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Register a new userObservation of the semileptonic decay $B^{+}to poverline{p}mu^{+} u_{mu}$
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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.
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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.).
We observe a net beam-excess of $8.7 pm 6.3$ (stat) $pm 2.4$ (syst) events, above 160 MeV, resulting from the charged-current reaction of $ u_{mu}$ and/or $bar u_{mu}$ on C and H in the LSND detector. No beam related muon background is expected in this energy regime. Within an analysis framework of $pi^0 to u_{mu}bar u_{mu}$, we set a direct upper limit for this branching ratio of $Gamma(pi^0 to u_mu bar u_mu) / Gamma(pi^0 to all) < 1.6 times 10^{-6}$ at 90% confidence level.
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.
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 search for $C!P$ violation in the decay $Lambda^0_b to p K^- mu^+ mu^-$ is presented. This decay is mediated by flavour-changing neutral-current transitions in the Standard Model and is potentially sensitive to new sources of $C!P$ violation. The study is based on a data sample of proton-proton collisions recorded with the LHCb experiment, corresponding to an integrated luminosity of $3$ $mathrm{fb}^{-1}$. The $Lambda^0_b to p K^- mu^+ mu^-$ decay is observed for the first time, and two observables that are sensitive to different manifestations of $C!P$ violation are measured, $Deltamathcal{A}_{C!P} equiv mathcal{A}_{C!P}(Lambda^0_b to p K^- mu^+ mu^-)-mathcal{A}_{C!P}(Lambda^0_bto pK^- J/psi)$ and $a_{C!P}^{widehat{T}-odd}$, where the latter is based on asymmetries in the angle between the $mu^+mu^-$ and $p K^-$ decay planes. These are measured to be $Deltamathcal{A}_{C!P} = (-3.5 pm 5.0(stat) pm 0.2(syst))times 10^{-2}$, $a_{C!P}^{widehat{T}-odd} = (1.2 pm 5.0(stat) pm 0.7(syst))times 10^{-2}$, and no evidence for $C!P$ violation is found.
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