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Nicola Serra
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The ATLAS, CMS and LHCb experiments will perform extensive searches for physics Beyond the Standard Model (BSM). The investigation of decays of beauty hadrons represents an alternative and complementary approach to the direct BSM searches. A particularly promising observable for the search of New Physics (NP) in $B-$hadron decays, is the measurement of the branching ratio of the decay $B_Sto mu^{+} mu^{-}$. This observable is sensitive to physics BSM with new scalar or pseudoscalar effective operators, such as theories involving an extended Higgs sector. Here the prospects of the ATLAS, CMS and the LHCb experiments for such a measurement are discussed. In particular the LHCb experiment, thanks to its good particle identification and momentum resolution, has the potential for an early discovery of this decay.
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With their 2010-2011 data set, the LHC experiments have started their quest to observe the rare decays B0_{s/d} -> mu+ mu-. This study will provide very sensitive probes of New Physics (NP) effects. NP discovery potential lies as well in the study of the decay B0_d -> K*0 mu+ mu-. Results and perspectives are presented for studies at the LHC of rare B decays involving flavor changing neutral currents.
Rare leptonic decays of $B_{(s)}^0$ mesons are sensitive probes of New Physics effects. A combination of the CMS and LHCb analyses on the search of the rare decays $B_{s}^0 rightarrow mu^+mu^-$ and $B^0 rightarrow mu^+mu^-$ is presented. The branching fractions of $B_{s}^0 rightarrow mu^+mu^-$ and $B^0 rightarrow mu^+mu^-$ are measured to be $mathcal{B}(B_{s}^0 rightarrow mu^+mu^-) = (2.8 ,^{+0.7}_{-0.6}) times 10^{-9}$ and $mathcal{B}(B^0 rightarrow mu^+mu^-) = (3.9 ,^{+1.6}_{-1.4}) times 10^{-10}$ respectively. A statistical significances of $6.2,sigma$ is evaluated for $B_{s}^0 rightarrow mu^+mu^-$ from the Wilks theorem while a significance of $3.0, sigma$ is measured for $B^0 rightarrow mu^+mu^-$ from the Feldman-Cousins procedure.
The pure leptonic decay B_s -> mu mu is strongly suppressed in the Standard Model (SM), but can have large enhancements in Supersymmetry, especially at large values of tanbe. New limits on this decay channel from recent LHC data have been used to claim that these limits restrict the SUSY parameter space even more than the direct searches. However, direct searches are hardly dependent on tanbe, while BR(B_s -> mu mu) is proportional to tanbe^6. The relic density constraint requires large tanbe in a large region of the parameter space, which can lead to large values of B_s -> mu mu. Nevertheless, the experimental upper limit on BR(B_s -> mu mu) is not constraining the parameter space of the CMSSM more than the direct searches and the present Higgs limits, if combined with the relic density. We also observe SUSY parameter regions with negative interferences, where the B_s -> mu mu value is up to a factor three below the SM expectation, even at large values of tanbe.
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 leptonic decay $B^{+} rightarrow {mu}^{+}{mu}^{-}{mu}^{+}{ u}_{{mu}}$ is performed using proton-proton collision data corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ collected by the LHCb experiment. The search is carried out in the region where the lowest of the two ${mu}^{+}{mu}^{-}$ mass combinations is below $980$MeV/c$^{2}$. The data are consistent with the background-only hypothesis and an upper limit of $1.6 times 10^{-8}$ at 95% confidence level is set on the branching fraction in the stated kinematic region.
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