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Register a new user$B^0_{s} rightarrow mu^+mu^-$ at LHC
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Flavio Archilli
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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.
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oindent A search for the decays $B^0_{s}rightarrow mu^+ mu^- mu^+ mu^-$ and $B^0 rightarrow mu^+ mu^- mu^+ mu^-$ is performed using data, corresponding to an integrated luminosity of 1.0ensuremath{{,fb}^{-1}}xspace, collected with the LHCb detector in 2011. The number of candidates observed is consistent with the expected background and, assuming phase-space models of the decays, limits on the branching fractions are set: {${ensuremath{cal B}xspace}(B^0_{s}rightarrow mu^+ mu^- mu^+ mu^-) < 1.6 (1.2) times 10^{-8}$} and {${ensuremath{cal B}xspace}(B^0 rightarrow mu^+ mu^- mu^+ mu^-)< 6.6 (5.3) times 10^{-9}$} at 95,% (90,%) confidence level. In addition, limits are set in the context of a supersymmetric model which allows for the $B^0_{(s)}$ meson to decay into a scalar ($S$) and pseudoscalar particle ($P$), where $S$ and $P$ have masses of 2.5 GeV and 214.3 MeV, respectively, both resonances decay into $mu^+mu^-$. The branching fraction limits for these decays are {${ensuremath{cal B}xspace}(ensuremath{B^0_{s}rightarrow SP}xspace) < 1.6 (1.2) times 10^{-8}$} and {${ensuremath{cal B}xspace}(ensuremath{B^0rightarrow SP}xspace)< 6.3 (5.1) times 10^{-9}$} at 95% (90%) confidence level.
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.
A search for the lepton-flavour violating decays $B^0_s rightarrow e^pm mu^mp$ and $B^0 rightarrow e^pm mu^mp$ is performed based on a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb$^{-1}$, collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yields are consistent with the background-only hypothesis. Upper limits on the branching fractions are determined to be $mathcal{B}(B^0_s rightarrow e^pm mu^mp) < 5.4,(6.3) times 10^{-9}$ and $mathcal{B}(B^0 rightarrow e^pm mu^mp) < 1.0,(1.3) times 10^{-9}$ at $90%,(95%)$ confidence level, which are the strongest limits on these decays to date.
Transitions of the type $b to s l^+ l^-$ are flavour changing neutral current processes where new physics can enter in competing loop diagrams with respect to the Standard Model contributions. In these decays several observables sensitive to new physics, and where theoretical uncertainties are under control, can be constructed. Particularly interesting are the angular asymmetries in the decay $B_d to K^* mu^+ mu^-$ and the measurement of the branching fraction of the decays $B_{s,d} to mu^+ mu^-$. Recent measurements of these observables and the measurement of the isospin asymmetry in the decays $B to K^{(*)} mu^+ mu^-$ are presented.
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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