Measurement of the strong coupling constant using differential cross sections of the W boson produced in association with jets with the CMS detector at the LHC

Abstract

This Ph.D. thesis presents two analyses in the field of experimental particle physics. The first analysis is the precision measurement of the production cross section of a W± boson in association with jets in proton-proton collisions, as well as an investigation of the measurement of the strong coupling αs. The second analysis investigates the use of gas mixtures with reduced CF4 fractions in the Cathode Strip Chambers subsystem of the Compact Muon Solenoid experiment at the CERN Large Hadron Collider. The W+jets analysis uses data from the proton-proton collisions at a center-of-mass collision energy (√s) of 13 TeV collected by the Compact Muon Solenoid experiment during the Run 2 period (2016 - 2018) of the Large Hadron Collider, corresponding to a data sample with a total integrated luminosity of 137 fb−1. This analysis includes the measurement of cross sections differential in a number of observables including the jet transverse momentum (pT), the jet rapidity ( y ), and the azimuthal separation (∆φ) between the jet and the muon from the W boson decay, for two different jet multiplicities and two different jet definitions. The invariant mass of the two leading jets is studied as well. Angular correlations between jets are also measured, as well as the angular separation between the muon from the W boson decay and the closest jet. The measurements are compared to the theoretical predictions generated from Monte Carlo simulations that include matrix-element calculations at leading order and next-to-leading order accuracy in the QCD coupling, interfaced with parton shower simulations. The measured W+jets cross-sections may also be used to make a precision measurement of the strong coupling αs at the scale of the Z boson mass (MZ), and the final result of this study is currently under investigation. The second analysis investigates the longevity properties of a Cathode Strip Chamber detector operating using gas mixtures with different fractions of CF4, including gas mixtures with 5%, 2%, and 0% CF4. The data used in this analysis were taken at CERN. This analysis was done in order to investigate the potential decrease in the use of CF4 in the Cathode Strip Chamber subsystem for future operation, in the interest of reducing the environmental impact from operating the Compact Muon Solenoid experiment at the CERN laboratory.--Author's abstract