We measure the $D^0 - {\bar{D}}^0$ mixing parameters using a time-dependent amplitude analysis of the decay $D^0\to\pi^+\pi^-\pi^0$. The data were recorded with the BABAR detector at center-of-mass ...energies at and near the $\Upsilon(4S)$ resonance, and correspond to an integrated luminosity of approximately 468.1 ${\rm fb}^{-1}$. The neutral $D$ meson candidates are selected from $D^{*}(2010)^+\to D^0 \pi_s^+$ decays where the flavor at the production is identified by the charge of the low momentum pion, $\pi_s^+$. The measured mixing parameters are $x = (1.5\pm1.2\pm0.6) \%$ and $y = (0.2\pm0.9\pm0.5) \%$, where the quoted uncertainties are statistical and systematic, respectively.
We report on the first search for electron-muon lepton flavor violation (LFV) in the decay of a b quark and b antiquark bound state. We look for the LFV decay Υ(3S)→e±μ∓ in a sample of 118 million ...Υ(3S) mesons from 27 fb-1 of data collected with the BABAR detector at the SLAC PEP-II e+e- collider operating with a 10.36 GeV center-of-mass energy. No evidence for a signal is found, and we set a limit on the branching fraction BΥ(3S)→e±μ∓<3.6×10-7 at 90% C. L. This result can be interpreted as a limit ΛNP/gNP2>80 TeV on the energy scale ΛNP divided by the coupling-squared gNP2 of relevant new physics (NP).
We present a search for a neutral, long-lived particle L that is produced in e+e- collisions and decays at a significant distance from the e+e- interaction point into various flavor combinations of ...two oppositely charged tracks. The analysis uses an e+e- data sample with a luminosity of 489.1 fb-1 collected by the BABAR detector at the γ (4S), γ (3S), and γ (2S) resonances and just below the γ (4S). Fitting the two-track mass distribution in search of a signal peak, we do not observe a significant signal, and set 90% confidence level upper limits on the product of the L production cross section, branching fraction, and reconstruction efficiency for six possible two-body L decay modes as a function of the L mass. The efficiency is given for each final state as a function of the mass, lifetime, and transverse momentum of the candidate, allowing application of the upper limits to any production model. In addition, upper limits are provided on the branching fraction B(B→XsL), where Xs is a strange hadronic system.
A study of the two-body decays B^{±}→X_{ccover ¯}K^{±}, where X_{ccover ¯} 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.
Dark sectors charged under a new Abelian interaction have recently received much attention in the context of dark matter models. These models introduce a light new mediator, the so-called dark photon ...(A'), connecting the dark sector to the standard model. We present a search for a dark photon in the reaction e+e-→γA', A'→e+e-, μ+μ- using 514 fb-1 of data collected with the BABAR detector. We observe no statistically significant deviations from the standard model predictions, and we set 90% confidence level upper limits on the mixing strength between the photon and dark photon at the level of10-4-10-3 for dark photon masses in the range 0.02–10.2 GeV We further constrain the range of the parameter space favored by interpretations of the discrepancy between the calculated and measured anomalous magnetic moment of the muon.
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