Needham, Matthew DavidAl Saleh, Hussain Hassan A.2025-03-032024https://hdl.handle.net/20.500.14154/74956Using data from proton-proton collisions collected by the LHCb experiment at CERN during Run 2. This dissertation presents a measurement of the effective lifetime (τ_L) of the B_s meson in the B_s → J/ψη′ decay mode. The measured effective lifetime is τ_L = 1.416±0.033±0.010ps, With the first uncertainty being the statistical and the second is the systematic. These results are consistent with Standard Model predictions, within 1σ, and previous experimental measurements, further validating the SM framework. The dissertation suggests potential directions for future research, particularly in enhancing the precision of such measurements and investigating additional decay channels.38enParticle PhysicsThe Standard Model of Particle Physics (SM)B_s MesonLight LifetimeLHCb Run2Thesis