Test of color dynamics and precision measurements of as using jet production in dis with zeus detector at hera

• Autores: Marcos Jiménez Belenguer
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2008
• Idioma: español
• Materias:
  • Física
    • Física teórica
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • 1 Introduction 1 1.1 Deep inelastic scattering and the parton model . . . . . . . . . . . . . 1 1.2 The Quantum Field Theory of Color Dynamics . . . . . . . . . . . . 5 1.2.1 Experimental verification of the gauge structure of QCD in e+e collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2.2 Loop corrections and the running of the strong coupling . . . 10 1.2.3 The scaling violations of the structure functions and the factorization property of QCD . . . . . . . . . . . . . . . . . . . 12 1.3 Jet measurements in NC DIS and determinations of ¿s(MZ) at HERA 18 1.3.1 The definition of a jet . . . . . . . . . . . . . . . . . . . . . . 22 1.3.2 The Breit frame of reference . . . . . . . . . . . . . . . . . . . 25 1.3.3 Extracting ¿s(MZ) from inclusive-jet measurements in NC DIS in the Breit frame . . . . . . . . . . . . . . . . . . . . . . 26 1.3.4 Three-jet cross sections in NC DIS in the Breit frame and angular-correlation variables . . . . . . . . . . . . . . . . . . . 28 2 The HERA collider and the ZEUS detector 33 2.1 The Hadron Electron Ring Accelerator . . . . . . . . . . . . . . . . . 33 2.2 The ZEUS Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 2.2.1 The Central Tracking Detector . . . . . . . . . . . . . . . . . 38 2.2.2 The Uranium-Scintillator Calorimeter (UCAL) . . . . . . . . . 40 2.3 The luminosity measurement . . . . . . . . . . . . . . . . . . . . . . . 42 2.4 The ZEUS trigger and data acquisition systems . . . . . . . . . . . . 43 2.5 Event reconstruction and analysis . . . . . . . . . . . . . . . . . . . . 44 2.6 Event and detector simulation . . . . . . . . . . . . . . . . . . . . . . 47 3 Theoretical calculations and event generators 49 ii CONTENTS 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 3.2 Theoretical predictions in pQCD . . . . . . . . . . . . . . . . . . . . 50 3.3 Sources of theoretical uncertainty in the cross-section predictions . . . 51 3.4 Sensitivity of the angular-correlation variables to the underlying symmetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 3.4.1 Additional sources of color dependence in the theoretical predictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67 3.4.2 A restricted phase-space region for the study of the angularcorrelation variables . . . . . . . . . . . . . . . . . . . . . . . 74 3.4.3 O(¿2 s) vs O(¿3 s) theoretical predictions for the three-jet angularcorrelations analysis . . . . . . . . . . . . . . . . . . . . . . . 82 3.5 Monte Carlo event generators . . . . . . . . . . . . . . . . . . . . . . 85 3.5.1 The parton cascade . . . . . . . . . . . . . . . . . . . . . . . . 87 3.5.2 Hadronization models . . . . . . . . . . . . . . . . . . . . . . 89 3.6 Detector Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 3.6.1 The LEPTO Monte Carlo generator . . . . . . . . . . . . . . . 91 3.6.2 Technical details of the samples generated for the angular correlations and ¿s analyses . . . . . . . . . . . . . . . . . . . . . 92 3.7 Comparisons of the MC parton level with DISENT and NLOJET++ 93 3.7.1 Theoretical uncertainties due to the parton cascade and hadronization models . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 4 Event selection and variable reconstruction 103 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 4.2 Data samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 4.3 Event selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 4.3.1 Online selection . . . . . . . . . . . . . . . . . . . . . . . . . . 105 4.3.2 Offline selection . . . . . . . . . . . . . . . . . . . . . . . . . . 107 4.4 Jet reconstruction using the UCAL . . . . . . . . . . . . . . . . . . . 111 4.4.1 Jet energy scale corrections . . . . . . . . . . . . . . . . . . . 112 4.4.2 Detector bias and resolution . . . . . . . . . . . . . . . . . . . 112 4.4.3 The Breit frame and the cut on cos ¿h . . . . . . . . . . . . . 114 4.5 Data and Monte Carlo distributions . . . . . . . . . . . . . . . . . . . 130 4.5.1 Comparisons of data and MC for the ¿s analysis using HERA I data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 CONTENTS iii 4.5.2 Comparisons between data andMC for three-jet angular-correlation distributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 4.5.3 Comparisons of data and MC for the ¿s analysis using HERA II data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 5 Correction factors and systematic uncertainties 153 5.1 Correction factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153 5.1.1 Acceptance correction factors . . . . . . . . . . . . . . . . . . 154 5.1.2 QED correction factors . . . . . . . . . . . . . . . . . . . . . . 155 5.1.3 Z0-exchange corrections . . . . . . . . . . . . . . . . . . . . . 156 5.1.4 Parton-to-hadron corrections . . . . . . . . . . . . . . . . . . . 156 5.2 Experimental uncertainties . . . . . . . . . . . . . . . . . . . . . . . . 169 6 Results: Jet radius dependence of inclusive-jet cross sections in DIS at HERA 183 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183 6.2 Differential inclusive-jet cross sections in NC DIS . . . . . . . . . . . 184 6.3 Determinations of ¿s(MZ) . . . . . . . . . . . . . . . . . . . . . . . . 197 6.3.1 The extraction of ¿s(MZ) from the inclusive-jet cross section measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . 197 7 Results: Angular correlations in three-jet production in NC DIS at HERA 221 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 221 7.2 Comparison to the MC simulations: CDM and MEPS . . . . . . . . . 222 7.3 Comparison to pQCD at O(¿2 s) and O(¿3 s) . . . . . . . . . . . . . . . 226 7.4 Comparison to O(¿2 s) predictions based on different symmetry groups 232 7.5 Discussion of an extraction of the color factors and conclusions . . . . 236 8 Summary and Conclusions 243 8.1 Inclusive-jet cross sections in NC DIS and determinations of ¿s(MZ) . 243 8.2 Angular correlations in three-jet events in NC DIS . . . . . . . . . . . 246 9 Resumen y Conclusiones 249 9.1 Secciones eficaces inclusivas de jets en NC DIS y determinaciones de ¿s(MZ) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249 9.2 Correlaciones angulares en sucesos con tres jets en NC DIS . . . . . . 252