LHCb

Abstract:

The LHCb Ring-Imaging Cherenkov detectors are built to provide charged hadron identification over a large range of momentum. The upgraded detectors are also capable of providing an independent measurement of the luminosity for the LHCb experiment during LHC Run 3. The modelling of the opto-electronics chain, the application of the powering strategy during operations, the calibration procedures and the proof of principle of a novel technique for luminosity determination are presented. In addition, the preliminary precision achieved during the 2023 data-taking year for real-time and offline luminosity measurements is reported.

Abstract:

Using 20.3 fb–1 of annihilation data collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we report on an improved search for the radiative leptonic decay . An upper limit on its partial branching fraction for photon energies MeV was determined to be at a 90% confidence level; this excludes most current theoretical predictions. A sophisticated deep learning approach, which includes thorough validation and is based on the Transformer architecture, was implemented to efficiently distinguish the signal from massive backgrounds.

Abstract:

The first observation of the Ξb0 → J/ψΞ− π+ decay and the most precise measurement of the branching fraction of the Λb0 → J/ψΞ− K+ decay are reported, using proton-proton collision data from the LHCb experiment collected in 2016–2018 at a centre of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb−1. Using the Λb0 → J/ψΛ and Ξb0 → J/ψΞ− decays as normalisation channels, the ratios of branching fractions are measured to be B(Λb0 → J/ψΞ− K+)/B(Λb0 → J/ψΛ) = (1.17 ± 0.14 ± 0.08) × 10−2, B(Ξb0 → J/ψΞ− π+)/B(Ξb0 → J/ψΞ−) = (11.9 ± 1.4 ± 0.6) × 10−2, where the first uncertainty is statistical and the second systematic

Abstract:

The ratio of prompt production cross-sections of ψ(2S) and J/ψ mesons in their dimuon final state is measured as a function of centrality, using data collected by the LHCb detector in PbPb collisions at sNN = 5.02 TeV, for the first time in the forward rapidity region. The measured ratio shows no dependence on the collision centrality, and is compared to the latest theory predictions and to the recent measurements in literature.

Abstract:

A test of lepton universality between muons and electrons is performed using B+ → K+ℓ+ℓ− decays (where ℓ = e, μ), in the dilepton invariant-mass-squared region above 14.3 GeV2/c4. The data used for the measurement consists of beauty meson decays produced in proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1, collected by the LHCb experiment between 2011 and 2018. The ratio of branching fractions for B+→ K+μ+μ− and B+→ K+e+e− decays is measured to be RK=1.08−0.09+0.11stat−0.04+0.04syst, which is consistent with the Standard Model prediction of unity. This constitutes the most precise test of lepton flavour universality using B+ → K+ℓ+ℓ− decays with dilepton invariant-mass-squared above the ψ(2S) mass, whilst being the first of its kind at a hadron collider.