channel number for selected channels of the detector after the baseline tune procedure was applied. The channels above 32 have less statistic as they belong to the second module of the straw tubes which was located 10 cm farther from the iron source (see section 5.1). . . . . . . . . . . . . . 74
5.10 Left: Drift time spectrum versus channel number for all the 96 channels of the system. The white bars correspond to disconnected straw tubes. Right: Projection of the drift time spectrum for all the 96 channels. . . . 75
5.11 Left: TOT versus drift time correlation for 1800V and threshold 21 mV. Data for all the hits in the detector. Right: TOT versus drift time correlation for 1800V and threshold 21 mV for the reconstructed tracks. Divid- ing number of entries by 6 (average hit multiplicity) results in estimation of number of reconstructed tracks (∼6500) in the data set. . . . . . . . . . 76
5.12 The histograms of residuals for different cosmic ray data sets. . . . . . . 76 5.13 The FT prototype straw tubes placement. Example event is drawn which
contributes to the detector inefficiency. . . . . . . . . . . . . . . . . . . . . 77 5.14 Left: Efficiency versus hit position for two different threshold levels and
the same voltage (1800 V) at the detector. Right: Efficiency versus hit position between two different high voltages at the detector (1700 and 1900V) and the same threshold 21 mV. . . . . . . . . . . . . . . . . . . . . 78
5.15 Comparison of the TOT mean spectra for cosmic rays for different high voltages applied to the detector and two thresholds: 5mV (left), 21mV (right). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
6.1 The schematic representation of the detector modules placement during the proton beam tests. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
6.2 Left-upper: The drift time spectra for all 96 channels of FT system. Right- upper: TOT spectrum for all 96 channels of FT system. Lower: Drift time spectrum for one selected straw tube. . . . . . . . . . . . . . . . . . . . . 81
xviii
6.3 Left: Drift time versus TOT correlation for all hits. Middle: Drift time versus TOT correlation for the hits belonging to the successfully reconstructed tracks. Right: Drift time versus TOT correlation after perform- ing the TOT geometrical calibration. . . . . . . . . . . . . . . . . . . . . . 82
6.4 Residual distribution as a function of the drift time of the reconstructed proton tracks (proton momenta 750 MeV/c) . . . . . . . . . . . . . . . . . 82
6.5 Left: Residual distribution for different PASTTRECv1 settings (see text for details) and different beam momenta. Right: Residual distribution for different thresholds, default PASTTRECv1 setting and different beam momenta. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
6.6 Energy loss measurement for different particles at different momenta. Plot was done from data taken with time-projection chambers by the PEP4 experiment. Adapted from [12]. . . . . . . . . . . . . . . . . . . . . 84
6.7 TOT truncated mean 20% for different proton momenta. Data taken with the FT detector, threshold equal 10 mV and setting2. . . . . . . . . . . . 84
6.8 Dependence of TOT measurement on thresholds. Left: TOT truncated mean for four beam momenta. Middle: TOT truncated mean resolution for the four beam momenta. Right: Separation power calculated for each beam momenta with respect to the minimum ionizing protons. . . . . . 85
6.9 Dependence of TOT measurement on settings of the PASTTRECv1. Left: TOT truncated mean for four beam momenta. Middle: TOT truncated mean resolution for the four beam momenta. Right: Separation power calculated in respect to MIPs (p=3GeV/s). . . . . . . . . . . . . . . . . . 85
6.10 Separation power as function of βγ for protons, pions and kaons. Result obtained with default settings of the PASTTRECv1 and threshold set to 10 mV. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
6.11 TOT truncated mean for the protons with 750 MeV/c momentum obtained for different event ranges saved in a single file. The significant differences in the spectrum shapes may indicate that the measuring conditions were not stable in time. . . . . . . . . . . . . . . . . . . . . . . . . 87
6.12 TOT truncated mean 40% for different proton momenta. Data taken with the STT detector, threshold equal 10 mV and setting2. . . . . . . . . . . . 87
6.13 Left: Cumulative distribution function and probability of identification proton with momentum 550 MeV/c and pion with momentum 550 MeV/c mimic by the minimum ionizing proton (3 GeV/c). Right: Cumulative distribution function and probability of identification proton with momentum 550 MeV/c and kaon with momentum 550 MeV/c mimic by the quasi minimum ionizing proton (1 GeV/c). . . . . . . . . . . . . . . 88
7.1 Schematic of the suggested readout of the STT detector. The readout is based on the TRBv3 boards and the FEB equipped with the PAST- TRECv1 chip. Compare with figure 3.7. . . . . . . . . . . . . . . . . . . . 91
A.1 Architecture of single logic block. . . . . . . . . . . . . . . . . . . . . . . . 95 A.2 Full development path of the configuration file for the FPGA. Code writ-
ten in VHDL is synthesized into logic which is later mapped to the available resources inside FPGA. In the zoom the single logic blocks are visible. 97
B.1 The graphical user interface for the prototype FEB. . . . . . . . . . . . . . 99 B.2 The command word format used to control the prototype front end board.100
xix
C.1 The snapshot of the currently used graphical user interface for the FEE setup. The GUI is integrated with the TRBv3 system. . . . . . . . . . . . 102
C.2 Waveform of the TRBv3 to PASTTRECv1 communication. The callback line is used for back transmission of saved value in the register. . . . . . 102
D.1 Mean energy loss rate in different materials. . . . . . . . . . . . . . . . . . 106 D.2 Function of energy loss (here denote as /x) in silicon material for 500
MeV pions, normalized to unity at most probable value. Adapted from [12] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
D.3 Energy loss in a straw tube (blue dashed histogram) compared with the sharper Landau distribution (black histogram). Simulation done for a 1 GeV/c pion crossing tube filled with a ArCO2 (90/10) gas mixture at 2 bars. Adapted from [52]. . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
xx
List of Tables
2.1 Size, placement and number of straws in each FT station. . . . . . . . . . 16 2.2 Properties of the argon and the carbon dioxide. Ex and Ei are the ex-
citation and ionization energies. Wi is the minimal energy necessary to produce one electron-ion pair in the gas. dE/dx is the most probable energy loss of the minimum ionizing particle in the gas. Np and Nt are the number of primary and total electrons per cm, respectively. X0 is the radiation length. Adapted from [12] . . . . . . . . . . . . . . . . . . . . . 18
4.1 Description of the PASTTRECv1 registers. . . . . . . . . . . . . . . . . . . 41 4.2 The data format of the time data word [42]. . . . . . . . . . . . . . . . . . 51 4.3 Steps of a data processing form binary file to user’s result file. . . . . . . 52
