ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2014). Observation of an Excited B-c(+/-) Meson State with the ATLAS Detector. Phys. Rev. Lett., 113(21), 212004–18pp.
Abstract: A search for excited states of the B-c(+/-) meson is performed using 4.9 fb(-1) of 7 TeV and 19.2 fb(-1) of 8 TeV pp collision data collected by the ATLAS experiment at the LHC. A new state is observed through its hadronic transition to the ground state, with the latter detected in the decayB(c)(+/-) -> J/psi pi(+/-). The state appears in the m(B-c(+/-)pi(+)pi(-)) – m(B-c(+/-)) – 2m(pi(+/-)) mass difference distribution with a significance of 5.2 standard deviations. The mass of the observed state is 6842 +/- 4 +/- 5 MeV, where the first error is statistical and the second is systematic. The mass and decay of this state are consistent with expectations for the second S-wave state of the B-c(+/-) meson, B-c(+/-)(2S).
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Evidence for CP Violation in B+ -> p(p)over-barK(+) Decays. Phys. Rev. Lett., 113(14), 141801–9pp.
Abstract: Three-body B+ -> p (p) over barK(+) and B+ -> p (p) over bar pi(+) decays are studied using a data sample corresponding to an integrated luminosity of 3.0 fb(-1) collected by the LHCb experiment in proton-proton collisions at center-of-mass energies of 7 and 8 TeV. Evidence of CP violation in the B+ -> p (p) over barK(+) decay is found in regions of the phase space, representing the first measurement of this kind for a final state containing baryons. Measurements of the forward-backward asymmetry of the light meson in the p (p) over bar rest frame yield A(FB)(p (p) over barK(+), m(p (p) over bar) < 2.85 GeV/c(2)) = 0.495 +/- 0.012 (stat) +/- 0.007 (syst) and A(FB)(p<(p)over bar>pi(+), m(p (p) over bar) < 2.85 GeV/c(2)) = -0.409 +/- 0.033 (stat) +/- 0.006 (syst). In addition, the branching fraction of the decay B+ -> <(Lambda)over bar>(1520)p is measured to be B(B+ -> (Lambda) over bar (1520)p) = (3.15 +/- 0.48 (stat) +/- 0.07 (syst) +/- 0.26 (BF)) x 10(-7), where BF denotes the uncertainty on secondary branching fractions.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). First Measurement of the Charge Asymmetry in Beauty-Quark Pair Production. Phys. Rev. Lett., 113(8), 082003–9pp.
Abstract: The difference in the angular distributions between beauty quarks and antiquarks, referred to as the charge asymmetry, is measured for the first time in b (b) over bar pair production at a hadron collider. The data used correspond to an integrated luminosity of 1.0 fb(-1) collected at 7 TeV center-of-mass energy in proton-proton collisions with the LHCb detector. The measurement is performed in three regions of the invariant mass of the b (b) over bar system. The results obtained are A(C)(b (b) over bar) (40 < M-b<(b)over bar> < 75 GeV/c(2)) = 0.4 +/- 0.4 +/- 0.3%, A(C)(b (b) over bar) (75 < M-b<(b)over bar> < 105 GeV/c(2)) = 2.0 +/- 0.9 +/- 0.6%, A(C)(b (b) over bar) (M-b (b) over bar > 10(5) GeV/c(2)) = 1.6 +/- 1.7 +/- 0.6%,where A(C)(b (b) over bar) is defined as the asymmetry in the difference in rapidity between jets formed from the beauty quark and antiquark, where in each case the first uncertainty is statistical and the second systematic. The beauty jets are required to satisfy 2 < eta < 4, E-T > 20 GeV, and have an opening angle in the transverse plane Delta phi > 2.6 rad. These measurements are consistent with the predictions of the standard model.
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T2K Collaboration(Abe, K. et al), Cervera-Villanueva, A., Escudero, L., Izmaylov, A., Sorel, M., & Stamoulis, P. (2014). Measurement of the Inclusive Electron Neutrino Charged Current Cross Section on Carbon with the T2K Near Detector. Phys. Rev. Lett., 113(24), 241803–7pp.
Abstract: The T2K off-axis near detector ND280 is used to make the first differential cross-section measurements of electron neutrino charged current interactions at energies similar to 1 GeV as a function of electron momentum, electron scattering angle, and four-momentum transfer of the interaction. The total flux-averaged nu(e) charged current cross section on carbon is measured to be <sigma >(phi) = 1.11 +/- 0.10(stat) +/- 0.18(syst) x 10(-38) cm(2)/nucleon. The differential and total cross- section measurements agree with the predictions of two leading neutrino interaction generators, NEUT and GENIE. The NEUT prediction is 1.23 x 10(-38) cm(2)/nucleon and the GENIE prediction is 1.08 x 10(-38) cm(2)/nucleon. The total nu(e) charged current cross-section result is also in agreement with data from the Gargamelle experiment.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Precision Measurement of the Mass and Lifetime of the Xi(-)(b) Baryon. Phys. Rev. Lett., 113(24), 242002–9pp.
