Measurement of the production of a $W$ boson in association with a charmed hadron in $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$ with the ATLAS detector

Abstract

The production of a $W$ boson in association with a single charm quark is studied using 140 ${\mathrm{fb}}^{-1}$ of $\sqrt{s}=13\mathrm{TeV}$ proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. The charm quark is tagged by a charmed hadron, reconstructed with a secondary-vertex fit. The $W$ boson is reconstructed from an electron/muon decay and the missing transverse momentum. The mesons reconstructed are $D^{\pm }\to K^{\mp }{\pi }^{\pm }{\pi }^{\pm }$ and $D^{\ast \pm }\to D^0{\pi }^{\pm }\to (K^{\mp }{\pi }^{\pm }){\pi }^{\pm }$, where $p_{\text{T}}(e,\mu )>30\mathrm{GeV}$, $|\eta (e,\mu )|<2.5$, $p_{\text{T}}(D)>8\mathrm{GeV}$, and $|\eta (D)|<2.2$. The integrated and normalized differential cross-sections as a function of the pseudorapidity of the lepton from the $W$ boson decay, and of the transverse momentum of the meson, are extracted from the data using a profile likelihood fit. The measured fiducial cross-sections are ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}-\mathrm{SS}}(W^{-}+D^{+})=50.2\pm 0.2(stat.){}_{-2.3}^{+2.4}(syst.)\mathrm{pb}$, ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}-\mathrm{SS}}(W^{+}+D^{-})=48.5\pm 0.2(stat.){}_{-2.2}^{+2.3}(syst.)\mathrm{pb}$, ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}-\mathrm{SS}}(W^{-}+D^{\ast +})=51.1\pm 0.4(stat.){}_{-1.8}^{+1.9}(syst.)\mathrm{pb}$, and ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}-\mathrm{SS}}(W^{+}+D^{\ast -})=50.0\pm 0.4(stat.){}_{-1.8}^{+1.9}(syst.)\mathrm{pb}$. Results are compared with the predictions of next-to-leading-order quantum chromodynamics calculations performed using state-of-the-art parton distribution functions. The ratio of charm to anti-charm production cross-sections is studied to probe the $s$-$\bar{s}$ quark asymmetry and is found to be $R_c^{\pm }=0.971\pm 0.006(stat.)\pm 0.011(syst.)$.

78 pages in total, author list starting page 61, 13 figures, 21 tables, published by Phys. Rev. D. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2019-22

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