Measurement of the production cross section for a W boson in association with a charm quark in proton–proton collisions at √s = 13 TeV

Abstract

The strange quark content of the proton is probed through the measurement of the production cross section for a W boson and a charm (c) quark in proton–proton collisions at a center-of-mass energy of 13

$$\,\text {Te}\hspace{-.08em}\text {V}$$

Te

V

. The analysis uses a data sample corresponding to a total integrated luminosity of 138

$$\,\text {fb}^{-1}$$

fb

- 1

collected with the CMS detector at the LHC. The W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm jets are tagged using the presence of a muon or a secondary vertex inside the jet. The

$$\hbox {W}+\hbox {c}$$

W + c

production cross section and the cross section ratio

$$R_\textrm{c}^{\pm }= \sigma ({\hbox {W}}^{+}+\bar{\text {c}})/\sigma (\hbox {W}^{-}+{\textrm{c}})$$

R c ±

= σ

(

W

+

+

c

¯

)

/ σ

(

W -

+ c )

are measured inclusively and differentially as functions of the transverse momentum and the pseudorapidity of the lepton originating from the W boson decay. The precision of the measurements is improved with respect to previous studies, reaching 1% in

$$R_\textrm{c}^{\pm }= 0.950 \pm 0.005\,\text {(stat)} \pm 0.010 \,\text {(syst)} $$

R c ±

= 0.950 ± 0.005

(stat) ± 0.010

(syst)

. The measurements are compared with theoretical predictions up to next-to-next-to-leading order in perturbative quantum chromodynamics.