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Performance of the ALICE Muon Spectrometer. Weak Boson Production and Measurement in Heavy-Ion Collisions at LHC

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Performance of the ALICE Muon Spectrometer. Weak Boson Production and Measurement in Heavy-Ion Collisions at LHC UNIVERSITE´ DE NANTES FACULTE´ DES SCIENCES ET TECHNIQUES ————- ECOLE´ DOCTORALE SCIENCES ET TECHNOLOGIES DE L’INFORMATION ET DES MATERIAUX´ N◦ attribue´ par la bibliotheque` Annee´ : 2007 Performance of the ALICE muon spectrometer. Weak boson production and measurement in heavy-ion collisions at LHC. THESE` DE DOCTORAT Discipline : Physique Nucleaire` Specialit´ e´ : Physique des Ions Lourds Pr´esent´eeet soutenue publiquement par Zaida CONESA DEL VALLE Le 12 juillet 2007, devant le jury ci-dessous Pr´esident K. WERNER, Professeur, Universit´ede Nantes, SUBATECH, Nantes Rapporteurs E. VERCELLIN, Professeur, Universita degli Studi di Torino, Torino D. G.-D’ENTERRIA ADAN, Charg´ede recherche, CERN, Gen`eve Examinateurs E. AUGE, Professeur, Universit´eParis-Sud XI, LAL, Orsay H. BOREL, Ing´enieurde recherche, CEA, Saclay Directeurs de these` : G. MARTINEZ GARCIA, Charg´ede recherche, CNRS, SUBATECH Nantes F. FERNANDEZ MORENO, Professeur, Universitat Aut`onomade Barcelona N◦ ED 366-312 Performance du spectrom`etre`amuons d’ALICE. Production et mesure des bosons faibles dans des collisions d’ions lourds aupr`esdu LHC. ——————– Performance of the ALICE muon spectrometer. Weak boson production and measurement in heavy-ion collisions at LHC. Zaida CONESA DEL VALLE SUBATECH, Nantes (France), 2007 Performance of the ALICE muon spectrometer. Weak boson production and measurement in heavy-ion collisions at LHC. TESIS DOCTORAL Zaida Conesa del Valle Directors de tesis: Gin´esMart´ınezGarc´ıa, SUBATECH Nantes Francisco Fern´andezMoreno, Universitat Aut`onomade Barcelona Grup de F´ısica de les Radiacions, Bellaterra (Spain), 2007 Contents Acknowledgements xi Abstract xiii I Introduction 1 1 Studying the Quark Gluon Plasma in Heavy Ion Collisions 3 1.1 From the Standard Model to the Quark Gluon Plasma .............. 3 1.1.1 Standard Model and Quantum ChromoDynamics ............ 3 1.1.2 Lattice QCD calculations ........................... 6 1.2 Probing the Quark Gluon Plasma in Heavy-Ion Collisions ........... 9 1.2.1 From AGS & SPS to RHIC and LHC .................... 9 1.2.2 Signatures: experimental observables ................... 11 1.2.3 Highlights from the SPS Heavy-Ion program ............... 12 1.2.4 RHIC results in a nutshell .......................... 13 1.3 Heavy quarks and quarkonia ............................ 16 1.3.1 Qualitative formation and decay times .................. 17 1.3.2 Quarkonia production in nucleon-nucleon collisions .......... 18 1.3.3 Production in a p-A collisions: cold nuclear effects ............ 19 1.3.4 Production in A-B collisions: hot nuclear effects ............. 20 1.3.5 Charmonium data interpretation: remarks ................ 22 1.3.6 Novel aspects of heavy flavor physics at LHC .............. 23 2 Weak bosons in hadron-hadron collisions 25 2.1 Qualitative formation and decay times ....................... 25 2.2 Why should we study weak bosons at LHC? ................... 26 2.3 Basics of the electroweak theory ........................... 27 2.3.1 Historical outline ............................... 27 vii Contents 2.3.2 Introduction to the electroweak theoretical formalism .......... 28 2.3.3 Particularities of the weak interaction ................... 29 II Experimental apparatus 33 3 The Experiment 35 3.1 The Large Hadron Collider ............................. 35 3.1.1 The beam travel road ............................. 35 3.2 The ALICE Detector ................................. 36 3.2.1 Global detectors ................................ 40 3.2.2 Central Barrel ................................. 44 3.2.3 Muon Spectrometer ............................. 50 4 Performance of the muon spectrometer: J/Ψ and high-pT muon measurements 59 4.1 Physics motivations .................................. 59 4.2 Basics of track reconstruction with the muon spectrometer ........... 60 4.2.1 Trigger decision ................................ 60 4.2.2 Reconstruction algorithm .......................... 63 4.2.3 Sources of inefficiency and various contributions to momenta resolution 64 4.3 Acceptance determination .............................. 68 4.3.1 The J/Ψ acceptance ............................. 69 4.4 Global efficiency evaluation ............................. 70 4.4.1 Unfolding the efficiency with an iterative method ............ 72 4.4.2 Results on dimuon pairs: the J/Ψ case ................... 75 4.4.3 Results on single muons ........................... 78 4.5 Factorized efficiency approach ........................... 83 4.5.1 Efficiency factorization in the muon spectrometer ............ 83 4.5.2 Results on dimuon pairs: the J/Ψ case ................... 