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Measurement of the effective $B_s^0 \to K^+ K^-$ lifetime

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Abstract

A precise determination of the effective $B_s^0 \rightarrow K^+ K^-$ lifetime can be used to constrain contributions from physics beyond the Standard Model in the $B_s^0$ meson system. Conventional approaches select $B$ meson decay products that are significantly displaced from the $B$ meson production vertex. As a consequence, $B$ mesons with low decay times are suppressed, introducing a bias to the decay time spectrum which must be corrected. This analysis uses a technique that explicitly avoids a lifetime bias by using a neural network based trigger and event selection. Using 1.0 fb$^{-1}$ of data recorded by the LHCb experiment, the effective $B_s^0 \rightarrow K^+ K^-$ lifetime is measured as $1.455 \pm 0.046 \; \mathrm{(stat.)} \pm 0.006 \; \mathrm{(syst.)} \, \mathrm{ps}.$

Figures and captions

(a) Invariant mass spectrum for all selected $ B ^0_ s \!\rightarrow K ^+ K ^- $ candidates. (b) Decay time distribution of $ B ^0_ s \!\rightarrow K ^+ K ^- $ signal extracted using sWeights and the fitted exponential function.

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Combined efficiency of LHCb trigger, selection neural networks and particle identification requirements as a function of decay time for simulated $ B ^0_ s \!\rightarrow K ^+ K ^- $ signal candidates.

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Animated gif made out of all figures.

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Tables and captions

Contributions to the systematic uncertainty on the effective $ B ^0_ s \!\rightarrow K ^+ K ^- $ lifetime measurement. The total uncertainty is calculated by adding the individual contributions in quadrature.

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Created on 09 December 2018.Citation count from INSPIRE on 18 December 2018.