Triple-Differential Measurement of the Dijet Cross Section at $\sqrt{s}$ = 13 TeV with the CMS Detector

Abstract

In light of the large quantity of data collected during the second operational run of the Large Hadron Collider (LHC) at CERN, which has made it possible to perform measurements at unprecedented energies with a high degree of statistical precision, the necessity of understanding and constraining the systematic effects on such measurements has become increasingly important. Precision measurements of jet observables in proton-induced collisions have proven instrumental in constraining the parton distribution functions (PDFs) which describe the internal structure of protons, and which remain one of the largest sources of uncertainty in many analyses performed at hadron colliders. This thesis presents the first triple-differential measurement of the dijet production cross section performed in proton-proton collisions at a center-of-mass energy of 13 TeV, based on a data sample of 35.9 fb$^{-1}$ recorded by the CMS experiment at the Large Hadron Collider at CERN. The cross section is measured using anti-$k_\text{T}$ jets with radius parameters of R = 0.4 and R = 0.8 as a function of the dijet rapidity separation $y^{*}$ , the total boost of the dijet system $y_\text{b}$ , and either the average transverse momentum $\langle p_\text{T}\rangle_{1,2}$ or the invariant mass $m_\text{jj}$ of the dijet system as the third variable. This choice of rapidity variables exploits the topology of the dijet system to achieve an increased sensitivity to the proton PDFs. After accounting for detector-induced systematic effects in a three-dimensional unfolding procedure, the measured spectra are compared to fixed-order theory predictions at next-to-next-to-leading order accuracy in perturbative quantum chromodynamics, obtained using several recent PDF sets. While the data are observed to be described by the theory within the experimental and theoretical uncertainties across a large portion of the phase space, potentially significant deviations are observed in areas where a heightened sensitivity to the PDFs is expected.