Measurement of the W boson decay branching fraction ratio $\mathcal{B}$(W $\to$ cq) / $\mathcal{B}$(W $\to$ $\mathrm{q\bar{q}'}$) in proton-proton collisions at $\sqrt{s}$ = 13 TeV

TL;DR

This paper reports the most precise measurement to date of the W boson decay branching ratio into charm quarks relative to all hadronic decays, using proton-proton collision data at 13 TeV from the CMS experiment.

Contribution

It provides the first high-precision measurement of the W boson decay ratio into charm quarks at the LHC, improving the accuracy over previous results.

Findings

Measured $R_c^W$ = 0.489 ± 0.020, consistent with the Standard Model.

Achieved twice the precision of the current world-average value.

Utilized charm jet tagging via muons inside jets in a large CMS dataset.

Abstract

The most precise measurement to date of the W boson hadronic decay branching fraction ratio $R_\mathrm{c}^\mathrm{W}$ = $\mathcal{B}$(W $\to$ cq) / $\mathcal{B}$(W $\to$ $\mathrm{q\bar{q}'}$) is presented. The measurement is based on a sample of proton-proton collision data from the CERN LHC collected by the CMS experiment at a center-of-mass energy of 13 TeV in 2016-2018 with an integrated luminosity of 138 fb$^{-1}$. The large cross section of top quark-antiquark production at the LHC offers a sizable high-purity sample of W bosons suitable for this measurement. Events with one charged lepton (electron or muon) and at least four jets, two tagged as bottom quark jets, are analyzed. Charm jets are tagged using the presence of a muon inside the jet. The result, $R_\mathrm{c}^\mathrm{W}$ = 0.489 $\pm$ 0.020, is consistent with the standard model prediction and is twice as precise as the current world-average value.