5.1 Three optimal settings found for preamplifier gain equal 1 mV/fC and peaking time equal 15 ns. . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
5.7 Complete set of data collected with the cosmic rays. . . . . . . . . . . . . 74
C.1 The command word structure send from the PC to the configuration module implemented inside FPGA. The lower nibble (19 LSB) is forwarded to the PASTTRECv1. X – not important bits, R – reset bit. If set to 1, both PASTTRECv1 chips placed on FEB, which address is indicated by the CC bits, are reset, C – cable connector number. 00 – connector 1, 01 – connector 2, 10- connector 3, 11 – connector 4 (which should not be used as one TDC can measure time form maximally 3 FEE), H – header, should be 1010. After ASIC decodes this bit sequence it starts to decode the rest of the command word, S – select ASIC. One FEE board has two ASIC chips, in order to distinguish them each has individual address 10 or 01, O – read or write operation. 1 – read, 0 – write. Once read operation has been selected the addressed register is only read (its value is transmitted over the SPI return line), whereas write operation alter the register and previous value of register is transmitted over SPI return line, A – 4 bit ASIC register address, V – 8 bit ASIC register value. . . . . . . 103
xxi
List of Abbreviations
ADC Analog to Digital Converter ASIC Application Specific Integrated Circuit CFD Constant Fraction Discrimination CN Copute Node CTS Central Trigger System DAQ Data AcQuisition DC Data Concentrator DIRC Detector of Internally Reflected Cherenkov light EMC Electro Magnetic Calorimeter FADC Flash Analog to Digital Converters FEB Front End Borad FEE Front End Electronics FPGA Field Programmable Gate Arrays FT Forward Tracker FS Forward Spectrometer GEM Gas Electron Multiplier HLM High Luminosity Mode HRM High Resolution Mode IP Interaction Point MDT Mini Drift Tubes MIP Minimum Ionizing Particles MVD Micro Vertex Detector PCB Printed Circuit Board PID Particle IDentification PT Peaking Time RICH Ring Imagine CHerenkov SODANet Synchronization Of Data Acquisition Network STT Straw Tube Tracker TC Tail Cancellation TDC Time to Digital Converter TOT Time Over Threshold TRB Trigger Readout Board TS Target Spectrometer VHDL Very high speed Hardware Description Language QA Quality Assessment
xxiii
Introduction
In 1896 Henri Becquerel discovered that samples of uranium ore leave marks on the photographic plates. His discovery gave a foundation for new scientific discipline - nuclear physics. Becquerel’s work inspired Marie Curie Sklodowska who followed his findings and together with her husband (Pierr) have discovered radium and polonium, two radioactive chemical elements extracted from uraninite ore sample.
A huge step forward in the investigation of radioactivity was done by Ernest Ruther- ford who is called the father of nuclear physics. He discovered the half-life period prin- ciple but the most famous experiment that he performed was irradiation of golden foil with alpha particles which proved that the atoms consist of orbital electrons moving around protons concentrated in the center of the atom forming nucleus.
Another mile stone was reached at the beginning of 1932, when James Chadwick discovered the neutron which as a neutral particle could more easily than proton reach the nucleus of atom. This effect was used by Enrico Fermi who has proven that neutron bombardment can lead to artificially induced radioactivity. No more than five years passed and neutron induced uranium fission was performed which led to construction of nuclear reactors and uranium-fission bombs.
Till 1960s people believed that protons and neutrons were the smallest possible particles. The situation has changed after the investigation of deep inelastic scattering at Stanford Linear Accelerator Center which confirmed existence of quarks proposed by the quark model introduced in the 1964. This discovery led to general acceptance of the Standard Model (SM) which had been evolving since several years at that time.
The SM is a theory unifying description of the electromagnetic, weak and strong interactions among the particles. Even though the theory is not full (does not include the gravitation interaction) it has many successful experimental confirmations like for example discoveries of the W and Z bozons existence or charm and bottom quarks. In order to be able to compare further SM predictions with the underlying physical properties of the nature the physicists need to construct more advanced and sophisticated detecting machines which are able to record particles created in the collisions of high energy particle beams with stationary target or another counter beam.
An example of such a sophisticated detector is the one being built for the PANDA (anti-Proton ANnihilation at DArmstadt) experiment which will work at the high energy storage ring accelerator at FAIR facility in Darmstad. The detector will operate with a fixed proton target where proton-antiproton collisions will take place at the beam momentum in range 1.5 - 15 GeV/c. The research program aims to study the physics of the strong interactions described by the Quantum Chromo Dynamics.
The spectrometer, designed for the PANDA experiment, will measure different reaction products by means of many sub-detectors. One of them is a tracking system which is responsible for reconstruction of the particle tracks inside a dedicated magnetic field. Second task of the tracking system is the energy loss measurement which is
1
intended for the particle identification. This thesis work focuses on investigation and development of a dedicated readout
system for the PANDA tracking detectors. The main these of the work is defined as following: "A dedicated readout system for the signals generated by straw tubes designed for the PANDA experiment can be built with the signal amplifying, shaping and discriminating front end electronics based on the PASTTRECv11 chip connected to the Triggered Readout Board (TRBv3). Such a readout schematic fulfills the PANDA spectrometer requirements for 150 µm spatial resolution and enables particle identification based on energy loss measurement with Time-Over-Threshold method". The main goals of the work which are required to prove the quoted these can be characterized as:
• Prove that the readout system together with the straw tubes detector is capable of recording trajectories of particles with spatial resolution no worse than 150 µm.
• Prove that the concept of the Time-Over-Threshold method for energy loss measurement is sufficient for particle identification in the beam momentum range below 800 MeV/c.
• Present a proposition of readout architecture for the whole tracking system.
In order to fulfill the above goals the following additional tasks need to be targeted:
• Preparation and tests of individual hardware components of the system.
• Preparation of the data acquisition, control software and firmware for the system.
• Construction of the prototype readout and its performance tests. Measurements with the prototype and proton beams of various momenta.
