M. Hoballah

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

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.

Measurement of

A bstract The production of J/ψ mesons is studied with the LHCb detector using data from pp collisions at

J/\psi

\sqrt{s}=2.76

production in

TeV corresponding to an integrated luminosity of 71 nb−1. The differential cross-section for inclusive J/ψ production is measured as a function of its transverse momentum pT. The cross-section in the fiducial region 0 < pT  < 12 GeV/c and rapidity 2.0 <

pp

y

collisions at

< 4.5 is measured to be 5.6 ± 0.1 (stat) ± 0.4 (syst) μb, with the assumption of unpolarised J/ψ production. The fraction of J/ψ production from b-hadron decays is measured to be (7.1 ± 0.6 (stat) ± 0.7 (syst))%.

\sqrt{s}=2.76

A search for the decay K0S→μ+μ− is performed, based on a data sample of 1.0 fb−1 of pp collisions at √ s =7 TeV collected by the LHCb experiment at the Large Hadron Collider. The observed number of candidates is consistent with the background-only hypothesis, yielding an upper limit of B(K0S→μ+μ−) < 11(9) × 10−9 at 95 (90)% confidence level. This limit is a factor of thirty below the previous measurement.A bstractA search for the decay

TeV

K_{\mathrm{S}}^0\to {\mu^{+}}{\mu^{-}}

Search for the rare decay K^0_S -> mu+ mu-

is performed, based on a data sample of 1.0 fb−1 of pp collisions at

Measurement of

\sqrt{s}=7\;\mathrm{TeV}