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Register a new userImproved limit on the branching fraction of the rare decay $K^0_{scriptscriptstyle S}tomu^+mu^-$
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A search for the decay $K^0_{scriptscriptstyle S}tomu^+mu^-$ is performed, based on a data sample of proton-proton collisions corresponding to an integrated luminosity of 3 fb$^{-1}$, collected by the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yield is consistent with the background-only hypothesis, yielding a limit on the branching fraction of ${cal B}(K^0_{scriptscriptstyle S}tomu^+mu^-) < 0.8~(1.0) times 10^{-9}$ at $90%~(95%)$ confidence level. This result improves the previous upper limit on the branching fraction by an order of magnitude.
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A search for the decay $K^0_{mathrm{S}}rightarrowmu^{+}mu^{-}$ is performed using proton-proton collision data, corresponding to an integrated luminosity of $5.6,text{fb}^{-1}$ and collected with the LHCb experiment during 2016, 2017 and 2018 at a center-of-mass energy of $13,mathrm{TeV}$. The observed signal yield is consistent with zero, yielding an upper limit of ${cal B}(K^0_{mathrm{S}}rightarrowmu^{+}mu^{-}) < 2.2 times 10^{-10}$ at 90% CL. The limit reduces to ${cal B}(K^0_{mathrm{S}}rightarrowmu^{+}mu^{-}) < 2.1 times 10^{-10}$ at 90% CL once combined with the result from data taken in 2011 and 2012.
The charmless three-body decays $B^0_{(s)} to K_{mathrm{scriptscriptstyle S}}^0 h^+ h^{prime -}$ (where $h^{(prime)} = pi, K$) are analysed using a sample of $pp$ collision data recorded by the LHCb experiment, corresponding to an integrated luminosity of $3mbox{fb}^{-1}$. The branching fractions are measured relative to that of the $B^0 to K_{mathrm{scriptscriptstyle S}}^0 pi^{+} pi^{-}$ decay, and are determined to be: begin{eqnarray*} frac{{cal B}(B^0rightarrow K^0_{rm S}K^{pm}pi^{mp})}{{cal B}(B^0rightarrow K^0_{rm S}pi^{+}pi^{-})} = {} & 0.123 pm 0.009 ; mathrm{,(stat)}; pm 0.015 ; mathrm{,(syst)},, frac{{cal B}(B^0rightarrow K^0_{rm S}K^{+}K^{-})} {{cal B}(B^0rightarrow K^0_{rm S}pi^{+}pi^{-})} = {} & 0.549 pm 0.018 ; mathrm{,(stat)}; pm 0.033 ; mathrm{,(syst)},, frac{{cal B}(B_{s}^0rightarrow K^0_{rm S}pi^{+}pi^{-})}{{cal B}(B^0rightarrow K^0_{rm S}pi^{+}pi^{-})} = {} & 0.191 pm 0.027 ; mathrm{,(stat)}; pm 0.031 ; mathrm{,(syst)}; pm 0.011 ; (f_s/f_d) ,, frac{{cal B}(B_{s}^0rightarrow K^0_{rm S}K^{pm}pi^{mp})} {{cal B}(B^0rightarrow K^0_{rm S}pi^{+}pi^{-})} = {} & 1.70phantom{0} pm 0.07phantom{0} ; mathrm{,(stat)} ; pm 0.11phantom{0} ; mathrm{,(syst)}; pm 0.10phantom{0} ; (f_s/f_d) ,, frac{{cal B}(B_{s}^0rightarrow K^0_{rm S}K^{+}K^{-})}{{cal B}(B^0rightarrow K^0_{rm S}pi^{+}pi^{-})} in {} & [0.008 - 0.051] rm ~at~90%~confidence~level, end{eqnarray*} where $f_s/f_d$ represents the ratio of hadronisation fractions of the $B^0_s$ and $B^0$ mesons.
The processes $e^+e^-to K^0_{scriptscriptstyle S}K^pmpi^{mp}pi^0$ and $e^+e^-to K^0_{scriptscriptstyle S}K^pmpi^{mp}eta$ are studied over a continuum of energies from threshold to 4 GeV with the initial-state photon radiation method. Using 454 fb$^{-1}$ data collected with the BABAR detector at the SLAC PEP-II storage ring, the first measurements of the cross sections for these processes are obtained. The intermediate resonance structures from $K^{*0}(Kpi)^0$, $K^{*}(892)^pm(Kpi)^mp$ and $K^0_{scriptscriptstyle S}K^pmrho^{mp}$ are studied. The $J/psi$ is observed in all of these channels, and corresponding branching fractions are measured.
The angular distribution and differential branching fraction of the decay $B^{+} rightarrow K^{+}mu^{+}mu^{-}$ are studied with a dataset corresponding to $1.0,mathrm{fb}^{-1}$ 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 $mathcal{B}(B^{+} rightarrow K^{+}mu^{+}mu^{-}) = (4.36 pm 0.15 pm 0.18)times 10^{-7}$. These measurements are the most precise to date of the $B^{+} rightarrow K^{+}mu^{+}mu^{-}$ decay.
Based on 586 $rm{pb^{-1}}$ of $e^+e^-$ annihilation data collected at a center-of-mass energy of $sqrt{s}=4.6~rm{GeV}$ with the BESIII detector at the BEPCII collider, the absolute branching fraction of $Lambda_c^+ to p K^0_{mathrm{S}}eta$ decays is measured for the first time to be $mathcal{B}(Lambda_c^+ to p K^0_{mathrm{S}}eta) = (0.414 pm 0.084 pm 0.028)%$, where the first uncertainty is statistical and the second is systematic. The result is compatible with a previous CLEO result on the relative branching fraction $frac{mathcal{B}(Lambda_c^+ to p K^0_{mathrm{S}}eta)}{mathcal{B}(Lambda_c^+ to p K^-pi^+)}$, and consistent with theoretical predictions of SU(3) flavor symmetry.
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