• Development and commissioning of the analysis methods needed for verification of the requirements.
The research on the specified goals has been completed and the results are presented in the chapters which are structured as following.
Chapter 2 gives the physical motivation and research overview of the PANDA experiment. The characteristic of the spectrometer is described with special attention to the construction and purpose of the tracking system based on straw tubes detectors.
Chapter 3 is dedicated to general description of data acquisition systems in nuclear and particle physics and its comparison with the concept proposed for the PANDA. This section ends with discussion of two general approaches of digitization the PANDA straws chosen by the collaboration.
Chapter 4 presents all components of the full chain signal processing consisting of: PASTTREC which amplifies, shapes and discriminates analog signals, the TRBv3 readout board which measures the time of the arrival and the time over threshold and transmits the data to the PC for storage and a dedicated analysis software.
Chapter 5 contains description of tests performed with the front end electronics as well as with the readout board. Tests of whole prototype system combined with the detector are shown in the final sections.
Chapter 6 focuses on the results obtained with the detector and proton beams with a different momenta.
The discussion of the results from laboratory tests and in the beam measurements are summarized in chapter 7 which presents also a proposition of the readout system
1PANDA Straw Tube Tracker REconfigurable Chip
Chapter 1. Introduction 3
of the PANDA tracking system. Whole work is closed with the summary and future plans.
Chapter 2
PANDA experiment
2.1 Overview
The PANDA (AntiProton ANnihilation at DArmstadt) is one of the most important experiment planned to operate in the Facility for Antiproton and Ion Research (FAIR) at GSI, Darmstadt [1]. The core of the FAIR will be a new synchrotron SIS100 providing primary proton (with maximum energy of 29 GeV) or heavy ion (with maximum energy 1.5 GeV/u for U28+) beam. Anti-protons beams, of very high intensity and quality, will be provided as secondary beams and stored in the dedicated High Energy Storage Ring (HESR) (see section 2.3 for more details). They will interact with stationary target. The expected available center-of-mass energy will be in range 2.3-5.5 GeV which will enable the spectroscopy of charm above the open charm threshold (3.74 GeV) as well as double and triple hyperons.
The following sections of the chapter are dedicated to more detail description of some selected aspects of the physics program of the PANDA, the accelerator complex and the spectrometer which is under construction and it will be used to fulfill the research program.
2.2 Physical motivation
The PANDA experiment posses very rich scientific research program which is shortly presented in this section. More complete information can be found in [2].
2.2.1 The Quantum Chromo Dynamics
The Quantum Chromo Dynamics (QCD) is a very successful theory which describes the strong interaction occurring between the quarks. The interactions force between the QCD objects can be explained with the boson exchange (gluon), similar to the Quantum Electromagnetic Dynamics theory (QED), where the same mechanism exists and the exchanged boson is the photon. The quarks as well as gluons carry strong charge which is called the color. In terms of the QCD the nature is colorless, it means that no free quarks or gluons can be observed. Instead these particles are confined in the states of total color charge equal zero. The confinement, which is the consequence of the gluon self interaction, is characterized by a coefficient called the coupling constant (αs) which depends on the distance between the QCD objects.
At low energies (short distances) the coupling constant is large thus quarks and gluons are closed in the hadrons. In this region the QCD may be approximated with the Chiral Perturbation Theory, whereas in the high energy region, where αs is small and quarks can be considered as free particles, the perturbative theory is applicable.
5
6 Chapter 2. PANDA experiment
The perturbative methods fail to describe the medium energy domain, where more experimental data (hopefully delivered by PANDA) is needed to evaluate proper theory.
Charmonium spectroscopy
The charmonium spectroscopy begun in 1974 with the discovery of the J/ψ resonance by the two experimental groups at Brookhaven and SLAC [3],[4]. Soon after this discovery the latter group found also the ψ′ resonance. New particles were identified as being bound states of not observed before charmed quark and its antiquark (cc) which mass mc = 1.27GeV/c2 is much bigger than the mass of u,d and s quarks. A bound state with the hidden charm are called quarkonia and in case of cc we speak of charmonium.
In the particle physics mesons which contain one c quark (or anti-c quark) are called D mesons and are considered as having an open charm. It has been shown that charmonium spectroscopy is a very convenient tool for studying the QCD bound system. Thanks to the big mass of the c quark it is possible to use the non-relativistic quark potential models which predict the bound states and narrow resonances.
Both SLAC and Brookhaven groups were using the e+e− annihilation in their experiments. In such a system direct creation of charmed mesons is possible only for the JPC = 1−− states. Such a limitation is not present in the antiproton-proton collisions where proton quarks annihilate with the anti-proton quarks and thus make it possible to directly form states with all possible quantum numbers. It is demonstrated with the Feymann diagrams presented in figure 2.1. This is the reason why the PANDA experiment plans to use the anti-proton beam.
e+
e-
γ
c
a) b) c)
FIGURE 2.1: Formation of charmonium in e+e− (a) and in two different scenarios of pp annihilation (b,c).
In figure 2.2 the charmonium spectrum is shown. It can be divided into two regions: the one below and the one above the open charm threshold (3.73 GeV). The part of the spectrum below 3.73 GeV is almost completely theoretically understood and is well explored with the experiments. Above the threshold there is a lot of new states called XYZ which were discovered at B-factories (decays of B mesons which consist of at least one b quark). Here the situation needs further exploration.
Operating at the D meson production threshold (corresponding to the beam momentum of 6.4 GeV/c) PANDA will measure the well-known D and Ds mesons. A large quantity of D mesons can be produced with favorable background conditions, as the phase space for additional hadrons is small. Thanks to the narrow beam momentum spread it will be possible to measure masses with accuracies of the order of 100 keV and widths to 10% or better by means of the fine scan.
PANDA operating with the high luminosity, excellent beam momentum resolution, detector with great spatial coverage and precise magnetic field will be able to deeply
Chapter 2. PANDA experiment 7
FIGURE 2.2: The charmonium spectrum. Black lines denote charmonium states, and red dots indicate charmonium-like states. Blue lines indicate the thresholds at which states can decay into a pair of D mesons.
Adapted from [5].
explore the charmonium mass region for the well established states and the newly discovered XYZ states which are expected to be classified concerning their quantum number configuration.
