LHCb

Abstract:

A precision measurement of the $W$ -boson production cross section is performed using the $W\to \mu \nu$ decay channel, based on a sample of proton-proton collision data collected by the LHCb experiment at $\sqrt{s}=13\mathrm{TeV}$ and corresponding to an integrated luminosity of $5.1{\mathrm{fb}}^{-1}$ . The cross section is measured for muons with transverse momentum between 25 and 55 GeV and pseudorapidity between 2.0 and 4.5. The total production cross sections of $W$ bosons are measured to be ${\sigma }_{W^{+}\to {\mu }^{+}\nu }=1754.2\pm 1.5\pm 11.8\pm 35.1\mathrm{pb}$ ${\sigma }_{W^{-}\to {\mu }^{-}\overline{\nu }}=1178.1\pm 1.3\pm 9.7\pm 23.6\mathrm{pb}$ where uncertainties are statistical, systematic, and due to the luminosity determination, respectively. Differential distributions $\mathrm{d}{\sigma }_{W^{\pm }\to {\mu }^{\pm }\nu }/\mathrm{d}{\eta }^{{\mu }^{\pm }}$ are also presented. The total and differential cross sections are in good agreement with theoretical predictions at next-to-next-to-leading order in perturbative quantum chromodynamics. This measurement is significantly more precise than previous results in this kinematic regime.

Abstract:

The first measurement of the polarization of charm baryons by the LHCb experiment recorded in fixed-target mode is presented. The polarization of ${\mathrm{\Lambda }}_c$ baryons is studied in collisions of protons, at an energy of 2.51 TeV, incident on a gaseous target of neon, at a nucleon-nucleon center-of-mass energy of 68.6 GeV. The world’s first measurement of separate-charge polarizations for ${\mathrm{\Lambda }}_c^{+}$ and ${\overline{\mathrm{\Lambda }}}_c^{-}$ baryons is performed, determining $P_{{\mathrm{\Lambda }}_c^{+}}=(24\pm 9\pm 2)\%$ , $P_{{\overline{\mathrm{\Lambda }}}_c^{-}}=(-8\pm 12\pm 3)\%$ , where the first uncertainty is statistical and the second systematic. The polarization is also measured in intervals of baryon transverse momentum and the Feynman- $x$ variable.

Abstract:

A measurement of the flavor-untagged decay-time-integrated $CP$ asymmetry in the flavor-specific decay $B_s^0\to D_s^{-}{\pi }^{+}$ , $⟨A_{\text{untagged}}^s⟩$ , is performed using proton-proton collision data collected by the LHCb experiment between 2016 and 2018 at a center-of-mass energy of 13 TeV, corresponding to a total integrated luminosity of $5.4{\mathrm{fb}}^{-1}$ . The $CP$ asymmetry is measured in two $D_s^{-}$ meson decay modes, $D_s^{-}\to K^{-}{K}^{+}{\pi }^{-}$ and $D_s^{-}\to {\pi }^{-}{\pi }^{+}{\pi }^{-}$ . The combined result, $⟨A_{\text{untagged}}^s⟩=(-1.4\pm 5.9(\mathrm{stat})\pm 1.1(\mathrm{syst}))\times {10}^{-3}$ , is consistent with the Standard Model expectation and provides a direct constraint on new physics in tree-level $b$ -hadron decays.

Abstract:

This paper presents a thorough study of the local and nonlocal amplitudes in B+ → K+μ+μ− transitions through an amplitude analysis of the dimuon mass spectrum of the decay. The analysis is based on pp collision data corresponding to an integrated luminosity of 8.4 fb−1 collected by the LHCb experiment during Run1 and Run2. This measurement employs a model that describes both one-particle and two-particle nonlocal amplitudes across the entirety of the dimuon mass spectrum, enabling the determination of both short- and long-distance contributions to the decay. The compatibility of the Wilson coefficient combinations C9+C9′$$ {C}_9+{C}_9^{\prime } $$ and C10+C10′$$ {C}_{10}+{C}_{10}^{\prime } $$ with the Standard Model prediction is found to vary between 1.6 σ and 4 σ, depending on the choice of local form factors.