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Register a new userSearch for the lepton number violating decays $B^{+}to pi^- mu^+ mu^+$ and $B^{+}to K^- mu^+ mu^+$
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A search is performed for the lepton number violating decay $B^{+}to h^- mu^+ mu^+$, where $h^-$ represents a $K^-$ or a $pi^-$, using data from the LHCb detector corresponding to an integrated luminosity of $36pb^{-1}$. The decay is forbidden in the Standard Model but allowed in models with a Majorana neutrino. No signal is observed in either channel and limits of $B(B^{+} to K^- mu^+ mu^+) < 5.4times 10^{-8}$ and $B(B^{+} to pi^- mu^+ mu^+) < 5.8times 10^{-8}$ are set at the 95% confidence level. These improve the previous best limits by factors of 40 and 30, respectively.
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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 $B^+rightarrow K^+pi^+pi^-mu^{+}mu^{-}$.
A search for heavy Majorana neutrinos produced in the $B^- to pi^+mu^-mu^-$ decay mode is performed using 3 fb$^{-1}$ of integrated luminosity collected with the LHCb detector in $pp$ collisions at center-of-mass energies of 7 TeV and 8 TeV at the LHC. Neutrinos with masses in the range 250-5000 MeV and lifetimes from zero to 1000 ps are probed. In the absence of a signal, upper limits are set on the branching fraction ${cal{B}}(B^- to pi^+mu^-mu^-)$ as functions of neutrino mass and lifetime. These limits are on the order of $10^{-9}$ for short neutrino lifetimes of 1 ps or less. Limits are also set on the coupling between the muon and a possible fourth-generation neutrino.
A search for the lepton-flavour violating decays $B^+ to K^+ {mu}^{pm} e^{mp}$ is performed using a sample of proton-proton collision data, collected with the LHCb experiment at centre-of-mass energies of $7$ and $8~{rm TeV}$ and corresponding to an integrated luminosity of 3$rm~fb^{-1}$. No significant signal is observed, and upper limits on the branching fractions are set as $mathcal{B}(B^+ to K^+ {mu}^- e^+) < 7.0~(9.5) times 10^{-9}$ and $mathcal{B}(B^+ to K^+ {mu}^+ e^-) < 6.4~(8.8) times 10^{-9}$ at 90 (95) % confidence level. The results improve the current best limits on these decays by more than one order of magnitude.
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.
A search for the lepton flavour violating decay $tau^-to mu^-mu^+mu^-$ is performed with the LHCb experiment. The data sample corresponds to an integrated luminosity of $1.0mathrm{,fb}^{-1}$ of proton-proton collisions at a centre-of-mass energy of $7mathrm{,Tekern -0.1em V}$ and $2.0mathrm{,fb}^{-1}$ at $8mathrm{,Tekern -0.1em V}$. No evidence is found for a signal, and a limit is set at $90%$ confidence level on the branching fraction, $mathcal{B}(tau^-to mu^-mu^+mu^-) < 4.6 times 10^{-8}$.
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