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Register a new userMeasurement of the $B^0_s to mu^+ mu^-$ branching fraction and search for $B^0 to mu^+ mu^-$ decays at the LHCb experiment
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A search for the rare decays $B^0_s tomu^+mu^-$ and $B^0 tomu^+mu^-$ is performed at the LHCb experiment. The data analysed correspond to an integrated luminosity of 1 fb$^{-1}$ of $pp$ collisions at a centre-of-mass energy of 7 TeV and 2 fb$^{-1}$ at 8 TeV. An excess of $B^0_s tomu^+mu^-$ signal candidates with respect to the background expectation is seen with a significance of 4.0 standard deviations. A time-integrated branching fraction of ${cal B}(B^0_s tomu^+mu^-) = (2.9^{+1.1}_{-1.0})times 10^{-9}$ is obtained and an upper limit of ${cal B}(B^0 tomu^+mu^-) < 7.4times 10^{-10}$ at 95% confidence level is set. These results are consistent with the Standard Model expectations.
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A search for the rare decays $B^0_stomu^+mu^-$ and $B^0tomu^+mu^-$ is performed at the LHCb experiment using data collected in $pp$ collisions corresponding to a total integrated luminosity of 4.4 fb$^{-1}$. An excess of $B^0_stomu^+mu^-$ decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be ${cal B}(B^0_stomu^+mu^-)=left(3.0pm 0.6^{+0.3}_{-0.2}right)times 10^{-9}$, where the first uncertainty is statistical and the second systematic. The first measurement of the $B^0_stomu^+mu^-$ effective lifetime, $tau(B^0_stomu^+mu^-)=2.04pm 0.44pm 0.05$ ps, is reported. No significant excess of $B^0tomu^+mu^-$ decays is found and a 95 % confidence level upper limit, ${cal B}(B^0tomu^+mu^-)<3.4times 10^{-10}$, is determined. All results are in agreement with the Standard Model expectations.
A search is performed for the lepton number violating decay $B^{+}to h^- mu^+ mu^+$, where $h^-$ represents a $K^-$ or a $pi^-$, using data from the LHCb detector corresponding to an integrated luminosity of $36pb^{-1}$. The decay is forbidden in the Standard Model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of $B(B^{+} to K^- mu^+ mu^+) < 5.4times 10^{-8}$ and $B(B^{+} to pi^- mu^+ mu^+) < 5.8times 10^{-8}$ are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.
A measurement of the differential branching fraction of the decay ${B^{0}rightarrow K^{ast}(892)^{0}mu^{+}mu^{-}}$ is presented together with a determination of the S-wave fraction of the $K^+pi^-$ system in the decay $B^{0}rightarrow K^{+}pi^{-}mu^{+}mu^{-}$. The analysis is based on $pp$-collision data corresponding to an integrated luminosity of 3,fb$^{-1}$ collected with the LHCb experiment. The measurements are made in bins of the invariant mass squared of the dimuon system, $q^2$. Precise theoretical predictions for the differential branching fraction of $B^{0}rightarrow K^{ast}(892)^{0}mu^{+}mu^{-}$ decays are available for the $q^2$ region $1.1<q^2<6.0,{rm GeV}^2/c^4$. In this $q^2$ region, for the $K^+pi^-$ invariant mass range $796 < m_{Kpi} < 996,{rm MeV}/c^2$, the S-wave fraction of the $K^+pi^-$ system in $B^{0}rightarrow K^{+}pi^{-}mu^{+}mu^{-}$ decays is found to be begin{equation*} F_{rm S} = 0.101pm0.017({rm stat})pm0.009 ({rm syst}), end{equation*} and the differential branching fraction of $B^{0}rightarrow K^{ast}(892)^{0}mu^{+}mu^{-}$ decays is determined to be begin{equation*} {rm d}mathcal{B}/{rm d} q^2 = (0.342_{,-0.017}^{,+0.017}({rm stat})pm{0.009}({rm syst})pm0.023({rm norm}))times 10^{-7}c^{4}/{rm GeV}^{2}. end{equation*} The differential branching fraction measurements presented are the most precise to date and are found to be in agreement with Standard Model predictions.
The angular distribution and differential branching fraction of the decay $B^{0} to K^{*0} mu^{+}mu^{-}$ are studied using a data sample, collected by the LHCb experiment in $pp$ collisions at $sqrt{s}=7,{rm TeV}$, corresponding to an integrated luminosity of $1.0,{rm fb}^{-1}$. Several angular observables are measured in bins of the dimuon invariant mass squared, $q^{2}$. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be $q_{0}^{2} = 4.9 pm 0.9 ,{rm GeV}^{2}/c^{4}$, where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions.
The branching fraction of the rare $B^0_srightarrowphimu^+mu^-$ decay is measured using data collected by the LHCb experiment at center-of-mass energies of $7$, $8$ and $13,rm{TeV}$, corresponding to an integrated luminosity of $9,{rm fb}^{-1}$. The branching fraction is reported in intervals of $q^2$, the square of the dimuon invariant mass. In the $q^2$ region between $1.1$ and $6.0,{rm Gekern -0.1em V}^2!/c^4$, the measurement is found to lie $3.6$ standard deviations below a Standard Model prediction based on a combination of Light Cone Sum Rule and Lattice QCD calculations. In addition, the first observation of the rare $B^0_srightarrow f_2^prime(1525)mu^+mu^-$ decay is reported with a statistical significance of nine standard deviations and its branching fraction is determined.
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