BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2015). Observation of the baryonic decay (B)over-bar(0) -> Lambda(+)(c)(p)over-barK(-)K(+). Phys. Rev. D, 91(3), 031102–7pp.
Abstract: We report the observation of the baryonic decay (B) over bar (0) -> Lambda(+)(c)(p) over barK(-)K(+) using a data sample of 471 x 10(6) B (B) over bar pairs produced in e(+)e(-) annihilations at root s = 10.58 GeV. This data sample was recorded with the BABAR detector at the PEP- II storage ring at SLAC. We find B((B) over bar (0) -> Lambda(+)(c)(p) over barK(-)K(+)) = (2.5 +/- 0.4((stat)) +/- 0.2((syst)) +/- 0.6(B(Lambda c+)) ) x 10(-5) where the uncertainties are statistical, systematic, and due to the uncertainty of the Lambda(+)(c) -> (p) over barK(-)pi(+) branching fraction, respectively. The result has a significance corresponding to 5.0 standard deviations, including all uncertainties. For the resonant decay (B) over bar (0) -> Lambda(+)(c)(p) over bar phi, we determine the upper limit B((B) over bar (0) -> Lambda(+)(c)(p) over bar phi) < 1.2 x 10(-5) at 90% confidence level.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Observation and measurement of Higgs boson decays to WW* with the ATLAS detector. Phys. Rev. D, 92(1), 012006–84pp.
Abstract: We report the observation of Higgs boson decays to WW* based on an excess over background of 6.1 standard deviations in the dilepton final state, where the Standard Model expectation is 5.8 standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of 3.2 standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of 25 fb(-1) from root s = 7 and 8 TeV pp collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of 125.36 GeV, the ratio of the measured value to the expected value of the total production cross section times branching fraction is 1.09(-0.15)(+0.16)(stat)(-0.14)(+0.17)(syst). The corresponding ratios for the gluon fusion and vector-boson fusion production mechanisms are 1.02 +/- 0.19(stat)(-0.18)(+0.22)(syst) and 1.27(-0.40)(+0.44)(stat)(-0.21)(+0.30)(syst), respectively. At root s = 8 TeV, the total production cross sections are measured to be sigma(gg -> H -> WW*) = 4.6 +/- 0.9(stat)(-0.7)(+0.8)(syst) pb and sigma(VBF H -> WW*) = 0.51(-0.15)(+0.17)(stat)(-0.08)(+0.13)(syst) pb. The fiducial cross section is determined for the gluon-fusion process in exclusive final states with zero or one associated jet.
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NEXT Collaboration(Serra, L. et al), Sorel, M., Alvarez, V., Carcel, S., Cervera-Villanueva, A., Diaz, J., et al. (2015). An improved measurement of electron-ion recombination in high-pressure xenon gas. J. Instrum., 10, P03025–21pp.
Abstract: We report on results obtained with the NEXT-DEMO prototype of the NEXT-100 high-pressure xenon gas time projection chamber (TPC), filled with pure xenon gas at 10 bar pressure and exposed to an alpha decay calibration source. Compared to our previous measurements with alpha particles, an upgraded detector and improved analysis techniques have been used. We measure event-by-event correlated fluctuations between ionization and scintillation due to electronion recombination in the gas, with correlation coefficients between -0.80 and -0.56 depending on the drift field conditions. By combining the two signals, we obtain a 2.8% FWHM energy resolution for 5.49 MeV alpha particles and a measurement of the optical gain of the electroluminescent TPC. The improved energy resolution also allows us to measure the specific activity of the radon in the gas due to natural impurities. Finally, we measure the average ratio of excited to ionized atoms produced in the xenon gas by alpha particles to be 0.561 +/- 0.045, translating into an average energy to produce a primary scintillation photon of W-ex = (39.2 +/- 3.2) eV.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2015). Measurements of neutrino oscillation in appearance and disappearance channels by the T2K experiment with 6.6 x 10(20) protons on target. Phys. Rev. D, 91(7), 072010–50pp.
Abstract: We report on measurements of neutrino oscillation using data from the T2K long-baseline neutrino experiment collected between 2010 and 2013. In an analysis of muon neutrino disappearance alone, we find the following estimates and 68% confidence intervals for the two possible mass hierarchies: normal hierarchy: sin(2)theta(23) = 0.514(-0.055)(+0.056) and Delta m(32)(2) = (2.51 +/- 0.10) x 10(-3) eV(2)/c(4) and inverted hierarchy: sin(2)theta(23) = 0.511 +/- 0.055 and Delta m(13)(2) = (2.48 +/- 0.10) x 10(-3) eV(2)/c(4). The analysis accounts for multinucleon mechanisms in neutrino interactions which were found to introduce negligible bias. We describe our first analyses that combine measurements of muon neutrino disappearance and electron neutrino appearance to estimate four oscillation parameters, vertical bar Delta m(2)vertical bar, sin(2)theta(23), sin(2)theta(13,) delta(CP), and the mass hierarchy. Frequentist and Bayesian intervals are presented for combinations of these parameters, with and without including recent reactor measurements. At 90% confidence level and including reactor measurements, we exclude the region delta(CP) = [0.15; 0.83]pi for normal hierarchy and delta(CP) = [-0.08; 1.09]pi for inverted hierarchy. The T2K and reactor data weakly favor the normal hierarchy with a Bayes factor of 2.2. The most probable values and 68% one-dimensional credible intervals for the other oscillation parameters, when reactor data are included, are sin(2)theta(23) = 0.528(-0.055)(+0.038) and vertical bar Delta m(32)(2)vertical bar = (2.51 +/- 0.11) x 10(-3) eV(2)/c(4).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Study of B- -> DK-pi(+)pi(-) and B- -> D pi(-)pi(+)pi(-) decays and determination of the CKM angle gamma. Phys. Rev. D, 92(11), 112005–20pp.
Abstract: We report a study of the suppressed B- -> DK-pi(+)pi(-) and favored B- -> D pi(-)pi(+)pi(-) decays, where the neutral D meson is detected through its decays to the K--/+pi(+/-) and CP -even K+K- and pi(+)pi(-) final states. The measurement is carried out using a proton-proton collision data sample collected by the LHCb experiment, corresponding to an integrated luminosity of 3.0 fb(-1). We observe the first significant signals in the CP – even final states of the D meson for both the suppressed B- -> DK-pi(+)pi(-) and favored B- -> D pi(-)pi(+)pi(-) modes, as well as in the doubly Cabibbo suppressed D -> K+pi(-) final state of the B- -> D pi(-)pi(+)pi(-) decay. Evidence for the suppressed decay B- -> DK-pi(+)pi(-), with D -> K+pi(-), is also presented. From the observed yields in the B- -> DK-pi(+)pi(-), B- -> D pi(-)pi(+)pi(-) and their charge conjugate decay modes, the most probable value of the weak phase gamma corresponds to gamma = (74(-19)(+20))degrees. This is one of the most precise single-measurement determinations of gamma to date.
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