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Register a new userObservation of the Decay K+ --> pi+ mu+ mu-
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We have observed the rare decay K+ --> pi+ mu+ mu- and measured the branching ratio Gamma(K+ --> pi+ mu+ mu-)/Gamma(K+ --> all) = (5.0 +/- 0.4 (stat.) +/- 0.7 (sys.) +/- 0.6 (theor.)) x 10^{-8}. We compare this result with predictions from chiral perturbation theory and estimates based on the decay K+ --> pi+ e+ e-.
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The first observation of the $D^0 to pi^+pi^-mu^+mu^-$ and $D^0 to K^+K^-mu^+mu^-$ decays is reported using a sample of proton-proton collisions collected by LHCb at a center-of-mass energy of 8$,$TeV, and corresponding to 2$,$fb$^{-1}$ of integrated luminosity. The corresponding branching fractions are measured using as normalization the decay $D^0 to K^- pi^+[mu^+mu^-]_{rho^0/omega}$, where the two muons are consistent with coming from the decay of a $rho^0$ or $omega$ meson. The results are $mathcal{B}(D^0 to pi^+pi^-mu^+mu^-)=(9.64pm0.48pm0.51pm0.97)times10^{-7}$ and $mathcal{B}(D^0 to K^+K^-mu^+mu^-)=( 1.54pm0.27pm0.09pm0.16)times10^{-7}$, where the uncertainties are statistical, systematic, and due to the limited knowledge of the normalization branching fraction. The dependence of the branching fraction on the dimuon mass is also investigated.
A discovery of the rare decay $B^{+} rightarrow pi^{+} mu^{+} mu^{-}$ is presented. This decay is observed for the first time, with 5.2 $sigma$ significance. The observation is made using $pp$ collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, collected with the LHCb detector. The measured branching fraction is (2.3 $pm$ 0.6 (stat.) $pm$ 0.1 (syst.))$times 10^{-8}$, and the ratio of the $B^{+} rightarrow pi^{+} mu^{+} mu^{-}$ and $B^{+} rightarrow K^{+} mu^{+} mu^{-}$ branching fractions is measured to be 0.053 $pm$ 0.014 (stat.) $pm$ 0.001 (syst.).
More than 400 $K^{+}topi^{+}mu^+mu^-$ events were observed in a rare $K^+$ decay experiment at the AGS. Normalized to the $K^{+}topi^{+}pi^+pi^-$ decay, the branching ratio is determined to be $(9.22 pm 0.60 (stat) pm 0.49 (syst))times 10^{-8}$. This branching ratio and the $mumu$ mass spectrum is in very good agreement with the measurement of the $K^{+}topi^{+}e^+e^-$ decay, but deviates significantly from the previous measurement.
First observations of the rare decays $B^+rightarrow K^+pi^+pi^-mu^+mu^-$ and $B^+rightarrow phi K^+mu^+mu^-$ are presented using data corresponding to an integrated luminosity of $3.0,{fb}^{-1}$, collected by the LHCb experiment at centre-of-mass energies of $7$ and $8mathrm{,TeV}$. The branching fractions of the decays are begin{eqnarray*} mathcal{B}(B^+rightarrow K^+pi^+pi^-mu^+mu^-) &=& (4.36,^{+0.29}_{-0.27},mathrm{(stat)}pm 0.21,mathrm{(syst)}pm0.18,mathrm{(norm)})times10^{-7}, mathcal{B}(B^+rightarrowphi K^+mu^+mu^-) &=& (0.82 ,^{+0.19}_{-0.17},mathrm{(stat)},^{+0.10}_{-0.04},mathrm{(syst)}pm0.27,mathrm{(norm)}) times10^{-7},end{eqnarray*} where the uncertainties are statistical, systematic, and due to the uncertainty on the branching fractions of the normalisation modes. A measurement of the differential branching fraction in bins of the invariant mass squared of the dimuon system is also presented for the decay $B^+rightarrow K^+pi^+pi^-mu^{+}mu^{-}$.
Using $(1310.6 pm 7.0) times 10^{6}~J/psi$ events acquired with the BESIII detector at the BEPCII storage rings, the decay $eta^primerightarrowpi^+pi^-mu^+mu^-$ is observed for the first time with a significance of 8$sigma$ via the process $J/psirightarrowgammaeta$. We measure the branching fraction of $eta^primerightarrowpi^+pi^-mu^+mu^-$ to be $mathcal{B}(eta^primerightarrowpi^+pi^-mu^+mu^-)$=(1.97$pm$0.33(stat.)$pm$0.18(syst.))$times10^{-5}$, where the first and second uncertainties are statistical and systematic, respectively.
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