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24 CHAPTER 1. INTRODUCTION + + + + + + + + + + + + + + E o + a) b) + + + + + + + + + + + + + + - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + - - + + + + + + + + - + - - - - - + - + + + c) - - - - - - - - + + - - - - - - - d) i + + + - - - - + - + + + + - + - - - - Figure 1.7: A schematic image of the development of a streamer in an RPC. a) An avalanche is developing as in Fig. 1.6. b) The avalanche charges lead to a high field detoriation in the gas gap. Moreover, photons start to contribute to the avalanche development and cause a rapid spread of the avalanche: A streamer evolves. c) A weak spark may be created. The local electrode area is discharged. d) The electric field is strongly decreased around the spot of the avalanche. The detector has a blind spot. Streamer Mode RPCs Single and double gap RPCs operated in streamer mode have so far found application in high energy physics experiments like L3 at CERN [41], BABAR at SLAC [42] and BELLE at KEK [43]. Future applications will include the ARGO experiment at the YangBaJing high altitude cosmic ray laboratory [44] and the OPERA [45] and MONOLITH [46] experiments at LNGS. The muon arm of the ALICE experiment at CERN [47, 48] will also be equipped with streamer mode RPCs. As the streamer signals are quite large (between 50 pC [49] and a few nC ([50]), no preamplification is needed and the signals can be discriminated directly. Thus the read out of streamer mode RPCs is quite simple [51, 52]. Double gap chambers operated at electric fields of 40 kV/cm in streamer mode and with 2 mm wide gaps reach efficiencies of 99% and a time resolution around 1 ns. However, the rate capability is limited to a few hundred Hz/cm 2 .
1.4. TRIGGER RPCS AND THEIR APPLICATIONS 25 Avalanche Mode RPCs The counting rate capability of RPCs is significantly improved if the occurrence of streamers is suppressed and the detector is operated in avalanche mode [53]. This can be achieved by the addition of small contents of SF6 to the gas mixture [39]. RPCs operated in avalanche mode will be used for the muon trigger systems of the ATLAS [54] and CMS [55] experiments at CERN. Multi gap Timing RPCs [56, 57] are implemented in the HARP experiment at CERN [58] and will equip the 176 m 2 TOF barell of the ALICE experiment [33]. Because the average pulse charges are a factor ten lower than in streamer mode, the avalanche mode allows to operate this device at a larger particle rate up to a few kHz/cm 2 [49], but it also makes it necessary to introduce low noise electronics. In this <strong>thesis</strong> we will focus on avalanche mode RPCs. There exist two different designs of RPCs: the Trigger RPC and the Timing RPC. Their performance is described in more detail in the following sections. 1.4 Trigger RPCs and their Applications The Large Hadron Collider (LHC) [60], currently being built at CERN in Geneva, Switzerland, will provide particle physics with the first laboratory tool to access the energy frontier above 1 TeV. Protons will be accelerated and stored at 7 TeV in two separate beam pipes, colliding with an unprecedented luminosity of 10 34 cm −2 s −1 at 40 MHz. In each pipe 2808 counter rotating bunches of approximately 75 mm length and a radius of about 16 µm contain around 10 11 protons each. The superconducting LHC dipoles occupy about 2/3 of the LHC tunnel circumference and provide a dipole field of 8.4 T strength. An image of the LHC and the positions of the four LHC experiments ATLAS [61], CMS [62], ALICE [63] and LHCb [13] is shown in Fig. 1.8. High momentum final state muons are amongst the most promising signatures of physics at proton-proton collisions at the LHC. To exploit this potential, the currently built high energy physics experiments ATLAS and CMS will comprise large area muon systems [54, 55] dedicated to detecting the muons. As an example Figs. 1.9 and 1.10 show the ATLAS detector system, that will be taking data starting in 2007 at the LHC. Resistive Plate Chambers with 2 mm gap size operated in avalanche mode are used in the ATLAS muon system. The RPCs are implemented on an area of 3650 m 2 and with 355.000 independent read out channels to provide information on the presence and arrival time of muons; they are used for triggering on muons. The simultaneous presence of four muons could reveal the decay of the sought after Higgs particle H that might be created in the proton-proton collisions at the LHC. In the high Higgs mass range mH > 130 GeV the so-called ‘gold-plated’ channel H → Z + Z → µ + +µ − +µ + +µ − has relatively small background. The LHC bunch crossing interval
