We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type $D^0 → h'^-h^-ℓ'^+ℓ^+$ and $D^0 → h'^-h^+ℓ'^±ℓ^∓$, where $h$ and $h'$ represent ...a $K$ or $π$ meson and $ℓ$ and $ℓ '$ an electron or muon. The analysis is based on $468 fb^{-1}$ of $e^+e^-$ annihilation data collected at or close to the $Υ(4S)$ resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes, and we establish 90% confidence level upper limits on the branching fractions in the range $(1.0 – 30.6) × 10^{-7}$. The limits are between 1 and 3 orders of magnitude more stringent than previous measurements.
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We report the observation of the rare charm decay D0 → K-π+e+e- , based on 468 fb-1 of e+e- annihilation data collected at or close to the center-of-mass energy of the γ ( 4 S ) resonance with the ...BABAR detector at the SLAC National Accelerator Laboratory. We find the branching fraction in the invariant mass range 0.675<m ( e+e- ) <0.875 GeV / c2 of the electron-positron pair to be B ( D0 → K-π+e+e- ) = ( 4.0±0.5±0.2±0.1 ) ×10-6 , where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty in the branching fraction of the decay D0 → K-π+π+π- used as a normalization mode. The significance of the observation corresponds to 9.7 standard deviations including systematic uncertainties. This result is consistent with the recently reported D0 → K-π+μ+μ- branching fraction, measured in the same invariant mass range, and with the value expected in the standard model. In a set of regions of m ( e+e- ) , where long-distance effects are potentially small, we determine a 90% confidence level upper limit on the branching fraction B ( D0 → K-π+e+e- ) <3.1×10-6 .
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We present a search for seven lepton-flavor-violating neutral charm meson decays of the type D 0 → X 0 e ± μ ∓ , where X 0 represents a π 0 , K S0, ¯ K *0, ρ 0 , ϕ , ω , or η meson. The analysis is ...based on 468 fb −1 of e + e − annihilation data collected at or close to the Υ ( 4 S ) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signals are observed, and we establish 90% confidence level upper limits on the branching fractions in the range ( 5.0 − 22.5 ) × 10 −7 . The limits are between 1 and 2 orders of magnitude more stringent than previous measurements.
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A study of the two-body decays B±→Xcc¯K±, where Xcc¯ refers to one charmonium state, is reported by the BABAR Collaboration using a data sample of 424 fb−1. The absolute determination of branching ...fractions for these decays are significantly improved compared to previous BABAR measurements. Evidence is found for the decay B+→X(3872)K+ at the 3σ level. The absolute branching fraction BB+→X(3872)K+=2.1±0.6(stat)±0.3(syst)×10−4 is measured for the first time. It follows that BX(3872)→J/ψπ+π−=(4.1±1.3)%, supporting the hypothesis of a molecular component for this resonance.
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We search for the rare flavor-changing neutral current process $B^- \to \Lambda {\overline p} \nu{\overline{\nu}}$ using data from the B\textsc{a}B\textsc{ar} experiment. A total of 424 fb$^{-1}$ of ...$e^+e^-$ collision data collected at the center-of-mass energy of the $\Upsilon$(4S) resonance is used in this study, corresponding to a sample of ${(471 \pm 3) \times 10^{6}}$ $B\overline{B}$ pairs. Signal $B^- \to \Lambda {\overline p} \nu{\overline{\nu}}$ candidates are identified by first fully reconstructing a $B^+$ decay in one of many possible exclusive decays to hadronic final states, then examining detector activity that is not associated with this reconstructed $B^+$ decay for evidence of a signal $B^- \to \Lambda {\overline p} \nu{\overline{\nu}}$ decay. The data yield is found to be consistent with the expected background contribution under a null signal hypothesis, resulting in an upper limit of ${{\cal B} (B^- \to \Lambda {\overline p} \nu{\overline{\nu}}) < 3.0\times 10^{-5}}$ at the $90\%$ confidence level.
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An angular analysis of the decay $\bar{B}$ → D*ℓ ¯$\bar{ν}_ℓ$, ℓϵ {e,μ}, is reported using the full e+e- collision data set collected by the BABAR experiment at the Υ(4S) resonance. One B meson from ...the Υ(4S) → $B\bar{B}$ decay is fully reconstructed in a hadronic decay mode, which constrains the kinematics and provides a determination of the neutrino momentum vector. The kinematics of the semileptonic decay is described by the dilepton mass squared, q2, and three angles. The first unbinned fit to the full four-dimensional decay rate in the standard model is performed in the so-called Boyd-Grinstein-Lebed approach, which employs a generic q2 parametrization of the underlying form factors based on crossing symmetry, analyticity, and QCD dispersion relations for the amplitudes. A fit using the more model-dependent Caprini-Lellouch-Neubert (CLN) approach is performed as well. Our form factor shapes show deviations from previous fits based on the CLN parametrization. The latest form factors also provide an updated prediction for the branching fraction ratio $\mathscr{R}$(D*) ≡ $\mathscr{B}$($\bar{B}$ → D* τ¯ $\bar{ν}_τ$)/$\mathscr{B}$($\bar{B}$ → D*ℓ¯ $\bar{ν}_ℓ$) = 0.253 ± 0.005 . Finally, using the well-measured branching fraction for the $\bar{B}$ → D*ℓ¯ $\bar{ν}_ℓ$ decay, a value of |Vcb| = (38.36 ± 0.90) × 10⁻3 is obtained that is consistent with the current world average for exclusive $\bar{B}$ → D (*)ℓ⁻$\bar{ν}_ℓ$ decays and remains in tension with the determination from inclusive semileptonic B decays to final states with charm.
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