Measurement of the effective $B^0_s \rightarrow K^+ K^-$ lifetime

A precise determination of the effective $B^0_s \rightarrow K^+ K^-$ lifetime can be used to put constraints on new physics contributions in the $B_s^0$ meson system. Conventional approaches to select $B$ mesons and suppress combinatorial background rely on decay products which are significantly displaced from the primary vertex in which the $B$ meson has been produced. As a consequence, $B$ mesons at low lifetimes are suppressed and the spectrum of the measured decay time is biased. This analysis presents a novel technique which avoids such a bias using a neural network approach in a dedicated trigger and event selection. Using 1.0 fb$^{-1}$ of data recorded by the LHCb experiment in 2011, the effective $B^0_s \rightarrow K^+ K^-$ lifetime is measured as $\tau_{KK} = 1.468 \pm 0.046 \; \mathrm{(stat.)} \pm 0.006 \; \mathrm{(syst.)} \, \mathrm{ps}.$