2.2.2 Gluonic excitation
Beside a relatively simple mesonics states (qq) the QCD allows also existence of the objects with excited glue. Such states consist of the quark, antiquark and additionally gluon resulting in qqg resonance called hybrid. The excited gluonic component contributes to the bound state quantum numbers (JPC) what increases the degree of freedom in comparison to the qq states. Thanks to the exotic quantum numbers of hybrids, which cannot be accessed by mesonic states, the mixing of qqg and qq is not possible and therefore hybrids are predicted to be rather narrow and easy to identify experimentally.
Furthermore, the QCD foresees the existence of colorless gluonic hadrons consisting only from gluons (ggg), which are called the glueballs. The glueballs fall in two categories: the ones without exotic quantum numbers and the ones with exotic quantum numbers (oddballs). It is possible that due to different spin structure of oddballs in comparison to glueballs, the difference of the properties of the two will reveal insight into the unknown glueball structure.
The hybrids and gluons are interesting objects as they are described by the low energy features of the QCD and their investigation will put light to the studies of the QCD vacuum structure.
Hyperon physics
The hypernuclei is created when the proton or neutron of the nuclei is replaced by one or more hyperons. So far only single (with one Λ hyperon) and double (with two Λ hyperons) hypernuclei were discovered. The use of antiproton beam (as planned at PANDA) will lead to efficient production of hypernuclei of higher order which will enable the studies of nucleon-hyperon interactions as well as extend the nuclear structure spectroscopy studies. Not to mention the importance of this research for other disciplines like astrophysics, where hyperon-nucleon interaction is essential for the un- derstanding of the neutron stars equation of state.
In the PANDA experiment a double target is foreseen for the hypernuclear studies. The signature of the reaction is the antiproton which interacts with the light target producing a pair of e.g. Ξ−Ξ
+. The double strange Xi particle is rescattered and it is captured in the secondary target where it forms Ξ−hypernuclei which eventually is transformed into a double Λ-hypernuclei. Such a nucleus is not stable and the Λ de-excitation in nuclear potential can be registered via γ−rays production.
Also systematic spectroscopy of Hyperons containing two and three strange quarks is foreseen. Presently only a few ground states of such baryons are known while quarks models predict many excited states which needs to be discovered.
2.3 Infrastructure
Operation of the PANDA experiment could not be possible without the advanced accelerator facility capable of ions and antiprotons production. This demand is met by the forehead mentioned FAIR complex which will be built at the site of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. There are four research pillars at FAIR, these are:
• Physics with High Energy Antiprotons - represented by the PANDA,
• Atomic, Plasma Physics and Applications (APPA) which focus on investigations of properties of QED in a presence of strong electric and magnetic fields and nuclear matter under extreme conditions (i.e. high field, high pressure, high temperature)
• Nuclear Structure, Astrophysics and Reactions (NUSTAR) which will use the radioactive beams for investigation of nuclear structure and dynamics. NUSTAR includes also nuclear astrophysics investigations.
• Nuclear Matter Physics - represented by Compressed Baryonic Matter (CBM) experiments which goal is to explore the QCD phase diagram in the region of high baryon densities.
The whole complex is shown in the Fig. 2.3. The red color marks the parts of the facility which are still to be built. The beam formation will start in the p-LINAC which will produce the protons or ions which will be later accelerated by the SIS18 synchrotron to the 4.7 GeV (protons) or 1 - 2 A GeV (ions). Then the beam will enter
FIGURE 2.3: Illustration of the FAIR complex. The red color marks the part of the facility which is not yet constructed. Source: [1].
SIS100 for further acceleration. In case of the protons the energy obtained at this stage equals 29 GeV and the number of particles per cycle reaches 2 x 1013 [6]. The next stage is the conversion of the protons to antiprotons which will be done on the target shield possibly made of light metal (i.e. copper, iridium) in order to avoid shield melting upon high energy proton irradiation on the one hand but heavy enough to produce sufficient amount of antiprotons on the other hand. The production rate of 5 x 10−6 antiproton per proton is foreseen. The extracted antiprotons are gathered by the Collector Ring, which performs stochastical pre-cooling and later are forwarded to the High Energy Storage Ring (HESR).
The total circumference of the HESR will be 574 m and it will have two curved parts and two linear parts (132 m). One of them will be occupied by the stochastic cooling system and electron cooling system. The other linear part will be partly occupied by the experimental hall dedicated for the PANDA. The hall will have 43m x 29m floor space and 14.5m height. The HESR will be able to ac-/decelerated antiprotons to the desired momentum.
The HESR will be able to operate in two modes: low luminosity mode with high momentum precision p/p = 4 × 10−5 (at luminosity 2 x 1031cm−2s−1) or high luminosity (2 x 1032cm−2s−1) with comparably higher momentum spread.
2.4 Spectrometer overview
The PANDA detector was designed to achieve 4π geometrical acceptance, very good resolution for track reconstruction, high efficiency of particle identification and being able to cope with very high interaction rates (up to 2× 107/s). The design includes also the versatile readout system with online event selection.
There are several characteristics of the measured particles which have to be established by the spectrometer. These are: event topology, particle species and full dynamics. The complete detector design is divided into many subdetectors responsible for determination of one (or more) of the mentioned characteristics.
FIGURE 2.4: Schematic view of the HESR. The place of the beam injection, experimental installations and devices for the beam cooling are
marked. Source: [7].
Knowing the event topology means that the vertex (place of particle origin/creation) is well defined. The event topology is known based on the tracking procedure which allows to reconstruct whole flight trajectory of the particle. Mainly the following subdetectors are used for the tracking (see figure 2.5): Micro Vertex Detector (MVD), Straw Tube Tracker (STT) and Gas Electron Multiplier (GEM). These three modules are called the Central Tracker covering central region around the target. There is also tracking system localized at the forward direction, Forward Tracker (FT), as a part of Forward Spectrometer , described in details below.
The second characteristic is particle species, which can be determined based on energy loss measurement (which depends on the particle velocity) or by simultane- ous velocity and momentum measurement. For the energy loss measurement mainly Muon system and Electromagnetic Calorimeter (EMC) will be used but also STT may bring important input here. For the velocity measurement the Ring Imagine Cherenkov (RICH) and the Detector of Internally Reflected Cherenkov (DIRC) is planned to be used in the range of high momentum whereas in the low momentum region the Time of Flight (TOF) system is proposed. The momentum will be extracted from the investigation of the particles’ trajectories bending in the magnetic field.
