Measurement of Angular Correlation in b Quark Pair Production at the LHC as a Test of Perturbative QCD

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 avor creation, avor excitation, and gluon splitting. These three mechanisms produce b b pairs with characteristic kinematic behavior, which contribute dierently to the shape of the dierential b b production cross section with respect to the dierence in the azimuthal angle and the combined separation variable R = p 2 + 2 between the beauty and antibeauty quarks ( b and b , respectively); with being the change in the pseudorapidity = ln ( tan ( = 2)), being the polar angle. These and R variables are collectively referred to as angular correlation variables and hence forth referred to as A . By measuring the shape and absolute normalization of the dierential production cross section distributions with respect to A a test of the predictions of perturbative QCD can be performed. This dissertation describes a measurement of the dierential production cross sec- tions with respect to the A 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 identied as originating from b quarks, i.e. b-tagged, based on the presence of high impact param- eter 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 dierential production cross sections probed in this study is given by the requirement of two b-tagged hadronic jets with p jet T > 30 GeV and jet < 2 : 4, with an angular separation of R > 0 : 6 between them, one of these jets has a muon within its constituents with p T > 8 GeV and j j < 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 dierential cross sections within uncertainties.