A Study of Hadronic Punchthrough at the RD5 Experimental Setup VERBUM Lithograph, July 1942, 33.2 38.6 cm M.C. Escher's ªVerbumº c 1997 Cordon Art ± Baarn ± Holland. All rights reserved. A Study of Hadronic Punchthrough at the RD5 Experimental Setup Een wetenschappelijke proeve op het gebied van de Natuurwetenschappen. Proefschrift ter verkrijging van de graad van doctor aan de Katholieke Universiteit Nijmegen, volgens besluit van het College van Decanen in het openbaar te verdedigen op donderdag 10 april 1997, des namiddags om 3.30 uur precies, door Robert Bergman geboren op 1 april 1964 te Zwolle. Promotor: Prof. Dr. E.W. Kittel Co-promotor: Dr. A.C. KonigÈ Manuscriptcommissie: Dr. Ir. H. van der Graaf Dr. Ir. C.L.A. Pols ISBN: 90-9010437-2 Ter nagedachtenis aan Henk .... and eventually human beings arrived. The human beings were different primarily because they were the only species intensely curious about their surroundings. In time, mutations occured, and an odd subset of humans began roaming the land. They were arrogant. They were not content to enjoy the magni®cence of the universe. They asked "How?". How was the universe created? How can the "stuff" of the universe be responsible for the incredible variety in our world: stars, planets, sea otters, oceans, coral, sunlight, the human brain? The mutants had posed a question that could be answered - but only with the labor of millennia and with a dedication handed down from the master to student for a hundred of generations. The question also inspired a great number of wrong and embarrassing answers. Fortunately, these mutants were born without a sense of embarrassment. The were called physicists. ± Leon Lederman with Dick Teresi in 'The God Particle' [1] Contents 1 Elementary Particles 1 1.1 Introduction 1 1.2 Standard Model 2 1.2.1 Electroweak Interactions 3 1.2.2 Strong Interactions 4 1.2.3 Higgs Mechanism 5 1.3 Experimental Status 5 2 Large Hadron Collider 7 2.1 Experimental Particle Physics 7 2.2 LHC: Proton-Proton Collider 8 2.3 Detectors for LHC 9 2.3.1 ATLAS 11 2.3.1.1 Inner Detector in Solenoidal Magnetic Field 11 2.3.1.2 Calorimeter 12 2.3.1.3 Muon Detector in Toroidal Magnetic Field 12 2.3.1.4 Muon Spectrometer Performance 15 2.3.2 CMS 16 2.4 Physics at the LHC 17 2.4.1 Standard Model Higgs Boson 17 2.4.1.1 Higgs Boson Production 19 2.4.1.2 Higgs Boson Decays and Experimental Signatures 20 2.4.1.3 Four-Muon Decay Mode and its Backgrounds 22 2.4.2 Quark, Neutrino and Beyond SM Physics 25 3 Honeycomb Strip Chamber 27 3.1 Introduction 27 3.2 Charged Particle Detection 27 3.2.1 Energy Loss of Charged Particles 27 3.2.2 Energetic Knock-On Electrons 29 3.3 Motion of Charges in Gases 30 3.3.1 Electron and Ion Diffusion 30 3.3.2 Electron and Ion Drift 31 3.3.3 Drift in a Magnetic Field 32 3.3.4 Electron Attachment 34 i ii Contents 3.4 Ampli®cation of Ionization 35 3.4.1 The Proportional Mode and Beyond 35 3.4.2 Ampli®cation Factor in the Proportional Mode 38 3.4.3 The Signal Development 40 3.4.3.1 Signal Generation on the Anode 40 3.4.3.2 Signal Generation on the Cathode 41 3.5 Honeycomb Strip Chamber 41 3.5.1 Principle and Construction 41 3.5.2 Drift Time Measurement with the Anode Wire 42 3.5.3 Charge Ratio Measurement with the Cathode Strips 43 4 Tracking Calorimeter 45 4.1 Introduction 45 4.2 Sampling Calorimetry 46 4.3 Electromagnetic Showers 47 4.3.1 Interaction Processes 47 4.3.2 Shape of the Particle Shower 51 4.3.3 Energy Resolution 52 4.3.4 Sampling Calorimeter Response 53 4.4 Hadronic Showers 54 4.4.1 General Attributes 54 4.4.2 Dimensions of the Particle Shower 55 4.4.3 Calorimeter Performance 56 4.4.3.1 The eh Signal Ratio 56 4.4.3.2 