The last characteristic is the full dynamics which gives information about the total momentum and the energy of the particle. Therefore the dynamics of an particle is described by the four-momentum which is formed from the measured momentum (deduced from the tracking) and the detectors used for energy deposit measurement (EMC and Muon System).
In order to estimate the mentioned characteristics, the PANDA detector will be composed of two parts: the Target Spectrometer (TS) and the Forward Spectrometer (FS). The first one will cover the space around the interaction point (IP), which is the place where high energy beam meets the stationary target. The FS will register the particle going in the forward direction in the angles down to 5o in the vertical and 10o
in the horizontal plane.
The TS will consist of many subdetectors arranged in multiple layers surrounding the IP. The closets to the IP will be the MVD which main responsibility will be reconstruction of the primary vertex. After the MVD the STT module is planned to be placed. EMC will be the last component in the closets vicinity of the IP and it will be placed in the electromagnetic field created by the superconductive magnet coils which will be placed just after it but before Muon system. The TS is closed with the front end cap including GEM, Disk DIRC and EMC detectors.
The FS will be situated behind the TS looking from the beam direction. It will be responsible for registration of the particles emitted at low angles (±5o in the vertical and 10o in the horizontal plane). The FS will consist of RICH, EMC, Muon system, TOF and FT. Important element will be the dipole magnet causing the particles deflection needed for the momentum reconstruction.
The model of proposed spectrometer with all the subdetectors marked is presented in the Fig. 2.5. More detailed description of the most important subdetectors is placed later.
FIGURE 2.5: The PANDA spectrometer.
2.4.1 Targets
The particles registered by the spectrometer originating from interactions between the beam and the target. There are two main concerns regarding the target realization which are vital for successful experiment: the target thickness and its position. The position is crucial for the definition of the IP and the target thickness has direct impact on the number of interactions. There are two different types of the targets foreseen for the PANDA. The first one is the hydrogen gaseous targets used in proton-antiproton studies and the second one is the solid target in form of foil or thin wire used for studies of antiproton nucleon reactions. For the latter studies also gaseous target with heavier gases can be used.
When it comes to the gaseous targets, there are two main methods of their formation that are currently under evaluation. The first one is a cluster jet target which is realized by injecting the pressurized hydrogen into the vacuum via a special nozzle. The hydrogen forms a narrow jet clusters which are seen as high homogeneous density
targets. The drawback of cluster jets is high lateral spread leading to uncertainty of the IP definition.
The second method produces the target in the form of frozen hydrogen drops (pellets) falling freely and crossing the antiproton beam. The pellet target assure high effective densities but have no uniform time distribution (discrete pellets crossing the beam line). Therefore the beam must be extended to guarantee crossing with many pellets which forces finding the balance between average luminosity and the beam spread.
In both solutions it seems to be possible acquiring the target density in the order of 4 × 1015 hydrogen atoms per square centimeter which together with the number of antipronts (1011) hitting the target every 2 µs, results in the desired beam luminosity in the order of 2× 1032 cm−2s−1.
Due to the limitation on the material budged and space, the target production system, including vacuum pumps, will be installed on the top of the TS and the jets or pellets will be delivered to the IP via 100 mm in diameter tube going through the subdetectors of the TS as well as the solenoid magnet.
2.4.2 Magnets
The magnets play an important role in the PANDA spectrometer as they bend the charged particles trajectories which enables their momentum calculation. There are two magnets foreseen: a solenoid type and a dipole type. The solenoid magnet will have 2.8 m length and inner diameter equal 90 cm and will be installed in the TS. The field will amount to 2 T and its fluctuations will not exceed ±2%. The second magnet is of the dipole type and will be installed in the FS. It will occupy 1.6 m in the beam direction starting from 3.9 m downstream of the target. The magnet will cause the deflection of the beam. To minimize this effect there will be the possibility of dumping down the filed for the time of acceleration of the antiprotons and also two correcting dipole magnets are planned to be used around the spectrometer. More comprehensive description of the magnets can be found in [8].
2.4.3 Subdetectors
In this section all the subdetectors comprising the PANDA spectrometer are shortly described. The straw tube based modules (STT and FT) are described in more details at the end of the chapter. More complete description of a the subdetectors can be found in [2].
Micro Vertex Detector
The Micro Vertex Detector is the pixel detector similar to the one used in the ATLAS experiment. It bases on the silicon pixels in which upon particle crossing the electrons and holes pairs are created. As the pixel is polarized, the pairs are pulled in opposite directions until they reach the pads which connect the pixel with the readout electronics.
The detector is planned to be divided into 4 barrel layers surrounding the IP and six discs placed in the forward direction in respect to the beam. The first barrel will be placed 2.5 cm away from the IP and the most outer one will be situated at the distance of 12.5 cm. The last two barrels and the last two disc are made of silicon strips and the remaining part of the MVD is equipped with the pixels of 100 x 100 µm.
The main goal of designing the MVD detector is the reconstruction of the primary vertex and the secondary vertex with the resolution better than 100 µm which is required for identification of the short lived particles. Additionally, the MVD can con- tribute to the particle identification via some energy loss measurement and it can bring improvement of the momentum resolution.
Electromagnetic calorimeter
The electromagnetic calorimeter is a detector dedicated to energy measurement by the total particle absorption and additionally designating the place of the absorption. The decay channels containing the photons or leptons are of high importance therefore two types of calorimeters have been foreseen in the final spectrometer design.
The first one is located inside the magnetic field of solenoid what limits the radial thickness of the calorimeter. It has a barrel shape and two end-caps providing hermetic- ity. The total number of 15552 crystals are planned to be used, each 200 mm long. The crystals have to be able to produce fast responses to incident particles in high counting rate environment, deliver sufficient energy resolution and detection efficiency of the photons and leptons in a high range of energy. Also the radiation hardness has been taken into consideration while searching for optimal crystals material. The lead tungsten (PbWO4) crystals are chosen as a high density inorganic scintillator [9].
The second EMC is of a shashlik type, which means that the detection modules (plastic scintillators) are interleaved with the lead plates. It is situated in the FS after the dipole magnet and it consists of 1404 modules 55x55 mm2 cell size each.
