Measurement of $\Delta \Gamma_s$ using the $B^0_s$ decays to the final states $J/\psi \eta^{\prime}$ and $J/\psi f_0$}

Abstract

The main research field of the Large Hadron Collider beauty (LHCb) experiment at Large Hadron Collider (LHC) is the study of CP violation and rare decays of beauty and charm hadrons. Measurement of the B⁰ₛ mixing parameters ΔΓₛ, Γₛ, Δmₛ and ϕₛ provide a precise test of the Standard Model (SM). New particles, as predicted in models of physics beyond the SM may alter the measured values of B⁰ₛ mixing parameters compared to the SM. In this thesis, a measurement of ΔΓₛ is made by comparing the lifetimes in the B⁰ₛ → J/ψη′ and B⁰ₛ → J/ψf₀ decay modes.

This work uses the full data set recorded by the LHCb detector between 2011 and 2018. The value of ΔΓₛ is determined by measuring the yields of the two channels in bins of decay time, computing the ratio between the two channels in each bin and performing a χ² minimization. This technique, combined with the choice of two decay channels with similar topology, reduces the impact of the time acceptance introduced by the detector.

The measured value of ΔΓₛ is ΔΓₛ = (0.081 ± 0.011 ± 0.009) ps⁻¹ where the first uncertainty is statistical and the second is systematic.

At the end of 2018 the LHC started a major upgrade to deliver better performance. During this period, most of the LHCb sub-detectors were upgraded as well as the data acquisition system. After the upgrade, the new software infrastructure will need to be more robust and scalable to face the higher luminosity delivered by the LHC. With this new configuration, monitoring the status of the detector and the data collected will be crucial to assure the best performance of the detector. For this reason, a prototype for the High Level Trigger (HLT) monitoring system was designed, implemented and tested. The goal of this system was to check the feasibility of having a monitoring system running on off-the-shelf software instead of developing everything from scratch.