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Production in Deep Inelastic Ep Scattering at Hera Measurement of inelastic J/y production in deep inelastic ep scattering at Hera Dissertation zur Erlangung des Doktorgrades des Fachbereichs Physik der Universitat Hamburg vorgelegt von Alexei Antonov aus Moskau Hamburg, 2007 Gutachter der Dissertation: Prof. Dr. R. Klanner JProf. Dr. J. Haller Gutachter der Disputation: Prof. Dr. R. Klanner Dr. A. Geiser Datum der Disputation: 27.07.2007 Vorsitzender des Prafungsausschusses: Prof. Dr. E. Heumann Vorsitzender des Promotionsausschusses: Prof. Dr. G. Huber MIN-Dekan des Fakultat Physik: Prof. Dr. A. FrUhwald Abstract This thesis presents a measurement of the inelastic production of J/-0 mesons in ep collisions with the ZEUS detector at HERA using an integrated luminosity of 109 pb -1. The J/^ mesons were identified using the decay channel J/0 ^ p +p-. The measurements were performed in the kinematic range 2 < Q2 < 80 GeV2, 50 < W < 250 GeV, 0.2 < z < 0.9 and -1.6 < Ylab < 1.3, where Q2 is the virtuality of the exchanged photon, W is the photon-proton centre-of-mass energy, z is the fraction of the photon energy carried by the J/0 meson in the proton rest frame and Yab is the rapidity of the J/0 in the laboratory frame. The measured cross sections are compared to theoretical predictions within the non-relativistic QCD framework including colour-singlet and colour-octet contributions, as well as to predictions based on the kT-factorisation approach. Calculations of the colour-singlet process generally agree with the data, whereas inclusion of colour-octet terms spoils this agreement. As a technical part of this thesis, the Straw-Tube Tracker (STT) GEANT simulation and track reconstruction software developed. Studies of the STT performance with MC data and real data presented. Kurzfassung Diese Dissertation beschreibt eine Messung inelastischer J/^-Meson-Produktion in ep Kollisionen mit dem ZEUS Detektor bei HERA unter Verwendung einer integrierten Luminositat von 109 pb -1. Die J/^-Mesonen wurden mit Hilfe des Zerfallskanals J/^ ^ p+identifiziert. Die Messungen wurden im kinematischen Bereich 2 < Q2 < 80 GeV2, 50 < W < 250 GeV, 0.2 < z < 0.9 und -1.6 < Yiah < 1.3 durchgefuhrt. Dabei beschreibt Q2 die Virtualitat des ausgetauschten Photons, W die Photon-Proton-Schwerpunktsenergie, z den Anteil der Photon Energie, die vom J/^-Meson im Ruhesystem des Protons getragen wird und Ylab die Rapiditat des J/-0 im Laborsystem. Die gemessenen Wirkungsquerschnitte werden mit theoretischen Vorhersagen der nicht-relativistischen QCD, unter Beracksichtigung von Farb-Singulett- und Farb- Oktett-Beitragen, wie auch mit Vorhersagen des kT-Faktorisierungsansatzes verglichen. Berechnungen des Farb-Singulett-Prozesses stimmen im Allgemeinen mit den Daten uberein, wahrend mit Einbeziehen von Farb-Oktett-Termen keine Ua bereinstimmung erreicht wird. Als technischer Teil dieser Arbeit wurde die Straw-Tube-Tracker (STT) GEANT-Simulation und Spurrekonstruktionssoftware entwickelt. Es werden Studien der STT-Leistung mit MC-Daten und echten Daten vorgestellt. Contents Contents Contents List of Figures iii 1 Introduction 1 2 Phenomenology of Charmonium Production 5 2.1 Charmonium ...................................................................................... 5 2.2 Deep Inelastic Scattering .................................................................... 8 2.3 DIS Kinematics ................................................................................... 9 2.4 Structure Functions ............................................................................. 11 2.5 Quark Parton Model .......................................................................... 12 2.6 Quantum Chromodynamics ............................................................. 13 2.7 QCD factorization and parton densities ........................................... 14 2.8 Parton Evolution ................................................................................ 15 2.8.1 DGLAP evolution .................................................................... 16 2.8.2 BFKL evolution and kT factorization .................................. 18 2.8.3 CCFM equation ....................................................................... 19 2.9 Charm Production in DIS................................................................. 19 2.9.1 Boson-Gluon-Fusion .............................................................. 20 2.10 Inelastic Charmonium production in DIS........................................ 21 2.10.1 The Color Evaporation Model.............................................. 21 2.10.2 The Color Singlet Model....................................................... 22 2.10.3 Non-relativistic QCD factorization method ......................... 