Person:

Morii, Masahiro

We present a study of the decays B±→DK± with D mesons reconstructed in the K+π−π0 or K−π+π0 final states, where D indicates a D0 or a D⎯⎯⎯0 meson. Using a sample of 474×106 BB⎯⎯⎯ pairs collected with the BABAR detector at the PEP-II asymmetric-energy e+e− collider at SLAC, we measure the ratios R±≡Γ(B±→[K∓π±π0]DK±)Γ(B±→[K±π∓π0]DK±). We obtain R+=(5+12−10(stat)+2−4(syst))×10−3 and R−=(12+12−10(stat)+3−5(syst))×10−3, from which we extract the upper limits at 90% probability: R+<23×10−3 and R−<29×10−3. Using these measurements, we obtain an upper limit for the ratio rB of the magnitudes of the b→u and b→c amplitudes rB<0.13 at 90% probability.

We study the processes γγ→K0SK±π∓ and γγ→K+K−π+π−π0 using a data sample of 519.2fb−1 recorded by the BABAR detector at the PEP-II asymmetric-energy e+e− collider at center-of-mass energies near the Υ(nS) (n=2, 3, 4) resonances. We observe the ηc(1S), χc0(1P) and ηc(2S) resonances produced in two-photon interactions and decaying to K+K−π+π−π0, with significances of 18.1, 5.4 and 5.3 standard deviations (including systematic errors), respectively, and report 4.0σ evidence of the χc2(1P) decay to this final state. We measure the ηc(2S) mass and width in K0SK±π∓ decays, and obtain the values m(ηc(2S))=3638.5±1.5±0.8  MeV/c2 and Γ(ηc(2S))=13.4±4.6±3.2  MeV, where the first uncertainty is statistical and the second is systematic. We measure the two-photon width times branching fraction for the reported resonance signals, and search for the χc2(2P) resonance, but no significant signal is observed.

We search for single-photon decays of the (Υ(1S)) resonance, (Υ→γ+) invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson (A^0), or a pair of dark matter particles, (χ\overline{χ}). Both (A^0) and χ are assumed to have zero spin. We tag (Υ(1S)) decays with a dipion transition (Υ(2S)→π^{+}π^{−}Υ(1S)) and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range (m_{A^{0}}≤9.2 GeV) and (m_{χ}≤4.5 GeV) in the sample of (98×10^{6} Υ(2S)) decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states.

The production of W boson pairs in proton-proton collisions at √s = 8 TeV is studied using data corresponding to 20.3 fb−1 of integrated luminosity collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The W bosons are reconstructed using their leptonic decays into electrons or muons and neutrinos. Events with reconstructed jets are not included in the candidate event sample. A total of 6636 WW candidate events are observed. Measurements are performed in fiducial regions closely approximating the detector acceptance. The integrated measurement is corrected for all acceptance effects and for the W branching fractions to leptons in order to obtain the total WW production cross section, which is found to be 71.1±1.1(stat) +5.7−5.0 (syst) ±1.4(lumi) pb. This agrees with the next-tonext-to-leading-order Standard Model prediction of 63.2+1.6−1.4 (scale)±1.2(PDF) pb. Fiducial differential cross sections are measured as a function of each of six kinematic variables. The distribution of the transverse momentum of the leading lepton is used to set limits on anomalous triple-gauge-boson couplings.

We report on analyses of tau lepton decays (τ^{−}→ηK^{−}ν_{τ}) and (τ^{−}→ηπ^{−}ν_{τ}), with (η→π^{+}π^{−}π^{0}), using (470 fb^{−1}) of data from the BABAR experiment at PEP-II, collected at center-of-mass energies at and near the (Υ(4S)) resonance. We measure the branching fraction for the (τ^{−}→ηK^{−}ν_{τ}) decay mode, (ℬ(τ^{−}→ηK^{−}ν_{τ})=(1.42±0.11(stat)±0.07(syst))×10^{−4}), and report a 95% confidence level upper limit for the second-class current process (τ^{−}→ηπ^{−}ν_{τ}), (ℬ(τ^{−}→ηπ^{−}ν_{τ})<9.9×10^{−5}).

We present an analysis of exclusive charmless semileptonic B-meson decays based on (377×10^{6} B\overline{B}) pairs recorded with the BABAR detector at the (Υ(4S)) resonance. We select four event samples corresponding to the decay modes (B^{0}→π^{−}ℓ^{+}ν), (B^{+}→π^{0}ℓ^{+}ν), (B^{0}→ρ^{−}ℓ^{+}ν), and (B^{+}→ρ^{0}ℓ^{+}ν) and find the measured branching fractions to be consistent with isospin symmetry. Assuming isospin symmetry, we combine the two (B→πℓν) samples, and similarly the two (B→ρℓν) samples, and measure the branching fractions (ℬ(B^{0}→π^{−}ℓ^{+}ν)=(1.41±0.05±0.07)×10^{−4}) and (ℬ(B^{0}→ρ^{−}ℓ^{+}ν)=(1.75±0.15±0.27)×10^{−4}), where the errors are statistical and systematic. We compare the measured distribution in (q^2), the momentum transfer squared, with predictions for the form factors from QCD calculations and determine the Cabibbo-Kobayashi-Maskawa matrix element (|V_{ub}|). Based on the measured partial branching fraction for (B→πℓν) in the range (q^{2}<12 GeV^{2}) and the most recent QCD light-cone sum-rule calculations, we obtain (|V_{ub}|=(3.78±0.13^{+0.55}{−0.40})×10^{−3}), where the errors refer to the experimental and theoretical uncertainties. From a simultaneous fit to the data over the full (q^2) range and the FNAL/MILC lattice QCD results, we obtain (|V{ub}|=(2.95±0.31)×10^{−3}) from (B→πℓν), where the error is the combined experimental and theoretical uncertainty.