A new algorithm for identifying the flavour of $B_s^0$ mesons at LHCb

Abstract

A new algorithm for the determination of the initial flavour of $B_s^0$ mesons is presented. The algorithm is based on two neural networks and exploits the $b$ hadron production mechanism at a hadron collider. The first network is trained to select charged kaons produced in association with the $B_s^0$ meson. The second network combines the kaon charges to assign the $B_s^0$ flavour and estimates the probability of a wrong assignment. The algorithm is calibrated using data corresponding to an integrated luminosity of 3 fb${}^{-1}$ collected by the LHCb experiment in proton-proton collisions at 7 and 8 TeV centre-of-mass energies. The calibration is performed in two ways: by resolving the $B_s^0$-${\bar{B}}_s^0$ flavour oscillations in $B_s^0\to D_s^{-}{\pi }^{+}$ decays, and by analysing flavour-specific $B_{s2}^{\ast }(5840{)}^0\to B^{+}{K}^{-}$ decays. The tagging power measured in $B_s^0\to D_s^{-}{\pi }^{+}$ decays is found to be $(1.80\pm 0.19(\mathrm{stat})\pm 0.18(\mathrm{syst}))$\%, which is an improvement of about 50\% compared to a similar algorithm previously used in the LHCb experiment.

All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2015-056.html

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• PYTHIA 6.4 Physics and Manual
• Big-Bang Nucleosynthesis
• Measurement of the CP-violating phase ${\varphi }_s$ in ${\overline{B}}_s^0\to J/\psi {\pi }^{+}{\pi }^{-}$ decays
• Opposite-side flavour tagging of B mesons at the LHCb experiment
• $B$ flavour tagging using charm decays at the LHCb experiment
• Measurement of CP violation in $B_s^0\to \varphi \varphi$ decays
• Determination of the branching fractions of $B_s^0\to D_s^{\mp }{K}^{\pm }$ and $B^0\to D_s^{-}{K}^{+}$

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• The CKM Parameters
• Measurement of the $CP$ asymmetry in $B_s^0-\overline{B}{}_s^0$ mixing
• Measurement of $CP$ asymmetries in two-body $B_{(s)}^0$-meson decays to charged pions and kaons
• Resonances and $CP$ violation in $B_s^0$ and ${\overline{B}}_s^0\to J/\psi K^{+}{K}^{-}$ decays in the mass region above the $\varphi (1020)$
• CP violation in the B system
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• First measurement of the $CP$-violating phase ${\varphi }_s^{d\overline{d}}$ in $B_s^0\to (K^{+}{\pi }^{-})(K^{-}{\pi }^{+})$ decays
• Measurement of CP violation in the $B_s^0\to \varphi \varphi$ decay and search for the $B^0\to \varphi \varphi$ decay
• Improved measurement of $CP$ violation parameters in $B_s^0\to J/\psi K^{+}{K}^{-}$ decays in the vicinity of the $\varphi (1020)$ resonance
• Predictions of Angular Observables for ${\bar{B}}_s\to K^{\ast }\ell \ell$ and $\bar{B}\to \rho \ell \ell$ in Standard Model
• Studying the potential of Graphcore IPUs for applications in Particle Physics
• Precision measurement of $CP$ violation in the penguin-mediated decay $B_s^0\to \varphi \varphi$
• Inclusive Flavour Tagging Algorithm
• First measurement of the $CP$-violating phase in $B_s^0\to J/\psi (\to e^{+}{e}^{-})\varphi$ decays