Gas Electron Multiplier (GEM)
The main part of the GEM detector is a very thin polymer foil which is metal-coated on both sides. There are many micro dimensional holes in the foil (typically 50-100 mm2). The large difference of electrical potential, applied to the both sides of the foil, generates strong electric field inside the holes. Strong field causes each electron inside the hole to create an electromagnetic avalanche containing typically 100-1000 electrons. Multi- plied electrons are then led to the readout plates from which the front end electronics can capture the signal.
In the spectrometer, three planar plates of the GEM detectors are planned to be installed. All of them situated downstream of the target at 1.1 m, 1.4 m and 1.9 m position. The main purpose of GEM installation is detection of the particles escap- ing the STT detector in the forward direction (below 22o). The very high counting rates (3× 104cm−2s−1 close to the beam pipe) are not acceptable for the drift chambers, which would suffer from aging effect due to too high occupancy, therefore use of the GEMs in this region is an optimal choice because of their large rate capabilities.
Detector of Internally Reflected Cherenkov light (DIRC)
The DIRC detector is planned to be used as particle identification device. The particle traversing medium, with refraction parameter n, emits the photons in Θ angles in respect to movement direction where Θ = arccos(1/nβ) and β is the speed of the particle. Therefore by measuring the Θ angle one can determine the speed (β) of incident particle. Comparison of momentum (measured by other detectors) and speed lead to designation of the particle mass and its identification.
An example of the material, which suits for the Cherenkov light detector designed for the PANDA, is artificial quartz with the refraction index n=1.47 which enables the pion-kaons separation in momentum range 0.8-5 GeV/c.
Long quartz crystals of 1.7 cm thickness surround the STT detector. The light will travel along the crystal and it will be distributed over micro-channel plate photomulti- plier tubes via dedicated lenses.
Exactly the same concept is foreseen for the forward DIRC disk which will be 2 cm thick and it will have a radius of 110 cm. It will be positioned directly upstream of the forward end-cap calorimeter.
Ring Imagine Cherenkov light
In order to make possible π/K and K/p separation in a broad momentum region (2-15 GeV/c) the Ring Imagine Cherenkov detector is proposed to be placed in forward direction (below 220). It is planned to use similar construction to the HERMES RICH [10] and even to reuse parts of it. The detector will consist of two symmetrical parts: lower and upper. The incident particles will go through aluminum window, they will enter silica aerogel (with n=1.0304) and later the C4F10 gas (n=1.00137). The photons emitted in two different materials will be later reflected by a spherical mirror array located at the end. The light cones will be focused onto a focal surface located above and below the active volume. In case of the HERMES RICH the focal surface is covered almost completely (∼ 92% ) by the light collecting funnels ended with the photomultipliers.
Muon detector
The Drell-Yan processes, D-meson decays and J/ψ decays can be examined by the detection of the primary muons. The challenge for the muon detection is very high background coming from pions and decay muons. By applying filters and by looking for the correlation of the signals from all independent systems one should achieve desirable level of signal purity for muons. Mentioned correlations become more important especially with the lower beam energy.
The muon detection system will consist of four components: a Muon Barrel which will surround the TS, a Muon End Cap which will close the TS downstream of the target, a Muon Filter which will be situated right after the end cap and a Muon Range System which will be placed at the end of the FS.
The general detection concept of all PANDA muon systems is similar for all its components and it will be based on rectangular aluminum Mini Drift Tubes (MDT) interleaved with the iron absorber. In the TS the total number of 2751 MDTs for Muon Barrel and End Cap and 424 MDTs for the Muon Filter is foreseen to be used. In the End Cap more material is needed for absorbtion due to the higher momenta of the incident particles.
The main task of the Muon Range System is the discrimination of pions from muons and detection of pion decays. Additionally energy determination of neutrons and anti- neutrons with moderate resolution will be possible. The Muon Range System will have 576 MDTs and it will be placed 9 m downstream from the target.
Central Straw Tube Tracker (STT)
The STT will have a cylindrical shape and is planned to be placed at -550 mm to 1100 mm in z-direction relative to the target. It will have an inner radius of 150 mm and
the outer one of 420 mm. It will consist of 4224 straw tubes of 10 mm diameter and 1500 mm length. More detailed description of the straw tubes can be found in 2.4.4. The whole STT will be made of 6 modules (one module is presented in figure 2.6 (left)). The first 8 layers of each modules will be placed parallel to the beam z-axis. Then there will be 4 double layers, the first and the third one skewed by 2.9o the second and the fourth one skewed by −2.9o. The module ends with 11 parallel straw tube layers with decreasing number of straws (see figure 2.4.4 (right)).
The STT module will be placed in the solenoid magnetic field to enable momentum determination of the particles crossing its sensitive volume. The skewed straws are needed to enable three dimensional trajectory reconstruction.
All the six modules of the STT will be fixed to an aluminum supporting frame. The gas will be supplied to the straw tubes from the one side going through one straw and returning through the another straw. Also the front end electronics will be attached from one side of the module.
FIGURE 2.6: Left: Photography of one STT module. Right: View of the STT from the beam direction. The red color indicates straw tubes skewed
by −2.9o whereas the blue by 2.9o.
Forward Tracker (FT)
The Forward Tracker is responsible for the reconstruction of the trajectories of the particles going in the forward direction at small Θ angles. It will consists of 6 stations distributed before the dipole magnet (2 pieces), inside (2 pieces) and after (2 pieces) the magnetic field (see table 2.1). Such a placement allows precise parametrization of the particles tracks bending inside the magnetic field.
Each station will be made of four double layers of the straw tubes. The first and the last layer are planned to be placed vertically whereas the two middle ones will be skewed by ±5o. The straws, included in the station, will be grouped in modules. Each module will have 32 straw tubes and it will be equipped with the individual power supply, gas system, high voltage and front end electronics. The individual modules allow easy replacement of malfunctioning parts of the detector.
The size of the tracking station placed before the dipole magnet will be 134 cm horizontally and 64 cm vertically. The further stations will have larger dimensions as indicated in the table 2.1. The total number of straws foreseen to be used in the
final installation amounts to 12224. In figure 2.7 the first and the second FT station is presented. The hole inside the station is foreseen for the beam pipe.
FIGURE 2.7: The model of the FT1 and FT2 station. The hole inside the module is planned for the beam pipe.
