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Abstract:

The onset of nuclear effects in light-ion collisions is studied by measuring the ratio of $D^0$ meson production between NeNe and OO collisions at a center-of-mass energy per nucleon pair of 5.36 TeV recorded by the LHCb detector. The $D^0$ meson yields are measured differentially in transverse momentum ( $p_{\mathrm{T}}$ ) for $0.5<p_{\mathrm{T}}<20\mathrm{GeV}$ in the rapidity ( $y$ ) region $2.0<y<4.5$ , and are normalized to the total number of recorded inelastic nucleus-nucleus collisions in each data sample. The resulting production ratio shows evidence of variation as a function of $p_{\mathrm{T}}$ , which is inconsistent with predictions based on nuclear modification of nucleon structure alone. This measurement is consistent with the onset of quark-gluon plasma production with increasing nucleus size in high-energy nuclear collisions.

Abstract:

A search for $CP$ violation in the ${\stackrel{¯}{B}}^0→{\stackrel{¯}{K}}^{*0}{\mathrm{μ}}^{+}{\mathrm{μ}}^{−}$ decay is performed using proton-proton collision data collected by the LHCb experiment during Run 1 and Run 2, corresponding to an integrated luminosity of $8.4{\mathrm{fb}}^{−1}$ . The analysis exploits the full angular distribution of the decay, providing sensitivity to $CP$ -violating effects in both vector and axial-vector contributions to this flavor-changing neutral-current process. The complex Wilson coefficients are determined within the weak effective theory through an unbinned maximum-likelihood fit to the angular observables, incorporating nonlocal hadronic amplitudes across the full dimuon mass spectrum. The precision of the $CP$ -violation observables is improved by an order of magnitude relative to previous measurements, with the imaginary parts of the Wilson coefficients now determined more precisely than the real parts. No significant $CP$ violation is observed, and the results are consistent with the standard model.

Abstract:

The first search for the lepton-flavor violating decays $B^{+}→{\mathrm{Ï€}}^{+}{\mathrm{μ}}^{Â\pm }{e}^{∓}$ in proton-proton collisions is presented, using data collected by the LHCb experiment between 2011 and 2018, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{−1}$ . No significant signal is observed and an upper limit on the branching fraction is set at $\mathcal{B}(B^{+}→{\mathrm{Ï€}}^{+}{\mathrm{μ}}^{Â\pm }{e}^{∓})<1.8×{10}^{−9}$ at the 90% confidence level, 2 orders of magnitude more restrictive than the most stringent upper limit to date. This is the first constraint on lepton-flavor violating $b→d$ quark transitions at the LHC and also sets the most stringent upper limits to date on $b→d{\mathrm{μ}}^{Â\pm }{e}^{∓}$ transitions. Limits on left-handed and scalar scenarios beyond the standard model are also reported.

Abstract:

Measurements of the combined CP asymmetries in B¯0→Ds−D+$$ {\overline{B}}^0\to {D}_s^{-}{D}^{+} $$ and B¯s0→Ds−D−$$ {\overline{B}}_s^0\to {D}_s^{-}{D}^{-} $$ decays are made using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. The measurements are found to beACPB¯0→Ds−D+=0.0009±0.0053±0.0040,ACPB¯s0→Ds−D−=0.103±0.053±0.010,$$ {\displaystyle \begin{array}{l}{A}_{CP}\left({\overline{B}}^0\to {D}_s^{-}{D}^{+}\right)=0.0009\pm 0.0053\pm 0.0040,\\ {}{A}_{CP}\left({\overline{B}}_s^0\to {D}_s^{-}{D}^{-}\right)=0.103\pm 0.053\pm 0.010,\end{array}} $$where the first and second uncertainties are statistical and systematic, respectively. This is the first measurement of this asymmetry in B¯s0$$ {\overline{B}}_s^0 $$ decays, and the most precise measurement to date for B¯0$$ {\overline{B}}^0 $$ decays. Both measurements are found to be consistent with CP symmetry.