Malcolm John

Abstract:

A method is presented to reconstruct charged particles with lifetimes between 10ps and 10ns, which considers a combination of their decay products and the partial tracks created by the initial charged particle. Using the Ξ- baryon as a benchmark, the method is demonstrated with simulated events and proton-proton collision data at s=13TeV, corresponding to an integrated luminosity of 2.0fb-1 collected with the LHCb detector in 2018. Significant improvements in the angular resolution and the signal purity are obtained. The method is implemented as part of the LHCb Run 3 event trigger in a set of requirements to select detached hyperons. This is the first demonstration of the applicability of this approach at the LHC, and the first to show its scaling with instantaneous luminosity.

Abstract:

The Λb0 → D+D−Λ decay is observed for the first time 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 5.3 fb−1. Using the B0 → D+D−KS0 decay as a reference channel, the product of the relative production cross-section and decay branching fractions is measured to beR=σΛb0σB0=BΛb0→D+D−ΛBB0→D+D−KS0=0.179±0.022±0.014, where the first uncertainty is statistical and the second is systematic. The known branching fraction of the reference channel, BB0→D+D−KS0, and the cross-section ratio, σΛb0/σB0, previously measured by LHCb are used to derive the branching fraction of the Λb0→ D+D−Λ decayBΛb0→D+D−Λ=1.24±0.15±0.10±0.28±0.11×10−4, where the third and fourth contributions are due to uncertainties of BB0→D+D−KS0 and σΛb0/σB0, respectively. Inspection of the D+Λ and D+D− invariant-mass distributions suggests a rich presence of intermediate resonances in the decay. The Λb0 → D*+D−Λ decay is also observed for the first time as a partially reconstructed component in the D+D−Λ invariant mass spectrum.

Abstract:

A search for the fully reconstructed Bs0→ μ+μ−γ decay is performed at the LHCb experiment using proton-proton collisions at s = 13 TeV corresponding to an integrated luminosity of 5.4 fb−1. No significant signal is found and upper limits on the branching fraction in intervals of the dimuon mass are setBBs0→μ+μ−γ<4.2×10−8, mμ+μ−∈2mμ1.70GeV/c2, BBs0→μ+μ−γ<7.7×10−8, mμ+μ−∈1.70, 2.88GeV/c2, BBs0→μ+μ−γ<4.2×10−8, mμ+μ−∈3.92mBs0GeV/c2, at 95% confidence level. Additionally, upper limits are set on the branching fraction in the [2mμ, 1.70] GeV/c2 dimuon mass region excluding the contribution from the intermediate ϕ(1020) meson, and in the region combining all dimuon-mass intervals.

Abstract:

The resonant structure of the radiative decay Λb0→pK−γ in the region of proton-kaon invariant-mass up to 2.5 GeV/c2 is studied using proton-proton collision data recorded at centre-of-mass energies of 7, 8, and 13 TeV collected with the LHCb detector, corresponding to a total integrated luminosity of 9 fb−1. Results are given in terms of fit and interference fractions between the different components contributing to this final state. Only Λ resonances decaying to pK− are found to be relevant, where the largest contributions stem from the Λ(1520), Λ(1600), Λ(1800), and Λ(1890) states.