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Abstract:

Muon-electron universality is tested in $B^0→K^{*0}{â„“}^{+}{â„“}^{−}$ decays, in the dilepton-invariant-mass region above the $\mathrm{ψ}(2S)$ resonance. The analysis uses beauty mesons produced in proton-proton collisions recorded by the LHCb detector at center-of-mass energies of 7, 8, and 13 TeV, corresponding to an integrated luminosity of $9{\mathrm{fb}}^{−1}$ . The ratio of branching fractions between the muon and electron channels $R_{K^{*0}}$ is measured to be ${1.08}_{−0.12}^{+0.14}(\mathrm{stat})Â\pm 0.07(\mathrm{syst})$ for a dilepton-invariant-mass squared above $14.0{\mathrm{GeV}}^2/c^4$ , consistent with the standard model prediction. This result represents the most precise measurement of $R_{K^{*0}}$ in this region and the first such measurement performed at a hadron collider.

Abstract:

Two machine learning techniques for jet measurements at the LHCb experiment are presented: a regression-based method for jet-energy calibration and a deep neural network algorithm for jet flavour tagging, distinguishing between b-quark, c-quark, and light parton jets. These techniques are applied to a search for inclusive H→bb¯$$ H\to b\overline{b} $$ and H→cc¯$$ H\to c\overline{c} $$ decays using a LHCb dataset corresponding to an integrated luminosity of 1.6 fb−1. The observed (expected) 95% confidence level upper limits correspond to 6.6 (11.1) times the SM cross-section for the H→bb¯$$ H\to b\overline{b} $$ process, and 1003 (1834) times the SM cross-section for the H→cc¯$$ H\to c\overline{c} $$ process.

Abstract:

The time-dependent $CP$ asymmetry in $B^0→J/\mathrm{ψ}\mathrm{ÒÏ}(770{)}^0$ decays is measured using proton-proton collision data corresponding to an integrated luminosity of $6{\mathrm{fb}}^{−1}$ , collected with the LHCb detector at a center-of-mass energy of 13 TeV during the years 2015–2018. The $CP$ -violation parameters for this process are determined to be $2{\mathrm{β}}_{c\stackrel{¯}{c}d}^{\mathrm{eff}}=0.710Â\pm 0.084Â\pm 0.051\mathrm{rad}$ and $|\mathrm{λ}|=1.019Â\pm 0.034Â\pm 0.024$ , where the first uncertainty is statistical and the second systematic. This constitutes the first observation of time-dependent $CP$ violation in $B^0→J/\mathrm{ψ}\mathrm{ÒÏ}(770{)}^0$ decays. Assuming approximate SU(3) flavor symmetry, these results are combined with the previous consistent LHCb measurement to set the most stringent constraint on the penguin contribution, $\mathrm{Δ}{\mathrm{Ï•}}_s$ , to the $CP$ -violating phase ${\mathrm{Ï•}}_s$ in $B_s^0→J/\mathrm{ψ}\mathrm{Ï•}(1020)$ decays, yielding $\mathrm{Δ}{\mathrm{Ï•}}_s=5.0Â\pm 4.6\mathrm{mrad}$ .

Abstract:

An analysis of the $B^0→K^{*0}(→K^{+}{\mathrm{π}}^{−}){\mathrm{μ}}^{+}{\mathrm{μ}}^{−}$ decay is presented using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of $8.4{\mathrm{fb}}^{−1}$ . The full set of $CP$ -averaged and $CP$ -asymmetric angular observables is determined in bins of the invariant mass squared of the dimuon system, as well as the branching fraction relative to the $B^0→J/\mathrm{ψ}(→{\mathrm{μ}}^{+}{\mathrm{μ}}^{−})K^{+}{\mathrm{π}}^{−}$ decay. For the first time, the full set of observables pertaining to the $K^{+}{\mathrm{π}}^{−}$ S-wave contribution to the final state are presented and consideration is given to effects arising from the mass of the muons. The extracted $CP$ -asymmetry observables show no significant deviations from zero. The measurements of the $CP$ -averaged observables and the branching fractions continue to exhibit the pattern of tensions with the standard model predictions that have been seen in previous analyses that use part of the dataset considered in this Letter.

Abstract:

The first observation of the doubly charmed baryon ${\mathrm{Ó\copyright }}_{cc}^{+}$ is reported through its decay to the ${\mathrm{Âì}}_c^{+}{K}^{−}{\mathrm{Ï€}}^{+}$ final state, with a statistical significance exceeding seven standard deviations. The observation is made using proton-proton collision data collected in 2024 with the LHCb Run 3 detector at a center-of-mass energy of 13.6 TeV, corresponding to a total integrated luminosity of $6.9{\mathrm{fb}}^{−1}$ . The ${\mathrm{Ó\copyright }}_{cc}^{+}$ mass is measured to be $3619.97Â\pm 0.83Â\pm {0.26}_{−1.30}^{+1.90}\mathrm{MeV}/c^2$ , where the first uncertainty is statistical, the second is systematic, and the third is due to the unknown ${\mathrm{Ó\copyright }}_{cc}^{+}$ lifetime, which is assumed to lie in the range 15–160 fs with a baseline value of 45 fs. The difference between the masses of the ${\mathrm{Ó\copyright }}_{cc}^{+}$ and ${\mathrm{Ó\copyright }}_{cc}^{++}$ baryons is determined to be $−1.77Â\pm 0.84Â\pm {0.15}_{−1.30}^{+1.90}\mathrm{MeV}/c^2$ . This is the first observation of a new particle made with the LHCb Run 3 detector.