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Register a new userNew limit on the lepton-flavour violating decay mu -> e gamma
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We present a new result based on an analysis of the data collected by the MEG detector at the Paul Scherrer Institut in 2009 and 2010, in search of the lepton flavour violating decay mu->e gamma. The likelihood analysis of the combined data sample, which corresponds to a total of 1.8 x 10**14 muon decays, gives a 90% C.L. upper limit of 2.4 x 10**-12 on the branching ratio of the mu->e gamma decay, constituting the most stringent limit on the existence of this decay to date.
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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 for the decay mu -> e gamma, performed at PSI and based on data from the initial three months of operation of the MEG experiment, yields an upper limit on the branching ratio of BR(mu -> e gamma) < 2.8 x 10**-11 (90% C.L.). This corresponds to the measurement of positrons and photons from ~ 10**14 stopped mu-decays by means of a superconducting positron spectrometer and a 900 litre liquid xenon photon detector.
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.
The MEG Experiment searches for a lepton flavour violating decay, $mu^+tomathrm{e}^+gamma $, with a branching-ratio sensitivity of $10^{-13}$ in order to explore the parameter region predicted by many theoretical models beyond the Standard Model. Detector construction and the Engineering Run were completed in 2007, and the first Physics Run will be carried out in 2008. In this paper, the prospects of MEG Physics Run in 2008 is described in addition to the experimental overview.
A search for the lepton-flavour violating decay $D^0 to e^pm mu^mp$ is made with a dataset corresponding to an integrated luminosity of 3.0 fb$^{-1}$ of proton-proton collisions at centre-of-mass energies of $7$ TeV and $8$ TeV, collected by the LHCb experiment. Candidate $D^0$ mesons are selected using the decay $D^{*+} to D^0 pi^+$ and the $D^0 to e^pm mu^mp$ branching fraction is measured using the decay mode $D^0 to K^-pi^+$ as a normalisation channel. No significant excess of $D^0 to e^pm mu^mp$ candidates over the expected background is seen, and a limit is set on the branching fraction, $mathcal{B}(D^0 to e^pm mu^mp) < 1.3 times 10^{-8}$, at 90 % confidence level. This is an order of magnitude lower than the previous limit and it further constrains the parameter space in some leptoquark models and in supersymmetric models with R-parity violation.
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