Search for the Lepton-Flavor-Violating Decays Bs0 →τ±μâ" and B0 →τ±μâ"

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  • LHCb Collaboration

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  • Nikhef National Institute for Subatomic Physics
  • University of Zurich
  • Universidad de Santiago de Compostela
  • University of Bristol
  • University of Michigan
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  • University of Cincinnati
  • Laboratori Nazionali dell'Infn di Frascati
  • TU Dortmund University, Germany
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  • University of Glasgow
  • Universitat de Barcelona
  • Petersburg Nuclear Physics Institute (PNPI)
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  • Syracuse University
  • Yandex School of Data Analysis
  • INFN Sezione di Cagliari
  • Ruprecht-Karls-Universität Heidelberg
  • University of Warwick
  • Institute of Physics


Results are reported from a search for the rare decays Bs0→τ±μâ" and B0→τ±μâ", where the τ lepton is reconstructed in the channel τ-→π-π+π-ντ. These processes are effectively forbidden in the standard model, but they can potentially occur at detectable rates in models of new physics that can induce lepton-flavor-violating decays. The search is based on a data sample corresponding to 3 fb-1 of proton-proton collisions recorded by the LHCb experiment in 2011 and 2012. The event yields observed in the signal regions for both processes are consistent with the expected standard model backgrounds. Because of the limited mass resolution arising from the undetected τ neutrino, the Bs0 and B0 signal regions are highly overlapping. Assuming no contribution from B0→τ±μâ", the upper limit B(Bs0→τ±μâ")<4.2×10-5 is obtained at 95% confidence level. If no contribution from Bs0→τ±μâ" is assumed, a limit of B(B0→τ±μâ")<1.4×10-5 is obtained at 95% confidence level. These results represent the first limit on B(Bs0→τ±μâ") and the most stringent limit on B(B0→τ±μâ").


Original languageEnglish
Article number211801
JournalPhysical Review Letters
Issue number21
Publication statusPublished - 22 Nov 2019

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