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Register a new userImplication of possible observation of enhanced Bd0 --> mu+ mu- decay
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The very rare Bd0 --> mu+ mu- decay may be the last chance for New Physics in flavor sector at the LHC, before the 13 TeV run in 2015. Partially motivated by the known tension in sin(2beta/phi_1), enhancement beyond (3-4) x 10^-10 would likely imply the effect of a fourth generation of quarks. If observed at this level, the 126 GeV boson may not be the actual Higgs boson, while the b --> d quadrangle (modulo m_t) would jump out. The 2011-2012 data is likely not sensitive to values below 3 x 10^-10, and the mode should continue to be pursued with the 13 TeV run.
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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-.
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.).
The Cabibbo-suppressed semileptonic decay $B^{+}to poverline{p}mu^{+} u_{mu}$ is observed for the first time using a sample of $pp$ collisions corresponding to an integrated luminosity of 1.0, 2.0 and 1.7fb$^{-1}$ at centre-of-mass energies of 7, 8 and 13TeV, respectively. The differential branching fraction is measured as a function of the $poverline{p}$ invariant mass using the decay mode $B^{+}to J/psi K^{+}$ for normalisation. The total branching fraction is measured to be begin{align*} mathcal{B}(B^{+}to poverline{p}mu^{+} u_{mu}) = (5.27 ^{+0.23}_{-0.24} pm 0.21 pm 0.15)times 10^{-6}, end{align*} where the first uncertainty is statistical, the second systematic and the third is from the uncertainty on the branching fraction of the normalisation channel.
The suppressed decay $Lambda^{0}_{b}rightarrow ppi^{-}mu^{+}mu^{-}$, excluding the $J/psi$ and $psi(2S)rightarrow mu^{+}mu^{-}$ resonances, is observed for the first time with a significance of 5.5 standard deviations. The analysis is performed with proton-proton collision data corresponding to an integrated luminosity of $3mathrm{fb}^{-1}$ collected with the LHCb experiment. The $Lambda^{0}_{b}rightarrow ppi^{-}mu^{+}mu^{-}$ branching fraction is measured relative to the $Lambda^{0}_{b}rightarrow J/psi(rightarrow mu^{+}mu^{-})ppi^{-}$ branching fraction giving begin{align} onumber frac{mathcal{B}(Lambda^{0}_{b}rightarrow ppi^{-}mu^{+}mu^{-})}{mathcal{B}({Lambda^{0}_{b}rightarrow J/psi(rightarrow mu^{+}mu^{-})ppi^{-}})} &= 0.044pm0.012pm0.007, end{align} where the first uncertainty is statistical and the second is systematic. This is the first observation of a $brightarrow d$ transition in a baryonic decay.
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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