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First evidence for the decay Bs -> mu+ mu-

Abstract : A search for the rare decays Bs->mu+mu- and B0->mu+mu- is performed using data collected in 2011 and 2012 with the LHCb experiment at the Large Hadron Collider. The data samples comprise 1.1 fb^-1 of proton-proton collisions at sqrt{s} = 8 TeV and 1.0 fb^-1 at sqrt{s}=7 TeV. We observe an excess of Bs -> mu+ mu- candidates with respect to the background expectation. The probability that the background could produce such an excess or larger is 5.3 x 10^-4 corresponding to a signal significance of 3.5 standard deviations. A maximum-likelihood fit gives a branching fraction of BR(Bs -> mu+ mu-) = (3.2^{+1.5}_{-1.2}) x 10^-9, where the statistical uncertainty is 95% of the total uncertainty. This result is in agreement with the Standard Model expectation. The observed number of B0 -> mu+ mu- candidates is consistent with the background expectation, giving an upper limit of BR(B0 -> mu+ mu-) < 9.4 x 10^-10 at 95% confidence level.
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Contributor : Sabine Starita <>
Submitted on : Tuesday, November 13, 2012 - 10:19:42 AM
Last modification on : Thursday, February 25, 2021 - 10:58:21 AM

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R. Aaij, S. Barsuk, O. Callot, J. He, B. Jean-Marie, et al.. First evidence for the decay Bs -> mu+ mu-. Physical Review Letters, American Physical Society, 2013, 110, pp.021801. ⟨10.1103/PhysRevLett.110.021801⟩. ⟨in2p3-00751272⟩



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