Dissertation/Thesis Abstract

Measurement of Angular Correlation in b Quark Pair Production at the LHC as a Test of Perturbative QCD
by Dorney, Brian Lee, Ph.D., Florida Institute of Technology, 2013, 181; 3572589
Abstract (Summary)

Beauty quarks are pair-produced by strong interactions in multi-TeV proton-proton (pp) collisions at the CERN Large Hadron Collider (LHC). Such interactions allow for a test of perturbative Quantum Chromodynamics (QCD) in a new energy regime. The primary beauty-antibeauty quark b b pair production mechanisms in perturbative QCD are referred to as flavor creation, flavor excitation, and gluon splitting. These three mechanisms produce bb pairs with characteristic kinematic behavior, which contribute differently to the shape of the differential b b production cross section with respect to the difference in the azimuthal angle Δ&phis; and the combined separation variable Δ R = [special characters omitted] between the beauty and antibeauty quarks (b and b, respectively); with Δη being the change in the pseudorapidity η = — ln (tan (&thetas;/2)), &thetas; being the polar angle. These Δ&phis; and ΔR variables are collectively referred to as angular correlation variables and hence forth referred to as Δ A. By measuring the shape and absolute normalization of the differential production cross section distributions with respect to ΔA a test of the predictions of perturbative QCD can be performed.

This dissertation describes a measurement of the differential production cross sections with respect to the ΔA between two hadronic jets arising from the hadronization and decay of b or b (referred to as b hence forth) produced in pp collisions at the LHC observed with the Compact Muon Solenoid (CMS) detector. Hadronic jets are identified as originating from b quarks, i.e. b-tagged, based on the presence of high impact parameter tracks with respect to the primary pp interaction point in events in which a muon is also produced. The study presented in this dissertation corresponds to an integrated luminosity of 3 pb -1 collected in 2010 by the CMS experiment at a center-of-mass energy of 7 TeV.

The visible kinematic phase-space of the differential production cross sections probed in this study is given by the requirement of two b-tagged hadronic jets with [special characters omitted] > 30 GeV and ∥ηjet∥ < 2.4, with an angular separation of ΔR > 0.6 between them, one of these jets has a muon within its constituents with [special characters omitted] > 8 GeV and ∥ημ∥ < 2.1. The results obtained in data are compared with predictions based on perturbative QCD calculations given by CASCADE, MADGRAPH/MADEVENT, and PYTHIA Monte Carlo event generators. The predictions of perturbative QCD are found to be in agreement the measured differential cross sections within uncertainties.

Indexing (document details)
Advisor: Baarmand, Marc
Commitee: Abdulla, Ugur, Batcheldor, Daniel, Hohlmann, Marcus, Zhang, Ming
School: Florida Institute of Technology
Department: Physics and Space Sciences
School Location: United States -- Florida
Source: DAI-B 74/12(E), Dissertation Abstracts International
Subjects: Quantum physics, Physics, Particle physics
Keywords: Angular correlation, Perturbative QCD, Quantum chromodynamics, b quark pair production, b-tagging
Publication Number: 3572589
ISBN: 978-1-303-35149-5
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