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Register a new userSearch for the Lepton-Number-Violating Decay $Xi^- to p mu^- mu^-$
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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.
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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, $mathcal{B}(tau^-to mu^-mu^+mu^-) < 4.6 times 10^{-8}$.
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.
Lepton-flavour violating tau-decays are predicted in many extensions of the Standard Model at a rate observable at future collider experiments. In this article we focus on the decay tau to mu mu antimu, which is a promising channel to observe lepton-flavour violation at the Large Hadron Collider LHC. We present analytic expressions for the differential decay width derived from a model-independent effective Lagrangian with general four-fermion operators, and estimate the experimental acceptance for detecting the decay tau to mu mu antimu at the LHC. Specific emphasis is given to decay angular distributions and how they can be used to discriminate new physics models. We provide specific predictions for various extensions of the Standard Model, including supersymmetric, little Higgs and technicolour models.
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 have searched for the lepton-flavor-violating decay $B^{0}to K^{ast 0} mu^{pm} e^{mp}$ using a data sample of 711 $fb^{-1}$ that contains $772 times 10^{6}$ $Bbar{B}$ pairs. The data were collected near the $Upsilon (4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. No signals were observed, and we set 90% confidence level upper limits on the branching fractions of ${cal B}(B^{0}to K^{ast 0} mu^{+} e^{-})< 1.2times 10^{-7}$, ${cal B}(B^{0}to K^{ast 0} mu^{-} e^{+})< 1.6times 10^{-7}$, and, for both decays combined, ${cal B}(B^{0}to K^{ast 0} mu^{pm} e^{mp}) < 1.8times 10^{-7}$. These are the most stringent limits on these decays to date.
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