Calorimeter Response 57 4.4.3.3 Compensating Hadron Calorimeter 58 4.4.3.4 Achieving Compensation 60 4.4.4 Energy Resolution 61 4.5 Tracking Calorimeter 62 4.5.1 Goals of the Tracking Calorimeter 62 4.5.2 Mechanical Construction of the HSC layers 64 4.5.2.1 Folding and Assembly of the Foil 65 4.5.2.2 Assembly and Wiring of a Single-Layer HSC 66 4.5.3 Assembly of the Calorimeter 68 4.5.4 TRACAL Readout Electronics 68 4.5.4.1 Wire Signals 68 4.5.4.2 Strip Signals 69 4.5.4.3 Calibration 70 5 Experimental Setup of RD5 73 5.1 Introduction 73 5.2 Beam Line for RD5 74 5.3 Description of the RD5 Detector 77 5.3.1 Magnets 79 5.3.2 Trigger 80 Contents iii 5.3.3 Beam De®nition 81 5.3.4 Tracking Calorimeter 82 5.3.4.1 Drift Time Measurement in TRACAL 82 5.3.4.2 Identi®cation of Electromagnetic Secondaries 85 5.3.5 Resistive Plate Chambers 88 5.3.6 Muon Drift Chambers 89 5.3.7 Data Acquisition System 90 6 Punchthrough Measurements 91 6.1 Introduction 91 6.2 Total Punchthrough Probability 91 6.2.1 Punchthrough Data Sample 91 6.2.2 Determination of Punchthrough Probability 93 6.2.2.1 Penetration Depth 93 6.2.2.2 Muon Background Subtraction 97 6.2.3 Description of RD5 Punchthrough Simulation 105 6.2.4 Results for Hadron-Induced Showers 106 6.2.4.1 Total Punchthrough Probability 106 6.2.4.2 Shower Lateral Distribution in TRACAL 112 6.2.4.3 Shower Multiplicity Distribution in TRACAL 113 6.3 Momentum and Angular Distribution of Punchthrough Muons 114 6.3.1 Determination of Punchthrough Muon Momentum 114 6.3.1.1 Momentum Fit of Punchthrough Muons 115 6.3.1.2 Description of Simulation 115 6.3.2 Momentum Distribution of Punchthrough Muons 116 6.3.3 Angular Distribution of Punchthrough Muons 120 6.4 Summary and Conclusions 122 A Physical Constants 123 B Acronyms 125 C Punchthrough Tables 127 Bibliography 133 Summary 141 Samenvatting 143 Dankwoord 147 Curriculum Vitae 149 1 Elementary Particles Nothing exists except 'atomos' and empty space; everything else is opinion. th ± Democritus ( century B.C.) 1.1 Introduction Elementary particle physics or high energy physics attempts to describe nature at a fundamental level. The objects of investigations are the ultimate constituents of matter, their interactions and the particles which mediate these interactions. For millenia mankind has tried to understand nature. A number of concepts still in use today were already introduced by the ancient Greek philosophers. For instance, the notion that matter consists of indivisible building blocks (atoms) was ®rst introduced by Democritus around B.C. About the same time Empedocles launched his vision that all materials were composed of only four ªelementsº: earth, water, air and ®re. Obviously the meaning and interpretation of these concepts has changed since the epoch of th the ancient philosophers. The atom was revitalised by the work of Dalton in the century. The role of the original four elements was replaced by almost a hundred chemical elements, culminating in the construction of the periodic table of the elements by Mendeleev in . The empty places in the periodic table belonged to elements still to be discovered. Based on their expected chemical properties some elements were indeed observed within a few years and proved the periodic table to be successful. Furthermore, the regularity of the periodic table suggested an underlying structure. It took the discovery of both the electron [2] and the atomic nucleus [3], together with the development of quantum mechanics to explain this structure. After the discovery of the neutron [4±6] also the composition of the nucleus became evident. The elementary particles needed to form the atoms of the chemical