A search for the rare decays B(s)(0)→μ+ μ- and B(0)→μ+ μ- is performed with 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 B(s)(0)→μ+ μ- candidates with respect to the background expectation. The probability that the background could produce such an excess or larger is 5.3×10(-4) corresponding to a signal significance of 3.5 standard deviations. A maximum-likelihood fit gives a branching fraction of B(B(s)(0)→μ+ μ-)=(3.2(-1.2)(+1.5))×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 B(0)→μ+ μ- candidates is consistent with the background expectation, giving an upper limit of B(B(0)→μ+ μ-)<9.4×10(-10) at 95% confidence level.

region at a hadron collider. This document discusses the implications of these first measurements on classes of extensions to the Standard Model, bearing in mind the interplay with the results of searches for on-shell production of new particles at ATLAS and CMS. The physics potential of an upgrade to the LHCb detector, which would allow an order of magnitude more data to be collected, is emphasised.

Abstract:The angular distribution and differential branching fraction of the decay B + → K + µ + µ − are studied with a dataset corresponding to 1.0 fb −1 of integrated luminosity, collected by the LHCb experiment. The angular distribution is measured in bins of dimuon invariant mass squared and found to be consistent with Standard Model expectations. Integrating the differential branching fraction over the full dimuon invariant mass range yields a total branching fraction of B(B + → K + µ + µ − ) = (4.36 ± 0.15 ± 0.18) × 10 −7 . These measurements are the most precise to date of the B + → K + µ + µ − decay.

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The properties of the orbitally excited (L ¼ 1) B 0 s states are studied by using 1:0 fb À1 of pp collisions at ffiffi ffi s p ¼ 7 TeV collected with the LHCb detector. The first observation of the B Ã s2 ð5840Þ 0 meson decaying to B Ãþ K À is reported, and the corresponding branching fraction measured relative to the B þ K À decay mode. The B s1 ð5830Þ 0 ! B Ãþ K À decay is observed as well. The width of the B Ã s2 ð5840Þ 0 state is measured for the first time, and the masses of the two states are determined with the highest precision to date. The observation of the B Ã s2 ð5840Þ 0 ! B Ãþ K À decay favors the spin-parity assignment J P ¼ 2 þ for the B Ã s2 ð5840Þ 0 meson. In addition, the most precise measurement of the mass difference mðB Ãþ Þ À mðB þ Þ ¼ 45:01 AE 0:30ðstatÞ AE 0:23ðsystÞ MeV=c 2 is obtained. DOI: 10.1103/PhysRevLett.110.151803 PACS numbers: 13.25.Hw, 12.39.Hg, 14.40.Nd Heavy quark effective theory describes mesons with one heavy and one light quark where the heavy quark is assumed to have infinite mass [1]. It is an important tool for calculating meson properties which may be modified by physics beyond the standard model, such as CP violation in charm meson decays [2] or the mixing and lifetimes of B mesons [3]. It also predicts the properties of excited B and B 0 s mesons [4][5][6][7], and precise measurements of these properties are a sensitive test of the validity of the theory. Within heavy quark effective theory the B 0 s mesons are characterized by three quantum numbers: the relative orbital angular momentum L of the two quarks, the total angular momentum of the light quark j q ¼ jL AE 1 2 j, and the total angular momentum of the B 0 s meson J ¼ jj q AE 1 2 j. For L ¼ 1 there are four different possible (J, j q ) combinations, all with even parity. These are collectively termed the orbitally excited states. Such states can decay to B þ K À and/or B Ãþ K À (the inclusion of charge-conjugate states is implied throughout this Letter), depending on their quantum numbers and mass values. The two states with j q ¼ 1=2, named B Ã s0 and B 0 s1 , are expected to decay through an S-wave transition and to have a large Oð100 MeV=c 2 Þ decay width. In contrast, the two states with j q ¼ 3=2, named B s1 ð5830Þ 0 and B Ã s2 ð5840Þ 0 (henceforth B s1 and B Ã s2 for brevity), are expected to decay through a D-wave transition and to have a narrow Oð1 MeV=c 2 Þ decay width. Table I gives an overview of these states.In this Letter, a 1:0 fb À1 sample of data collected by the LHCb detector is used to search for the orbitally excited B 0 s mesons in the mass distribution of B þ K À pairs, where the B þ mesons are selected in the four decay modes:Two narrow peaks were observed in the B þ K À mass distribution by the CDF Collaboration [9]. Putatively, they are identified with the states of the j q ¼ 3=2 doublet expected in heavy quark effective theory [4] and are named B s1 and B Ã s2 . As the B s1 ! B þ K À decay is forbidden, one of the mass peaks observed is interpreted as the B s1 ! B Ãþ K À decay fol...