We describe a measurement of the time-integrated luminosity of the data collected by the BABAR experiment at the PEP-II asymmetric-energy e+e- collider at the Upsilon(4S), Upsilon(3S), and ...Upsilon(2S) resonances and in a continuum region below each resonance. We measure the time-integrated luminosity by counting e+e- --> e+e- and (for the Upsilon(4S) only) e+e- --> mu+mu- candidate events, allowing additional photons in the final state. We use data-corrected simulation to determine the cross sections and reconstruction efficiencies for these processes, as well as the major backgrounds. Due to the large cross sections of e+e- --> e+e- and +e- --> mu+mu-, the statistical uncertainties of the measurement are substantially smaller than the systematic uncertainties. The dominant systematic uncertainties are due to observed differences between data and simulation, as well as uncertainties on the cross sections. For data collected on the Upsilon(3S) and Upsilon(2S) resonances, an additional uncertainty arises due to Upsilon --> e+e- background. For data collected off the Upsilon resonances, we estimate an additional uncertainty due to the time-dependent efficiency variations, which can affect the short off-resonance runs.
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 ϒ(4S) 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.
We study the process $e^+e^-\to J/\psi\pi^{+}\pi^{-}$ with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the BaBar detector at ...center-of-mass energies 10.58 and 10.54 GeV, and correspond to an integrated luminosity of 454 $\mathrm{fb^{-1}}$. We investigate the $J/\psi \pi^{+}\pi^{-}$ mass distribution in the region from 3.5 to 5.5 $\mathrm{GeV/c^{2}}$. Below 3.7 $\mathrm{GeV/c^{2}}$ the $\psi(2S)$ signal dominates, and above 4 $\mathrm{GeV/c^{2}}$ there is a significant peak due to the Y(4260). A fit to the data in the range 3.74 -- 5.50 $\mathrm{GeV/c^{2}}$ yields a mass value $4244 \pm 5$ (stat) $ \pm 4$ (syst)$\mathrm{MeV/c^{2}}$ and a width value $114 ^{+16}_{-15}$ (stat)$ \pm 7$(syst)$\mathrm{MeV}$ for this state. We do not confirm the report from the Belle collaboration of a broad structure at 4.01 $\mathrm{GeV/c^{2}}$. In addition, we investigate the $\pi^{+}\pi^{-}$ system which results from Y(4260) decay.
Based on the full BABAR data sample of 466.5 million BB¯ pairs, we present measurements of the electron spectrum from semileptonic B meson decays. We fit the inclusive electron spectrum to ...distinguish Cabibbo-Kobayashi-Maskawa (CKM) suppressed B→Xueν decays from the CKM-favored B→Xceν decays, and from various other backgrounds, and determine the total semileptonic branching fraction B(B→Xeν)=(10.34±0.04stat±0.26syst)%, averaged over B± and B0 mesons. We determine the spectrum and branching fraction for charmless B→Xueν decays and extract the CKM element |Vub|, by relying on four different QCD calculations based on the heavy quark expansion. While experimentally, the electron momentum region above 2.1 GeV/c is favored, because the background is relatively low, the uncertainties for the theoretical predictions are largest in the region near the kinematic endpoint. Detailed studies to assess the impact of these four predictions on the measurements of the electron spectrum, the branching fraction, and the extraction of the CKM matrix element |Vub| are presented, with the lower limit on the electron momentum varied from 0.8 GeV/c to the kinematic endpoint. We determine |Vub| using each of these different calculations and find, |Vub|=(3.794±0.107exp −0.219 SF+0.292 −0.068 theory+0.078)×10−3 (De Fazio and Neubert), (4.563±0.126exp −0.208 SF+0.230 −0.163 theory+0.162)×10−3 (Bosch, Lange, Neubert, and Paz), (3.959±0.104exp −0.154 SF+0.164 −0.079 theory+0.042)×10−3 (Gambino, Giordano, Ossola, and Uraltsev), (3.848±0.108exp −0.070 theory+0.084)×10−3 (dressed gluon exponentiation), where the stated uncertainties refer to the experimental uncertainties of the partial branching fraction measurement, the shape function parameters, and the theoretical calculations.
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.
We study the processes γγ→KS0K±πℓ and γγ→K+K-π0 using a data sample of 519 fb-1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e+e- collider at center-of-mass ...energies at and near the Υ(nS) (n=2, 3, 4) resonances. We observe ηc decays to both final states and perform Dalitz plot analyses using a model-independent partial wave analysis technique. This allows a model-independent measurement of the mass-dependence of the I=1/2 Kπ S-wave amplitude and phase. A comparison between the present measurement and those from previous experiments indicates similar behavior for the phase up to a mass of 1.5 GeV/c2. In contrast, the amplitudes show very marked differences. The data require the presence of a new a0(1950) resonance with parameters m=1931±14±22 MeV/c2 and Γ=271±22±29 MeV.
The processes e+e−→KS0K±π∓π0 and e+e−→KS0K±π∓η are studied over a continuum of energies from threshold to 4 GeV with the initial-state photon radiation method. Using 454 fb−1 of data collected with ...the BABAR detector at the SLAC PEP-II storage ring, the first measurements of the cross sections for these processes are obtained. The intermediate resonance structures from K*0(Kπ)0, K*(892)±(Kπ)∓, and KS0K±ρ∓ are studied. The J/ψ is observed in all of these channels, and corresponding branching fractions are measured.
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