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Register a new userSearches for violation of lepton flavour and baryon number in tau lepton decays at LHCb
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Searches for the lepton flavour violating decay $tau^-rightarrow mu^-mu^+mu^-$ and the lepton flavour and baryon number violating decays $tau^-rightarrow bar{p}mu^+mu^-$ and $tau^-rightarrow pmu^-mu^-$ have been carried out using proton-proton collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, taken by the LHCb experiment at $sqrt{s} = 7$ TeV. No evidence has been found for any signal, and limits have been set at 90% confidence level on the branching fractions: $cal B(tau^-rightarrow mu^-mu^+mu^-) < 8.0 times 10^{-8}$, $cal B(tau^-rightarrow bar{p}mu^+mu^-) < 3.3 times 10^{-7}$ and $cal B(tau^-rightarrow pmu^-mu^-) < 4.4 times 10^{-7}$. The results for the $tau^-rightarrow bar{p}mu^+mu^-$ and $tau^-rightarrow pmu^-mu^-$ decay modes represent the first direct experimental limits on these channels.
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We search for lepton-number- and baryon-number-violating decays $tau^{-}tooverline{p}e^{+}e^{-}$, $pe^{-}e^{-}$, $overline{p}e^{+}mu^{-}$, $overline{p}e^{-}mu^{+}$, $overline{p}mu^{+}mu^{-}$, and $pmu^{-}mu^{-}$ using 921 fb$^{-1}$ of data, equivalent to $(841pm12)times 10^6$ $tau^{+}tau^{-}$ events, recorded with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. In the absence of a signal, $90%$ confidence-level upper limits are set on the branching fractions of these decays in the range $(1.8$-$4.0)times 10^{-8}$. We set the worlds first limits on the first four channels and improve the existing limits by an order of magnitude for the last two channels.
The coupling of the electroweak gauge bosons of the Standard Model (SM) to leptons is flavour universal. Extensions of the SM do not necessarily have this property. Rare decays of heavy flavour are suppressed in the SM and new particles may give sizeable contributions to these processes, therefore, their precise study allows for sensitive tests of lepton flavour universality. Of particular interest are rare b to sll decays that are well accessible at the LHCb experiment. Recent results from LHCb on lepton flavour universality in rare b to sll decays are discussed.
We study Lepton Flavour Violating hadron decays of the tau lepton within the Simplest Little Higgs model. Namely we consider $tau rightarrow mu (P, V, PP)$ where $P$ and $V$ are short for a pseudoscalar and a vector meson. We find that, in the most positive scenarios, branching ratios for these processes are predicted to be, at least, four orders of magnitude smaller than present experimental bounds.
We did a model independent phenomenological study of baryogenesis via leptogenesis, neutrinoless double beta decay (NDBD) and charged lepton flavour violation (CLFV) in a generic left-right symmetric model (LRSM) where neutrino mass originates from the type I + type II seesaw mechanism. We studied the new physics contributions to NDBD coming from the left-right gauge boson mixing and the heavy neutrino contribution within the framework of LRSM. We have considered the mass of the RH gauge boson to be specifically 5 TeV, 10 TeV and 18 TeV and studied the effects of the new physics contributions on the effective mass and baryogenesis and compared with the current experimental limit. We tried to correlate the cosmological BAU from resonant leptogenesis with the low energy observables, notably, NDBD and LFV with a view to finding a common parameter space where they coexists.
Lepton flavour violation (LFV) naturally occurs in many new physics models, specifically in those explaining the $B$ anomalies. While LFV has already been studied for mesonic decays, it is important to consider also baryonic decays mediated by the same quark transition. In this paper, we study LFV in the baryonic $Lambda_b to Lambda ell_1 ell_2$ using for the first time a full basis of New Physics operators. We present expected bounds on the branching ratio in a model-independent framework and using two specific new physics models. Finally, we point out the interplay and orthogonality between the baryonic and mesonic LFV searches.
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