Tracking station z_min - z_max [mm] Active area
Number of straws width [mm] height [mm]
1 2954-3104 1338 640 4x288 = 1152 2 3274-3424 1338 640 4x288 = 1152 3 3945-4245 1782 690 4x384 = 1536 4 4385-4685 2105 767 4x448 = 1792 5 6075-6225 3923 1200 4x824 = 3296 6 6395-6545 3923 1200 4x824 = 3296
TABLE 2.1: Size, placement and number of straws in each FT station.
2.4.4 Straw tube trackers
The readout system presented in this thesis is considered as a common solution for the both tracking stations. Therefore, in order to understand requirements defined on the system, underlying principles of the straw tube detectors are introduced in next section in more details.
Principles of operation and construction of PANDA straws
The basic building block of the straw tube trackers, used in the PANDA, are the straw tubes which are cylindrical mini drift chambers filled with the over pressured gas mixture. In the center of a straw tube a 20 µm anode wire is stretched along the cylinder axis. The wall of the straw tube is made of aluminized Mylar foil of 27 µm thickness. The length of the tubes varies between: 150 cm used in the STT and 68 cm used in the FT. A single complete STT straw weighs 2.5 g. The figure 2.8 presents stages of the STT tube assembly together with its components. Ready tubes are glued together forming layers which are then used to form STT and FT detectors. The layers of the straws are self-supporting due to the filling by over pressurized gas. This is a very desirable fea- ture as it limits the supporting frame needed for the detector and therefore limits the radiation length.
The straw tubes are a good choice for the drift chambers construction as they posses the following advantages:
FIGURE 2.8: The straw tube construction on the example of STT tracker.
• tight arrangement of the straws resulting in mechanically robust system,
• very high spatial resolution of the reconstructed tracks (σ < 150µm),
• reliable electrostatic configuration with shielding walls of the straw tubes which protects other straws in case one is damaged,
• a high detection efficiency for a single particle hit (reaching 99% [11]),
• a capability of handling high hit rates (1-2 MHz per straw tube),
• a small radiation length (X/X0 ∼ 0.05%) resulting in negligible particle scattering.
A dedicated gas mixture, Ar : CO2 (90:10), is used for the straw tubes filling. The incident particle ionizes the gas molecules producing electron-ion pairs. The high voltage applied to the anode wire cause the electrons to drift towards the anode and the ions move toward the cathode wall. The electric signal which is induced on the anode by the moving charge is then captured by the front end electronics.
Due to the demand on the spatial resolution of the tracking detectors the gas mixture, used in the straws, should enable a high amplitude anode signal even for single electron cluster. Unfortunately a high gas gain (closely connected with the high voltage) reduces the life time of the chambers and therefore a balance between performance and durability has to be found. Improper straws filling may also lead to electrons quenching or their velocity saturation preventing them from creating electron showers in the anode vicinity. Having in mind all the mentioned considerations the simulation was performed and the results have pointed to Ar : CO2 (90:10) gas mixture [11]. The properties of the mixture components are give in the table 2.2.
The number of created electron-ion pairs, during the ionization, depends on the energy loss of the incident particle. Using the Bethe-Bloch formula it can be shown that the energy deposition of the minimum ionizing particles (MIP) in the Ar : CO2
(90:10) equals 2.5 keV/cm at standard temperature and pressure. As straw tubes operate at 2 bars therefore the energy loss of incident particle equals 5 keV/cm. The interaction with the gas atoms leading to electron-ion pairs creation is called primary ionization. The primary ionization depends on incident particle characteristics (energy and charge) and gas properties (atomic number, density, ionization potential of the gas). The ionization caused by the primary electron-ion pairs is called secondary
Gas Ex [eV] Ei [eV] Wi [eV] dE/dx [keV/cm] Np cm−1 Nt cm−1 X0 m Ar 11.6 15.7 26 2.44 23 94 110
CO2 5.2 13.7 33 3.01 35.5 91 183
TABLE 2.2: Properties of the argon and the carbon dioxide. Ex and Ei
are the excitation and ionization energies. Wi is the minimal energy necessary to produce one electron-ion pair in the gas. dE/dx is the most probable energy loss of the minimum ionizing particle in the gas. Np
and Nt are the number of primary and total electrons per cm, respectively. X0 is the radiation length. Adapted from [12].
ionization. The total number of the primary electron-ion pairs can be calculated as nt = E/W where E is the energy deposition in the gas volume and W is the average effective energy necessary to produce one pair. Taking the values from the table 2.2 one can estimate the number of total ionization pairs to ' 94 cm−1 [13] and ' 188 cm−1 for the 2 bar over-pressure present inside the PANDAs’ straw tubes and the MIPs.
The electrons created in the ionization process move randomly and collide with the gas molecules with an average thermal energy 3
2kT ' 0.035eV . Once the electric field is applied the electrons and ions gain additional velocity towards the anode and the cathode respectively. The electrons move through the gas and lose part of their energy in the collisions with the molecules. As the mass of the electron is small in respect to the mass of the molecule the energy loss in the impact is small in contrast to the ions colliding with the molecules. Therefore the electrons velocity is higher (104 times) than the one of ions whose relatively slow motion contributes to the analog signal in form of a long tail (1 µm). The figure 2.9 shows results of the simulation of the drift time in respect to the distance from the anode wire for the PANDA straw. In case of magnetic field absence the maximal drift time, corresponding to the ionization close to the cathode wall (5 cm), equals 130 ns.
FIGURE 2.9: Simulated drift time in respect to the distance from the anode wire without (left) and with (right) magnetic field presence.
Adapted form [14] .
If the straw tube is placed in the magnetic field then the movement of the electrons is affected by the Lorenz force causing bending of the drift path and increase the maximal drift time. The behavior of the electrons has been simulated [14] and their paths inside
the tube, with and without magnetic field applied along the wire, are presented in figure 2.10.
FIGURE 2.10: Simulated drift path of the electrons originating form the ionization process. The case without (left) and with (right) magnetic
field is presented. Adapted form [14].
