Sneha Malde

Abstract:

A search for rare B → Dμ+μ− decays is performed using proton-proton collision data collected by the LHCb experiment, corresponding to an integrated luminosity of 9 fb−1. No significant signals are observed in the non-resonant μ+μ− modes, and upper limits of BB0→D¯0μ+μ−<5.1×10−8, BB+→Ds+μ+μ−<3.2×10−8, BBs0→D¯0μ+μ−<1.6×10−7 and fc/fu·BBc+→Ds+μ+μ−<9.6×10−8 are set at the 95 % confidence level, where fc and fu are the fragmentation fractions of a B meson with a c and u quark respectively in proton-proton collisions. Each result is either the first such measurement or an improvement by three orders of magnitude on an existing limit. Separate upper limits are calculated when the muon pair originates from a J/ψ → μ+μ− decay. The branching fraction of Bc+→Ds+J/ψ multiplied by the fragmentation-fraction ratio is measured to befcfu·BBc+→Ds+J/ψ=1.63±0.15±0.13×10−5, where the first uncertainty is statistical and the second systematic.

Abstract:

The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using pp collision data at √(s) = 13 TeV recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of 5.5 fb-1. A total of around 105 helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately 50% with a corresponding background rejection rate of up to Script O(1012). These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei