A new algorithm for identifying the flavour of B0 s mesons at LHCb

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  • LHCb Collaboration

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  • CERN
  • Universität Zörich
  • Universidad de Santiago de Compostela
  • University of Bristol
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  • TU Dortmund University, Germany
  • University of Glasgow
  • Institution Nikhef National Institute for Subatomic Physics
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  • Institute for High Energy Physics (IHEP)
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  • University of Warwick
  • Universitat de Barcelona
  • Pontifícia Universidade Católica Do Rio de Janeiro


A new algorithm for the determination of the initial flavour of B0 s 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 B0 s meson. The second network combines the kaon charges to assign the B0 s 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 protonproton collisions at 7 and 8 TeV centre-of-mass energies. The calibration is performed in two ways: by resolving the B0 sB0 s flavour oscillations in B0 s →D- s φ+ decays, and by analysing flavour-specific B∗ s2 (5840)0→ B+K- decays. The tagging power measured in B0 s → D- s φ+ decays is found to be (1:80 ± 0:19 (stat) ± 0:18 (syst))%, which is an improvement of about 50% compared to a similar algorithm previously used in the LHCb experiment.


Original languageEnglish
Article numberP05010
JournalJournal of Instrumentation
Issue number5
Publication statusPublished - 17 May 2016


  • Analysis and statistical methods, Calibration and fitting methods, Cluster finding, Particle identification methods, Pattern recognition

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