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Register a new userMeasurement of the decay phi->mu+mu-
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The process e^+e^- ->mu^+mu^- has been studied with SND detector at VEPP-2M e^+e^- collider in the vicinity of phi(1020) resonance. The product of branching ratios of phi meson into leptons sqrt{B(phi->mu^+mu^-) B(phi-> e^+e^-)}=(3.14+-0.22+-0.14)x10^{-4} was measured from the interference in the cross section of the process e^+e^- ->mu^+mu^-. The branching ratio B(phi->mu^+mu^-)=(3.30+-0.45+-0.32)x10^{-4} was obtained.
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We have observed $23.2 pm 6.0_{-0.9}^{+1.0}$ purely-leptonic decays of $D_s^+ -> mu^+ u_mu$ from a sample of muonic one prong decay events detected in the emulsion target of Fermilab experiment E653. Using the $D_s^+ -> phi mu^+ u_mu$ yield measured previously in this experiment, we obtain $B(D_s^+ --> mu^+ u_mu) / B(D_s^+ --> phi mu^+ u_mu) =0.16 pm 0.06 pm 0.03$. In addition, we extract the decay constant $f_{D_s}=194 pm 35 pm 20 pm 14 MeV$.
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.
A search for the rare leptonic decay $B^{+} rightarrow {mu}^{+}{mu}^{-}{mu}^{+}{ u}_{{mu}}$ is performed using proton-proton collision data corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ collected by the LHCb experiment. The search is carried out in the region where the lowest of the two ${mu}^{+}{mu}^{-}$ mass combinations is below $980$MeV/c$^{2}$. The data are consistent with the background-only hypothesis and an upper limit of $1.6 times 10^{-8}$ at 95% confidence level is set on the branching fraction in the stated kinematic region.
The shape of the $B_s^0rightarrow D_s^{*-}mu^+ u_{mu}$ differential decay rate is obtained as a function of the hadron recoil using proton-proton collision data at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 1.7 fb$^{-1}$ collected by the LHCb detector. The $B_s^0rightarrow D_s^{*-}mu^+ u_{mu}$ decay is reconstructed through the decays $D_s^{*-}rightarrow D_s^{-}gamma$ and $D_s^{-}rightarrow K^-K^+pi^-$. The differential decay rate is fitted with the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) parametrisations of the form factors, and the relevant quantities for both are extracted.
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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