Search for decays of neutral beauty mesons into four muons

A search for the non-resonant decays $B^0_s rightarrow mu^{+}mu^{-}mu^{+}mu^{-}$ and $B^0 rightarrow mu^{+}mu^{-}mu^{+}mu^{-}$ is presented. The measurement is performed using the full Run 1 data set collected in proton-proton collisions by the LHCb experiment at the LHC. The data correspond to integrated luminosities of $1$ and $2~mathrm{fb}^{-1}$ collected at centre-of-mass energies of $7$ and $8~mathrm{TeV}$, respectively. No signal is observed and upper limits on the branching fractions of the non-resonant decays at $95%$ confidence level are determined to be mathcal{B}(B^0_s rightarrow mu^{+}mu^{-}mu^{+}mu^{-}) & < 2.5 times 10^{-9} mathcal{B}(B^0 rightarrow mu^{+}mu^{-}mu^{+}mu^{-}) & < 6.9 times 10^{-10}.

Angular analysis of charged and neutral $B to K mu^+mu^-$ decays

The angular distributions of the rare decays $B^+ to K^+mu^+mu^-$ and $B^0 to K^0_{rmscriptscriptstyle S}mu^+mu^-$ are studied with data corresponding to 3$~$fb$^{-1}$ of integrated luminosity, collected in proton-proton collisions at 7 and 8$~$TeV centre-of-mass energies with the LHCb detector. The angular distribution is described by two parameters, $F_{rm H}$ and the forward-backward asymmetry of the dimuon system $A_{rm FB}$, which are determined in bins of the dimuon mass squared. The parameter $F_{rm H}$ is a measure of the contribution from (pseudo)scalar and tensor amplitudes to the decay width. The measurements of $A_{rm FB}$ and $F_{rm H}$ reported here are the most precise to date and are compatible with predictions from the Standard Model.

New resonances in B-meson decays

The X(3872) and Y(3940) properties and decay modes from Belle are reviewed and the results on a search for the decay $B^+ra h_c K^+$, $h_cra eta_c gamma$ at Belle are presented.

Study of X(3872) in $B$ meson decays

We present results on the X(3872), produced in $B^+ to X(3872) K^+$ and $B^0 to X(3872) K^0_S$ decays where $X(3872) to J/psi pi^+ pi^-$. We report the first statistically significant observation of $B^0 to X(3872) K^0_S$ and measure the ratio of branching fractions to be $frac{{cal B}(B^0 to X(3872)K^0)} {{cal B}(B^+ to X(3872)K^+)} = 0.82 pm 0.22 pm 0.05$, consistent with unity. The mass difference between the X(3872) states produced in $B^+$ and $B^0$ decay is found to be $delta M equiv M_{XK^+} - M_{XK^0} = (+0.18 pm 0.89 pm 0.26)$ MeV/$c^2$, consistent with zero. In addition, we search for the X(3872) in the decay $B^0 to X(3872)K^+pi^-$, $X(3872) to J/psi pi^+ pi^-$. We measure ${cal B}(B^0 to X(3872) (K^+ pi^-)_{NR}) times {cal B}(X(3872) to J/psi pi^+ pi^-) = (8.1 pm 2.0 ^{+1.1}_{-1.4})times 10^{-6}$ and we set the 90% C.L. limit, ${cal B}(B^0 to X(3872)K^{*}(892)^0) times {cal B}(X(3872) to J/psi pi^+ pi^-) < 3.4 times 10^{-6}$. The analysis is based on a 605 fb$^{-1}$ data sample collected at the $Upsilon(4S)$ with the Belle detector at the KEKB collider.

Measurement of eta meson decays into lepton-antilepton pairs

A search for rare lepton decays of the eta meson was performed using the WASA detector at CELSIUS. Two candidates for double Dalitz decay eta->e+e-e+e- events are reported with a background of 1.3+/-0.2 events. This allows to set an upper limit to the branching ratio of 9.7E-5 (90% CL). The branching ratio for the decay eta->e+e-gamma is determined to (7.8+/-0.5 stat+/-0.8 syst)E-3. An upper limit (90% CL) for the branching ratio for the eta->e+e- decay is 2.7E-5 and a limit for the sum of the eta->mu+mu-mu+mu- and eta->pi+pi-mu+mu- decays is 3.6E-4.