The ∼200 (more precisely 188, what was shown before) electrons coming from the ionization, caused by the minimum ionizing particles, posses the charge of 3.2×10−17C which is far below the detecting threshold of the electronics. For that reason a high voltage is applied to the anode wire which induces the electric field inside the straw tube. The intensity of the field increases dramatically close to the anode wire what causes the electrons to create a secondary electron showers multiplying the total charge. The capability of the charge multiplication is called detector gain and is described for the PANDA by the following formula:
G = e0.009U−5.3525
where U (in units V) denotes the high voltage applied to the anode wire. This function will be used later in the chapter 5 to estimate the total charge deposited by the radioactive sources or particles.
Purpose of the tracking system
As it was mentioned before, the tracking system will consist of MVD, STT and GEM subdetector systems in the Target Spectrometer and the FT in the Forward Spectrome- ter. There are three main goals of the tracking system:
• Vertex reconstruction - the determination of the primary vertex is crucial for identification of the particles which disintegrate into a couple of product particles.
• Momentum measurement - the precise particle trajectory reconstruction is the key to determine the momentum of a charged particle by measurement of its bending in the magnetic field.
• Energy loss measurement for the particle identification.
The particle identification based on the energy loss measurement which will be done mainly in the STT detector by means of 27 straw tube layers (energy measurements). For the PANDA the distinction between π and e/K/p and between K and p
should be possible in the momentum range below 800 MeV/c. In the [11] the separation power between two particles, assuming Gaussian distributions for dE/dx distribution, has been defined as:
S = |E1 − E2| σ1/2 + σ2/2
. (2.1)
The simulation of the STT has been performed to check what is the expected separation power for the different particle couples in the low energy regime. The results, which clearly demonstrates the particle identification capabilities of the STT, are shown in figure 2.11.
FIGURE 2.11: Separation power in the STT detector for the energy bands built with particles all tracked with the same muon mass hypothesis.
Source: [11].
Data rates in the straw tube trackers
The design of the straw tube trackers readout should be well suited to the hit rates in the detector. The simulations show that in the high luminosity mode the event rate will reach up to 2× 107 s−1. From the point of view of the readout load the interesting parameter is the number of straw tube responses per second, which can be defined as intensity. The intensities for individual straws will vary depending on the straw location. For the STT straws the simulation of the average hit probability, per straw unit length per event for the most inner layer, is presented in figure 2.12. The simulation was performed assuming p− p collisions at 15 GeV/c. In order to roughly estimate the intensities, which will occur on individual straws, one can estimate the average hit rate per straw as:
150[cm] ∗ 0.3 ∗ 10−3 ∗ 2 ∗ 107 = 0.9MHz
where 0.3 ∗ 10−3 was taken from figure 2.12 as the average number of hits per event and per cm.
-40 -20 0 20 40 60 80 100 0
0.1
0.2
0.3
0.4
0.5
0.6
1 layer, 2 atm
FIGURE 2.12: Simulation of pp reactions at 15GeV/c giving the number of hits per event and per cm along the tubes in the inner most layer of
the STT PANDA [11].
Also for the FT the simulation of intensity per straw was performed assuming the high luminosity mode. The result for all six tracking stations is shown in figure 2.13. Smaller counts number per second close to the x=0 is caused by the beam hole presence. The average intensity for the FT1-2, FT3-4 and FT5-6 equals 350, 310, 90 kHits/s/straw and was obtained by integration of the 2.13 for each station and dividing the result by the number of straws in the layer (for more details of straw number see table 2.1).
FIGURE 2.13: Number of counts per second expected in the individual straws placed in the X location.
Chapter 3
Architecture of the Readout System for the straw tube trackers
3.1 Data acquisition systems in nuclear and particle physics
The times when progress in physics could be achieved in small laboratories with no use of complex electronic devices has ended many years ago. Nowadays the mod- ern experiments in physics (not only in nuclear and particle physics) are carried out with great help of most up-to-date technologies, which deliver advanced sensors, data transmission protocols and means for processing and storage of large data volumes. Computers help scientists to analyze the data and conclude about investigated physic cases.
The general organization of a system which consists of detector sensors, signal processing chain (analogue and digital), data storage and some logic units which decide to store or abort given event is called Data AcQuisition - DAQ. The DAQ systems can be understand as small, compact device, like for example personal health monitoring or as a large scale system, like a power plant control and monitoring. In case of nuclear and particle physics DAQ systems are very complex. Its exact form depends on many aspects of undertaken experiment (e.g. scale, physical phenomena to be investigated) but it always consists of:
• detectors, which are sensors sensitive to particles (neutral or charged),
• amplifiers and shapers, which are electronic circuits that amplify and change the signal originating from the detector, to convenient form for further processing,
• digitizers, which translate the analog signal to its digital representation,
• data concentrators / data transmitters, which forward the data from digitizers to a data storage,
• trigger logic units which decide if given event should be stored or rejected,
• event building combined with a data storage.
Each part of the DAQ is described in more details in sections below.
3.1.1 Detector
A sensor, sometimes called a transducer, converts interaction of a particle with a detector material into a measurable electrical signal. The type of sensor defines its electrical output which can be any electrical attribute that varies over time (e.g. voltage, current, resistance). Most of the detectors require additional components and circuitry to properly produce a signal (e.g. application of high voltage).
23
24 Chapter 3. Architecture of the Readout System for the straw tube trackers
In case of nuclear and particle physics we can follow [15] which defines several considerations regarding choice of a detector for defined purpose. These are:
• Sensitivity It defines a capability of a detector to produce measurable signal for a given type of radiation and energy range. Some detectors are prepared to register charged particles and they cannot register particles with neutral charge (are not sensitive to neutral particles). In order to register neutral particles (for example photons or neutrons) one utilizes interactions which results in production of charged particles. If energy of particles is beyond the range specific for sensitive volume of the detector then the measured signal from the detector may be too small for efficient detection.
• Type of detector response Beside measuring an event of the irradiation by ionization of the sensitive volume, most of detectors are also able to give information about the amount of ionization which is proportional to the impact energy of the particle. In most of the cases, the signal which is obtained from the detector is a current pulse. A correlation between the amplitude of that pulse and the energy deposited by a particle passing sensitive volume is called detector response. It is desired that the response function is linear (or almost linear) in whole operation range of the detector, which gives equal conditions of measurement for different particles.
• Energy, time resolution The energy and the time resolution are quantities which characterize ability of a detector to disti

Development and evaluation of a signal analysis and a ...

Documents

Transcript of Development and evaluation of a signal analysis and a ...