Search for a massive invisible particle $X^0$ in $B^{+}to e^{+}X^{0}$ and $B^{+}to mu^{+}X^{0}$ decays

We present a search for a non-Standard-Model invisible particle $X^0$ in the mass range $0.1textrm{-}1.8 ,{rm GeV}/{c^2}$ in $B^{+}to e^{+} X^{0}$ and $B^{+}to mu^{+} X^{0}$ decays. The results are obtained from a $711~{rm fb}^{-1}$ data sample that corresponds to $772 times 10^{6} Bbar{B}$ pairs, collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. One $B$ meson is fully reconstructed in a hadronic mode to determine the momentum of the lepton of the signal decay in the rest frame of the recoiling partner $B$ meson. We find no evidence of a signal and set upper limits on the order of $10^{-6}$.

Measurement of the $B^0$--$bar B^0$ oscillation frequency $Delta m_d$ with the decays $B^0 to D^- pi^+$ and $B^0 to J/ psi K^{*0}$

The $B^0$--$bar B^0$ oscillation frequency $Delta m_d$ is measured by the LHCb experiment using a dataset corresponding to an integrated luminosity of $1.0,$fb$^{-1}$ of proton-proton collisions at $sqrt{s} = 7,$TeV, and is found to be $Delta m_d = 0.5156 pm 0.0051,($stat.$) pm 0.0033,($syst.$),$ps$^{-1}$. The measurement is based on results from analyses of the decays $B^0 to D^- pi^+$ ($D^- to K^+ pi^- pi^-$) and $B^0 to J/ psi K^{*0}$ ($ J/ psi to mu^+ mu^-$, $K^{*0} to K^+ pi^-$) and their charge conjugated modes.

Measurement of the $B^0 rightarrow K^{*0}e^+e^-$ branching fraction at low dilepton mass

The branching fraction of the rate decay $B^0 rightarrow K^{*0}e^+e^-$ in the dilepton mass region from 30 to 1000 MeV$/c^2$ has been measured by the LHCb experiment, using $pp$ collision data, corresponding to an integrated luminosity of 1.0 fb$^{-1}$, at a centre-of-mass energy of 7 TeV. The decay mode $B^0 rightarrow J/psi(e^+e^-) K^{*0}$ is utilized as a normalization channel. The branching fraction $B^0 rightarrow K^{*0}e^+e^-$ is measured to be $$ B(B^0 rightarrow K^{*0}e^+e^-)^{30-1000 MeV/c^2}= (3.1, ^{+0.9mbox{} +0.2}_{-0.8mbox{}-0.3} pm 0.2)times 10^{-7}, $$ where the first error is statistical, the second is systematic, and the third comes from the uncertainties on the B^0 rightarrow J/psi K^{*0}$ and $J/psi rightarrow e^+e^- $ branching fractions.

Measurement of CP asymmetries in $B^0 to K^0pi^0$ decays

We report measurements of CP violation parameters in $B^0 to K^0 pi^0$ decays based on a data sample of $657 times 10^6 Bbar{B}$ pairs collected with the Belle detector at the KEKB $e^+ e^-$ asymmetric-energy collider. We use $B^0 to K^0_S pi^0$ decays for both mixing-induced and direct $CP$ violating asymmetry measurements and $B^0 to K^0_L pi^0$ decays for the direct CP violation measurement. The CP violation parameters obtained are $sin 2 phi_1^{rm eff} = +0.67 pm 0.31{(stat)} pm 0.08 {(syst)}$ and $mathcal{A}_{K^0 pi^0} = +0.14 pm 0.13{(stat)} pm 0.06 {(syst)}$. The branching fraction of $B^0 to K^0 pi^0$ decay is measured to be $mathcal{B}(B^0 to K^0 pi^0) = (8.7pm0.5 (rm{stat.})pm0.6 (rm{syst.}))times 10^{-6}$. The observed $mathcal{A}_{K^0 pi^0}$ value differs by 1.9 standard deviations from the value expected from an isospin sum rule.

Search for the lepton-flavor-violating decay $B^{0}to K^{ast 0} mu^{pm} e^{mp}$

We have searched for the lepton-flavor-violating decay $B^{0}to K^{ast 0} mu^{pm} e^{mp}$ using a data sample of 711 $fb^{-1}$ that contains $772 times 10^{6}$ $Bbar{B}$ pairs. The data were collected near the $Upsilon (4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. No signals were observed, and we set 90% confidence level upper limits on the branching fractions of ${cal B}(B^{0}to K^{ast 0} mu^{+} e^{-})< 1.2times 10^{-7}$, ${cal B}(B^{0}to K^{ast 0} mu^{-} e^{+})< 1.6times 10^{-7}$, and, for both decays combined, ${cal B}(B^{0}to K^{ast 0} mu^{pm} e^{mp}) < 1.8times 10^{-7}$. These are the most stringent limits on these decays to date.