Measurement of the B0 s → μ+μ− branching fraction and search for B0 → μ+μ− with the CMS experiment

Chatrchyan, S. and Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Dragicevic, M. and Erö, J. and Fabjan, C. and Friedl, M. and Frühwirth, R. and Ghete, V. M. and Hörmann, N. and Hrubec, J. and Jeitler, M. and Kiesenhofer, W. and Knünz, V. and Krammer, M. and Krätschmer, I. and Liko, D. and Mikulec, I. and Rabady, D. and Rahbaran, B. and Rohringer, C. and Rohringer, H. and Schöfbeck, R. and Strauss, J. and Taurok, A. and Treberer-Treberspurg, W. and Waltenberger, W. and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Molnár, József and Pálinkás, József and Karancsi, János and Trócsányi, Zoltán and Ujvári, Balázs and Krajczár, Krisztián and Veres, Gábor (2013) Measurement of the B0 s → μ+μ− branching fraction and search for B0 → μ+μ− with the CMS experiment. PHYSICAL REVIEW LETTERS, 111 (10). ISSN 0031-9007

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Abstract

Results are presented from a search for the rare decays B0 s → μ+μ− and B0 → μ+μ− in pp collisions at √s = 7 and 8 TeV, with data samples corresponding to integrated luminosities of 5 and 20 fb−1, respectively, collected by the CMS experiment at the LHC. An unbinned maximum-likelihood fit to the dimuon invariant mass distribu- tion gives a branching fraction B(B0 s → μ+μ−) = (3.0+1.0 −0.9) × 10−9, where the uncer- tainty includes both statistical and systematic contributions. An excess of B0 s → μ+μ− events with respect to background is observed with a significance of 4.3 standard de- viations. For the decay B0 → μ+μ− an upper limit of B(B0 → μ+μ−) < 1.1 × 10−9 at the 95% confidence level is determined. Both results are in agreement with the expectations from the standard model.

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