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Register a new userAbsolute Branching Ratio Normalization for Rare pi+ and mu+ Decays in the PIBETA Experiment
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E. Frlez
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We have used the PIBETA detector at the PSI for a precise measurement of rare pion and muon weak decays. We have collected a large statistical sample of (1) pi+ -> e+ nu, (2) pi+ -> pi0 e+ nu, (3) pi+ -> e+ nu gamma, (4) mu+ -> e+ nu nu, and (5) mu+ -> e+ nu nu gamma decays. We have evaluated the absolute branching ratios for these processes by normalizing to the independently measured number of decaying pi+s (or mu+s). We discuss the mutual consistency of the preliminary results.
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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 $B^+rightarrow K^+pi^+pi^-mu^{+}mu^{-}$.
We have searched with the KLOE detector for the P and CP violating decay eta -> pi^+pi^- in a sample of 1.55 x 10^7 etas from the decay phi -> eta gamma of phi mesons produced in e+e- annihilations at DAFNE. No signal is found. We obtain the upper limit BR(eta -> pi^+pi^-) < 1.3 x 10^-5 at 90% confidence level.
A search for the decays Bs -> mu+ mu- and B0 -> mu+ mu- is performed with 0.37 fb^-1 of pp collisions at sqrt{s} = 7 TeV collected by the LHCb experiment in 2011. The upper limits on the branching fractions are BR (Bs -> mu+ mu-) < 1.6 x 10^-8 and BR(B0 -> mu+ mu-) < 3.6 x 10^-9 at 95% confidence level. A combination of these results with the LHCb limits obtained with the 2010 dataset leads to BR (Bs -> mu+ mu-) < 1.4 x 10^-8 and BR (B0 -> mu+ mu-) < 3.2 x 10^-9 at 95% confidence level.
A search for the rare decays $B_s^0 to pi^+pi^-mu^+mu^-$ and $B^0 to pi^+pi^-mu^+mu^-$ is performed in a data set corresponding to an integrated luminosity of 3.0 fb$^{-1}$ collected by the LHCb detector in proton-proton collisions at centre-of-mass energies of 7 and 8 TeV. Decay candidates with pion pairs that have invariant mass in the range 0.5-1.3 GeV/$c^2$ and with muon pairs that do not originate from a resonance are considered. The first observation of the decay $B_s^0 to pi^+pi^-mu^+mu^-$ and the first evidence of the decay $B^0 to pi^+pi^-mu^+mu^-$ are obtained and the branching fractions, restricted to the dipion-mass range considered, are measured to be $mathcal{B}(B_s^0 to pi^+pi^-mu^+mu^-)=(8.6pm 1.5,({rm stat}) pm 0.7,({rm syst})pm 0.7,({rm norm}))times 10^{-8}$ and $mathcal{B}(B^0 to pi^+pi^-mu^+mu^-)=(2.11pm 0.51,({rm stat}) pm 0.15,({rm syst})pm 0.16,({rm norm}) )times 10^{-8}$, where the third uncertainty is due to the branching fraction of the decay $B^0to J/psi(to mu^+mu^-)K^*(890)^0(to K^+pi^-)$, used as a normalisation.
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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