85 4.5.3 Intrinsic tracking chambers efficiency ................... 87 4.5.4 Results on single muons ........................... 87 4.6 Remarks ........................................ 90 III Weak boson production 91 5 Weak boson production at the LHC 93 5.1 Generation of weak bosons at LHC energies .................... 93 5.1.1 Production physics processes ........................ 93 5.1.2 Generation with PYTHIA .......................... 99 5.2 Results on W boson production at LHC energies ................. 101 5.2.1 Proton-proton collisions at 14 TeV ..................... 101 5.2.2 Lead-lead collisions at 5.5 TeV ....................... 105 5.2.3 Proton-lead collisions at 8.8 TeV ...................... 106 viii Contents 5.3 Results of Z boson production at LHC energies .................. 110 5.3.1 Proton-proton collisions at 14 TeV ..................... 111 5.3.2 Lead-lead collisions at 5.5 TeV ....................... 113 5.3.3 Preliminary studies in argon-argon collisions at 6.3 TeV ......... 114 5.4 Remarks ........................................ 116 6 Weak boson measurement with the muon spectrometer 117 6.1 Muon sources at LHC energies ........................... 117 6.1.1 W and Z bosons decays ........................... 117 6.1.2 Beauty and charm muonic decays ..................... 120 6.1.3 Hadronic decays contribution ........................ 121 6.1.4 Drell-Yan contribution ............................ 122 6.2 Single muon pT distribution in hadron-hadron collisions ............ 122 6.2.1 Single muon measurement with the muon spectrometer ........ 125 6.2.2 Muon trigger conditions ........................... 130 6.3 Preliminary results on Z measurement feasibility ................. 131 6.4 Conclusions ...................................... 132 IV Discussion 135 7 Probing hot and dense QCD matter with high-pT muons at the LHC 137 7.1 Weak boson versus heavy quark production ................... 137 7.1.1 Production mechanisms ........................... 138 7.1.2 Nuclear parton distribution functions: nuclear shadowing ....... 138 7.2 Introduction to the theoretical treatment of heavy quark energy loss ...... 139 7.2.1 QCD factorization theorems ......................... 140 7.2.2 Medium induced gluon radiation ..................... 140 7.3 Are high-pT muons affected by the presence of a thermal medium? ...... 143 7.4 The W reference for high-pT single muon suppression .............. 145 7.4.1 Nuclear modification factor: RAA ...................... 147 7.4.2 Central versus peripheral nuclear modification factor: RCP ...... 150 7.4.3 Muon yield ratios ............................... 151 7.5 Outlook: Z bosons in heavy ion collisions ..................... 152 7.5.1 Z beauty decay channel ........................... 152 7.5.2 Z radiative decays .............................. 153 Conclusions 155 A Commonly used abbreviations 157 ix Contents B The front absorber influence on the measured track 159 B.1 Energy loss ....................................... 159 B.2 Straggling ....................................... 161 B.3 Multiple Coulomb scattering ............................ 161 C Parity violation on W decays 163 D Centrality determination: the Glauber model 165 D.1 Introduction ...................................... 165 D.2 Formalism ....................................... 167 D.2.1 Proton-nucleus (p-A) collisions ....................... 167 D.2.2 Nuclei-nuclei (A-B) collisions ........................ 168 D.2.3 ”Hard” collisions ............................... 170 D.2.4 Centrality dependence ............................ 174 Bibliography 177 Index 187 x Acknowledgments You are rewarding a teacher poorly if you remain always a pupil. F. Nietzsche There are lots of people I would like to thank for a huge variety of reasons. Though it is an almost impossible task, I am going to try anyway, and if your name is not listed, rest assured that my gratitude is not less than for those listed below. I would like to express my gratitude to J. Martino, B. Erazmus and Gines´ Mart´ınez Garc´ıa from SUBATECH and Francisco Fernandez´ Moreno from the Universitat Autonoma` de Bar- celona for giving me the opportunity to work with their groups. I am specially thankful to my mentor, Gines´ Mart´ınez Garc´ıa, for his support, guide and availability. He has always found the time and patience to discuss and to solve my doubts. His knowledge and personal qualities have been of great influence to me both professionally and personally. I am also in debt with the members of the Dimuon group at SUBATECH: to Christian Finck and to Laurent Aphecetche for their support and innumerable advices, and to the latest recruitments, Guillaume Batigne, Philippe Pillot and Nicolas LeBris. The last chapter of this work has been the fruitful result of the collaboration with Heng-Tong Ding, Andrea Dainese and Daicui Zhou, and partly the outcome of the teachings of Stephane´ Peigne.´ I wish to thank them all, and
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