Page 1 and 2: Detector Physics of Resistive Plate
Page 3 and 4: Zusammenfassung Widerstandsplattenk
Page 5 and 6: Abstract Resistive Plate Chambers (
Page 7 and 8: Contents 1 Introduction 1 1.1 Parti
Page 9 and 10: CONTENTS vii 7.2.3 Total Charge Den
Page 11 and 12: List of Figures 1.1 Schematic image
Page 13 and 14: LIST OF FIGURES xi 6.11 Simulated i
Page 15 and 16: Chapter 1 Introduction Resistive Pl
Page 17 and 18: 1.1. PARTICLE PHYSICS AND EXPERIMEN
Page 23 and 24: 1.2. INTERACTIONS OF PARTICLES WITH
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Page 45 and 46: 1.6. SUMMARY 31 on the Time-Of-Flig
Page 47 and 48: Chapter 2 Detector Physics of RPCs
Page 49 and 50: 2.1. GAS IONIZATION BY FAST CHARGED
Page 51 and 52: 2.2. ELECTRON DRIFT AND MULTIPLICAT
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Page 73 and 74: 2.5. STREAMERS 59 Figure 2.20: A me
Page 75 and 76: 2.6. SUMMARY 61 per cluster follows
Page 77 and 78: Chapter 3 Monte Carlo Avalanche Sim
Page 79 and 80: 3.1. THE 1-D MODEL 65 Avalanche Siz
Page 81 and 82: 3.2. THE 1.5-D MODEL 67 3. The prim
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3.2. THE 1.5-D MODEL 75 number of c
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3.3. THE 2-D MODEL 77 where δt is
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3.3. THE 2-D MODEL 79 Er(r, z, r
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3.3. THE 2-D MODEL 81 y r E Er θ x
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3.4. THE 3-D MODEL 83 The charge in
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3.4. THE 3-D MODEL 85 Electrons a)
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Chapter 4 Geometries and Typical Op
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RPC gas q [mm] g [mm] εr EW [/mm]
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The values shown in Table 4.3 are r
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Chapter 5 Results Obtained with the
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5.1. EFFICIENCY AND TIME RESOLUTION
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5.2. CHARGE-TO-TIME CORRELATION 97
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6.1. SIGNAL RISE TIME 101 induced c
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6.2. CHARGE SPECTRA 103 counts 10 3
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6.2. CHARGE SPECTRA 105 charges/ste
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6.2. CHARGE SPECTRA 107 The differe
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6.2. CHARGE SPECTRA 109 counts/35fC
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6.2. CHARGE SPECTRA 111 charges/ste
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6.3. OPERATIONAL MODE OF RPCS 113 t
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6.4. CHARGE-TO-TIME CORRELATION 115
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6.5. AVALANCHES IN PURE ISOBUTANE 1
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6.6. STREAMERS 121 a) b) electrons
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7.1. COMPARISON OF THE DIFFERENT MO
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7.2. AVALANCHES IN C2F4H2/ I-C4H10/
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7.4. SUMMARY 151 (e) The total elec
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7.4. SUMMARY 153 contracted at thei
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Chapter 8 Conclusions and Outlook C
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Appendix A Differential Collision C
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A.4. SCATTERING OF MASSIVE SPIN 1 P
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Appendix B Überblick Widerstandspl
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B.1. MOTIVATION FÜR DIE ARBEIT 163
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B.2. DETEKTORPHYSIK VON RPCS 165 i(
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B.4. SCHLUSSFOLGERUNG UND AUSBLICK
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Bibliography [1] W. Riegler, R. Vee
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BIBLIOGRAPHY 171 [29] V. Parchomchu
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BIBLIOGRAPHY 173 [59] E. Keil. The
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BIBLIOGRAPHY 175 [88] P. Fonte. App
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Danksagung Während der Dissertatio
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Curriculum Vitae Persönliche Infor
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