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Abstract:

The first measurements of the top- and antitop-quark differential production cross sections and the top-quark charge asymmetry in the forward region are presented, using proton-proton collision data collected by the LHCb experiment at a center-of-mass energy of 13 TeV corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{−1}$ . The total production cross sections of top and antitop quarks are also determined. Measurements are performed using the $\mathrm{μ}+b\text{-jet}$ final state within a fiducial region defined by $b$ -jet $p_{\mathrm{T},\text{jet}}>50\mathrm{GeV}$ and pseudorapidity $2.2<{\mathrm{η}}_{\text{jet}}<4.0$ , with the muon from the $W$ -boson decay required to have $p_{\mathrm{T},\mathrm{μ}}>25\mathrm{GeV}$ and $2.0<{\mathrm{η}}_{\mathrm{μ}}<4.5$ . The muon and $b$ -jet system must satisfy $p_{\mathrm{T}}(\mathrm{μ}+\text{jet})>20\mathrm{GeV}$ . The measured integrated production cross sections for the top and antitop quarks are ${\mathrm{σ}}_t=0.95Â\pm 0.04Â\pm 0.08Â\pm 0.02\mathrm{pb}$ , ${\mathrm{σ}}_{\stackrel{¯}{t}}=0.81Â\pm 0.03Â\pm 0.07Â\pm 0.02\mathrm{pb}$ , where the first uncertainty is statistical, the second systematic, and the third accounts for the luminosity uncertainty. The top-quark charge asymmetry is measured to be $A_C^t=0.08Â\pm 0.03Â\pm 0.01$ , where the first uncertainty is statistical and the second is systematic. These results are consistent with next-to-leading order Standard Model predictions.

Abstract:

The collinear and transverse-momentum-dependent jet fragmentation function and the radial profile for $B^{Â\pm }$ mesons in jets are measured. The $B^{Â\pm }$ mesons are reconstructed through the $J/\mathrm{ψ}(→{\mathrm{μ}}^{+}{\mathrm{μ}}^{−})K^{Â\pm }$ decay channel using proton-proton collision data collected during 2016–2018 with the LHCb detector at a center-of-mass (c.m.) energy of $\sqrt{s}=13\mathrm{TeV}$ , corresponding to an integrated luminosity of $5.4{\mathrm{fb}}^{−1}$ . The results complement recent measurements of jet fragmentation functions for heavy-flavor hadrons and suggest a growing contribution of gluon fragmentation to $B^{Â\pm }$ mesons as the jet transverse momentum increases.

Abstract:

A search for $CP$ violation with an entangled system of ${\mathrm{Ó\copyright }}^{−}{\stackrel{¯}{\mathrm{Ó\copyright }}}^{+}$ pairs is performed, using $(10,087Â\pm 44)×{10}^{6}J/\mathrm{ψ}$ events collected with the BESIII experiment. A nine-dimensional helicity amplitude is used to fit $e^{+}{e}^{−}→J/\mathrm{ψ}→{\mathrm{Ó\copyright }}^{−}{\stackrel{¯}{\mathrm{Ó\copyright }}}^{+}$ and its subsequent decays. The ${\mathrm{Ó\copyright }}^{−}$ and ${\stackrel{¯}{\mathrm{Ó\copyright }}}^{+}$ decay parameters are determined with higher precision compared to the best results reported so far. Furthermore, the strong phase difference, $({\mathrm{δ}}_P−{\mathrm{δ}}_S)=(0.3Â\pm 1.2Â\pm 0.2)×{10}^{−2}\mathrm{rad}$ , and the weak phase difference, $({\mathrm{ξ}}_P−{\mathrm{ξ}}_S)=(−0.2Â\pm 1.2Â\pm 0.1)×{10}^{−2}\mathrm{rad}$ , are directly determined. These are the most precise measurements to date. The $CP$ asymmetry observables $A_{CP}^{\mathrm{Ó\copyright }}=(−7.8Â\pm 4.8Â\pm 0.8)×{10}^{−3}$ and $\mathrm{Δ}{\mathrm{Ï•}}_{CP}^{\mathrm{Ó\copyright }}=(0.6Â\pm 5.1Â\pm 0.2)×{10}^{−3}\mathrm{rad}$ are determined, which are consistent with $CP$ conservation. In addition, independent measurements of the $\mathrm{Âì}$ decay parameter and $CP$ asymmetry $A_{CP}^{\mathrm{Âì}}=(−2.9Â\pm 4.3Â\pm 0.7)×{10}^{−3}$ are also obtained, which are in agreement with the previous measurements, but with much improved precision.