| Thesis | |
| Report number | CERN-THESIS-2023-431 |
| Title | Measurement of the associated production of a W boson and a charm quark in proton-proton collisions at $\sqrt{s}=13$ TeV with the CMS detector at the LHC |
| Translation of title | Medida de la producción asociada de un bosón W y un quark charm en colisiones protón-protón a $\sqrt{s}$ = 13 TeV con el detector CMS en el LHC |
| Author(s) | Sanchez Navas, Sergio (CSIC, Madrid) |
| Publication | 2023 - 139. |
| Thesis note | PhD : Madrid U. : 2023 |
| Thesis supervisor(s) | Fernández Ramos, Juan Pablo ; Hernández Calama, José María |
| Note | Presented 07 Jun 2023 |
| Subject category | Particle Physics - Experiment ; Detectors and Experimental Techniques |
| Accelerator/Facility, Experiment | CERN LHC ; CMS |
| Abstract | Scientific knowledge experienced an age of explosion during the XX century, fruitful in discoveries that radically changed the perspective we had of Nature. Our current quest is, however, to continue questioning the fundamental aspects of everything that surrounds us, to test until the very end how far the great theories can go, and to pursue with the undeniable task of human restlessness to answer the question ``and why is that?”. In the specific topic of this work, we will make use of the largest machine ever built to obtain information about some of the smallest elements of matter, measuring with the best precision up to date the cross section of a process that could shed some light on the mystery of fundamental asymmetry between matter and antimatter in the Universe. Our mind demands symmetry. The associated production of a W boson and a single charm quark (W+c) in proton-proton collisions at the LHC is directly sensitive to the strange quark content of the colliding protons at an energy scale of the order of the W boson mass. Studies of this process provide valuable information on the strange quark parton distribution function (PDF), which is one of the least constrained PDFs of the proton. Accurate measurements of the W +c production cross section and of the $\Rcpm = \sigma(W^++\bar{c})/\sigma(W^-+c)$ cross section ratio can probe the level of asymmetry between the s and $\bar{\text{s}}$ PDFs and help to measure their relative content with respect to the up and down antiquarks coming from the quark-gluon sea of the proton. A measurement of the associated production of a W boson and a charm quark in proton-proton collisions at a centre-of-mass energy of 13 TeV is reported. The analysis uses a data sample corresponding to a total integrated luminosity of 138 fb$^{-1}$ collected by the CMS detector at the LHC. W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm jets are tagged by the presence of a muon or a secondary vertex inside the jet. The W+c production cross section and the cross section ratio $\Rcpm$ are measured inclusively in a fiducial region of phase space, and differentially as a function of the transverse momentum and the absolute value of the pseudorapidity of the lepton from the W boson decay. We present the measurement of the W+c production cross section at $\sqrt{s}$ = 13 TeV in four independent selection channels: the decay of the W boson into electron or muon and a neutrino, and the identification of jets originated from a c quark through the reconstruction of a muon (SL) or a secondary vertex (SV) inside the jet. Systematic uncertainties have been reduced with respect to previous CMS W+c analyses, resulting in the most accurate measurements up to date. Measurements are performed at the particle (hadron) and parton levels, and are compared to predictions from Monte Carlo generators as well as theoretical calculations. Specifically, the measurements unfolded to the particle level are compared to the $\MADGRAPH$ Monte Carlo generator, that implements calculations up to next-to-leading order (NLO) in perturbative quantum chromodynamics (QCD) interfaced with parton showering simulations, whereas the measurements unfolded to the parton level are compared at fixed-order perturbative QCD calculations at the NLO and next-to-next-to-leading order (NNLO) accuracies. The theoretical predictions agree with the measurements within experimental and theoretical uncertainties. The measurements presented in this work will help increase the accuracy of the determination of the strange quark PDF of the proton. |
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Record creato 2025-01-03, modificato l'ultima volta il 2025-01-14
