The CMS Silicon Strip Tracker (eBook)

Dr. Oliver Pooth completed his postdoctoral lecture qualification at the RWTH Aachen University. He is a member of the CMS collaboration and now works as a private lecturer at the 3rd Physics Institute B at the RWTH Aachen University.

Preface 7
Contents 9
List of Figures 10
List of Tables 14
1 Introduction 15
1.1 The LHC project 15
1.2 The LHC physics programme 20
1.3 The CMS experiment 22
1.3.1 The muon spectrometer 26
1.3.2 The magnet 28
1.3.3 The calorimeter system 28
1.3.4 The inner tracking system 30
1.3.5 The trigger system 32
2 Semiconductor Detectors 34
2.1 The p-n junction 36
2.2 Signal creation 40
2.2.1 Detector types 42
2.3 Radiation effects 49
3 The CMS Silicon Strip Tracker 51
3.1 Tracker concept 51
3.1.1 Layout of the silicon tracker 54
3.2 Silicon strip detector modules 56
3.2.1 CMS Silicon Sensor 56
3.2.2 Mechanics 59
3.2.3 Readout Hybrids 63
3.3 Readout, triggering and services 65
3.3.1 On-detector module readout electronics 67
3.3.1.1 The APV25-S1 readout chip 67
3.3.1.2 The multiplexer chip, APVMUX 71
3.3.1.3 The Tracker Phase Locked Loop chip, TPLL 71
3.3.1.4 The Detector Control Unit chip, DCU 72
3.3.2 Off-detector module readout electronics 73
3.3.2.1 Optical links 73
3.3.2.2 The front-end driver 74
3.3.2.3 Services 75
3.3.2.4 Slow control and triggering 76
3.3.2.5 Summary 77
3.4 Radiation hardness 78
3.5 Tracker substructures 79
3.5.1 Tracker Inner Barrel and Tracker Inner Disks 80
3.5.2 Tracker Outer Barrel 82
3.5.3 Tracker End Caps 85
3.6 Laser Alignment System 92
3.7 Cooling system 93
3.8 Material budget 94
3.9 Expected performance 95
4 Detector Production and Commissioning 99
4.1 Production 99
4.1.1 Module production 102
4.1.1.1 Quality control during production 105
4.1.1.2 Summary of TEC module production 115
4.1.2 Petal production 118
4.1.3 Substructures 122
4.1.3.1 TIB/TID 124
4.1.3.2 TOB 126
4.1.3.3 TEC 127
4.2 Commissioning experiences 128
4.2.1 Magnet test and cosmic challenge 129
4.2.2 Tracker slice test 133
5 Conclusion 141
Bibliography 142

Semiconductor Detectors (p. 21-22)

Particle detectors based on semiconducting materials are used in a wide range of applications in various physics ?elds. The two main applications are tracking of charged particles and the precise energy spectroscopy of photons. Since the 1950s p-n junctions are used to detect signals from charged particles and photons traversing the depletion zone between an n-doped and p-doped material. For 25 years in coincidence with the detection of short lived mesons containing charm and bottom quarks and the study of decaying tau leptons, the particle physics community developed great interest in very fast particle detectors with high resolution. First applications of semiconducting particle detectors in high energy physics experiments date back to the 1970s.

Today nearly every large scale high energy physics experiment makes use of silicon strip and/or silicon pixel detectors to precisely determine the trajectories of traversing charged particles. The tracking device of the CMS experiment with a sensitive silicon area of approximately 200m2 is the largest project of this type today. The principle of operation of semiconductor detectors is similar to an ionisation chamber but is based on solid state material. Compared to the low density of the counting gas in gaseous detectors, semiconductor detectors are able to measure particles with higher material densities. In tracking applications the segmentation of electrodes allows a ?ner separation of the detection cells and therefore higher spatial resolution compared to gaseous detectors.

Charged particles or photons create electron hole pairs in the semiconductor material. Inside an electric ?eld the produced charge carriers are collected and converted to an electric signal that can be ampli?ed and shaped into the appropriate needs. Compared to the counting gas in gaseous detectors the average energy necessary to produce an electron hole pair in a semiconductor is one order of magnitude smaller (2.8 eV for germanium, 3.6 eV for silicon).

Because of the small energy gap between valence band and conduction band (0.67 eV for germanium, 1.14 eV for silizium) the detectors are often operated below room temperature to reduce the effect of thermal noise. Basic properties of silicon are summarised in table 2.1. As the amount of energy required to create an electron-hole pair is known, and is independent of the energy of the incident radiation, measuring the number of electron-hole pairs allows the determination of the energy of incident photons.

Energy spectroscopy is therefore possible using semiconductor detectors with excellent energy resolution compared to gaseous devices. Furthermore diamond based detectors [19] are an alternative to silicon detectors and are expected to offer better radiation hardness compared to silicon detectors. But today they are much more expensive and more dif?cult to produce even on a small scale.