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Register a new userObservation of the decay $Lambda^0_b to p K^- mu^+ mu^-$ and a search for $C!P$ violation
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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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A search for $C!P$ violation in $Lambda^0_b to p K^-$ and $Lambda^0_b to p pi^-$ decays is presented using a sample of $pp$ collisions collected with the LHCb detector and corresponding to an integrated luminosity of 3.0 fb$^{-1}$. The $C!P$-violating asymmetries are measured to be $A_{mathrm{CP}}^{pK^-} = -0.020 pm 0.013pm 0.019$ and $A_{mathrm{CP}}^{ppi^-} = -0.035 pm 0.017 pm 0.020 $, and their difference $A_{mathrm{CP}}^{pK^-}-A_{mathrm{CP}}^{ppi^-} = 0.014 pm 0.022 pm 0.010$, where the first uncertainties are statistical and the second systematic. These are the most precise measurements of such asymmetries to date.
A sensitive search for the lepton-number-violating decay $Xi^-to p mu^-mu^-$ has been performed using a sample of $sim10^9$ $Xi^-$ hyperons produced in 800 GeV/$c$ $p$-Cu collisions. We obtain $mathcal{B}(Xi^-to p mu^-mu^-)< 4.0times 10^{-8}$ at 90% confidence, improving on the best previous limit by four orders of magnitude.
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.
A search for the rare decay $Sigma^+ to p mu^+ mu^-$ is performed using $pp$ collision data recorded by the LHCb experiment at centre-of-mass energies $sqrt{s} = 7$ and $8$ TeV, corresponding to an integrated luminosity of $3 fb^{-1}$. An excess of events is observed with respect to the background expectation, with a signal significance of 4.1 standard deviations. No significant structure is observed in the dimuon invariant mass distribution, in contrast with a previous result from the HyperCP experiment. The measured $Sigma^+ to p mu^+ mu^-$ branching fraction is $(2.2,^{+,1.8}_{-,1.3})times 10^{-8}$, where statistical and systematic uncertainties are included, which is consistent with the Standard Model prediction.
We report the first evidence for the decay Sigma+ -> p mu+ mu- from data taken by the HyperCP experiment(E871) at Fermilab. Based on three observed events, the branching ratio is B(Sigma+ -> p,mu+,mu-) = [8.6 +6.6,-5.4(stat) +/-5.5(syst)] x 10**-8. The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Sigma+ -> p P0, P0 -> mu+ mu-, with a P0 mass of 214.3 +/- 0.5 MeV/c**2 and branching ratio B(Sigma+ -> p P0; P0 -> mu+ mu-) = [3.1 +2.4,-1.(stat) +/-1.5(syst)] x 10**-8.
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