23 i Contents 3 The ZEUS detector at HERA 27 3.1 The HERA collider............................................................................. 27 3.2 The ZEUS Detector............................................................................. 30 3.2.1 The Central Tracking Detector (CTD) ............................... 33 3.2.2 The Uranium-scintillator Calorimeter (UCAL).................. 36 3.2.3 The Muon Detectors ............................................................. 39 3.2.4 The Small Angle Tracking Detector (SRTD)..................... 44 3.2.5 The Hadron Electron Separator (HES)............................... 44 3.2.6 The Luminosity Measurement .............................................. 44 3.2.7 The ZEUS trigger system .................................................... 46 3.3 ZEUS Detector Simulation ................................................................. 51 4 Event reconstruction and data selection 53 4.1 Kinematic reconstruction .................................................................... 53 4.1.1 Electron method .................................................................... 55 4.1.2 Jacquet-Blondel method [94] ................................................. 55 4.1.3 Double angle method [95] 56 4.1.4 The E method [96] ................................................................. 56 4.1.5 The kinematic variables reconstruction ..................... 57 4.1.6 For this analysis ....................................................................... 57 4.2 Event reconstruction .......................................................................... 58 4.2.1 Track and vertex reconstruction ........................................... 58 4.3 Reconstruction of the hadronic system ........................................... 59 4.3.1 Hadronic energy flow reconstruction ..................................... 60 4.3.2 Corrections for the presence of muons .................................. 62 4.4 Identification and reconstruction of the scattered lepton ............... 64 4.4.1 Electron identification .......................................................... 64 4.4.2 Electron position reconstruction ........................................... 64 4.5 Muon reconstruction .......................................................................... 67 4.5.1 The BREMAT matching package ........................................ 67 4.5.2 The MV muon finder ................................................................. 70 4.6 E — cut.............................................................................................. 72 4.7 Trigger chain for online data selection .............................................. 73 4.7.1 First and second level trigger .............................................. 73 4.7.2 Third level trigger ................................................................. 75 4.7.3 The data samples .................................................................... 76 4.8 Offline data selection .......................................................................... 76 ii Figures 4.8.1 Selection of the neutral current DIS event sample ............ 76 4.8.2 J/^ reconstruction ................................................................. 78 4.8.3 Kinematic cuts....................................................................... 80 4.8.4 Further inelastic events selection ........................................... 82 4.8.5 Summary of the offline selection cuts and J/^ signal ... 83 4.9 Monte Carlo models ......................................................................... 86 4.9.1 Control plots and resolutions .............................................. 88 5 Inelastic J/-0 Production in DIS 93 5.1 Cross section measurement ................................................................. 93 5.2 Systematic uncertainties .................................................................... 99 5.3 Results......................................................................................................100 5.4 Conclusions ......................................................................................... 101 6 HERA II and the ZEUS Straw-Tube Tracker 107 6.1 The HERA luminosity upgrade ...........................................................107 6.2 The ZEUS upgrade ................................................................................ 108 6.3 The ZEUS Straw-Tube Tracker ...........................................................111 6.3.1 The STT detector....................................................................... 111 6.3.2 The STT readout electronics .....................................................113 6.3.3 The STT Monte-Carlo simulation ............................................114 6.3.4 The STT pattern recognition program STRECON................120 6.3.5 Study of the STT
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