Abstract: We report on measurements of the mass and lifetime of the Xi(-)(b) baryon using about 1800 Xi(-)(b) decays reconstructed in a proton-proton collision data set corresponding to an integrated luminosity of 3.0 fb(-1) collected by the LHCb experiment. The decays are reconstructed in the Xi(-)(b) -> Xi(0)(c)pi(-), Xi(0)(c) -> pK(-)K(-)pi(+) channel and the mass and lifetime are measured using the Lambda(0)(b) -> Lambda(+)(c)pi(-) mode as a reference. We measure M(Xi(-)(b)) – M(Lambda(0)(b)) = 178.36 +/- 0.46 +/- 0.16 MeV/c(2), (tau Xi(-)(b)/tau Lambda(0)(b)) = 1.089 +/- 0.026 +/- 0.011, where the uncertainties are statistical and systematic, respectively. These results lead to a factor of 2 better precision on the Xi(-)(b) mass and lifetime compared to previous best measurements, and are consistent with theoretical expectations.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Observation of Two New Xi(-)(b) Baryon Resonances. Phys. Rev. Lett., 114(6), 062004–9pp.
Abstract: Two structures are observed close to the kinematic threshold in the Xi(0)(b)pi(-) mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), recorded by the LEICb experiment. In the quark model, two baryonic resonances with quark content bds are expected in this mass region: the spin-parity J(P) = (1/2)(+) and J(P) = (3/2)(+) states, denoted Xi'(-)(b) and Xi*(-)(b). Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be m(Xi'(-)(b)) – m(Xi(0)(b)) – m(pi(-))=3.653 +/- 0.018 +/- 0.006 MeV/c(2), m(Xi*(-)(b)) – m(Xi(0)(b)) – m(pi(-)) = 23.96 +/- 0.12 +/- 0.06 MeV/e(2), Gamma(Xi*(-)(b)) = 1.65 +/- 0.31 +/- 0.10 MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of Gamma(Xi'(-)(b)) < 0.08 MeV at 95% confidence level. Relative production rates of these states are also reported.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2015). Measurements of the Nuclear Modification Factor for Jets in Pb plus Pb Collisions at root SNN=2.76 TeV with the ATLAS Detector. Phys. Rev. Lett., 114(7), 072302–18pp.
Abstract: Measurements of inclusive jet production are performed in pp and Pb + Pb collisions at root SNN = 2.76 TeV with the ATLAS detector at the LHC, corresponding to integrated luminosities of 4.0 and 0.14 nb(-1), respectively. The jets are identified with the anti-k(t) algorithm with R = 0.4, and the spectra are measured over the kinematic range of jet transverse momentum 32 < pT < 500 GeV and absolute rapidity |y| < 2.1 and as a function of collision centrality. The nuclear modification factor R-AA is evaluated, and jets are found to be suppressed by approximately a factor of 2 in central collisions compared to pp collisions. The RAA shows a slight increase with pT and no significant variation with rapidity.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Measurement of the Semileptonic CP Asymmetry in B-0-(B)over-bar(0) Mixing. Phys. Rev. Lett., 114(4), 041601–9pp.
Abstract: The semileptonic CP asymmetry in B-0-(B) over bar (0) mixing, a(s1)(d), is measured in proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), recorded by the LHCb experiment. Semileptonic B-0 decays are reconstructed in the inclusive final states D-mu(+) and D*(-)mu(+), where the D- meson decays into the K+pi(-)pi(-) final state and the D*(-) meson into the (D) over bar (0)(-> K+pi(-))pi(-) final state. The asymmetry between the numbers of D-(*()-)mu(+) and D-(*()+)mu(-) decays is measured as a function of the decay time of the B-0 mesons. The CP asymmetry is measured to be a(s1)(d) = (-0.02 +/- 0.19 +/- 0.30)%, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of a(s1)(d) to date and is consistent with the prediction from the standard model.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2015). Study of CP Asymmetry in B-0-(B)over-bar(0) Mixing with Inclusive Dilepton Events. Phys. Rev. Lett., 114(8), 081801–8pp.
Abstract: We present a measurement of the asymmetry A(CP) between same- sign inclusive dilepton samples l(+) l(+) and l(-) l(-) ( l = e, mu) from semileptonic B decays in Y(4S) -> B (B) over bar events, using the complete data set recorded by the BABAR experiment near the Y(4S) resonance, corresponding to 471 x 10(6) B (B) over bar pairs. The asymmetry A(CP) allows comparison between the mixing probabilities P((B) over bar (0) -> B-0) and P(B-0 -> (B) over bar (0)) and therefore probes CP and T violation. The result, A(CP) = [-3.9 +/- 3.5(stat) +/- 1.9(syst)] x 10(-3), is consistent with the standard model expectation.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2015). Search for Higgs Boson Pair Production in the gamma gamma b(b)over-bar Final State Using pp Collision Data at root s=8 TeV from the ATLAS Detector. Phys. Rev. Lett., 114(8), 081802–19pp.
Abstract: Searches are performed for resonant and nonresonant Higgs boson pair production in the gamma gamma b (b) over bar final state using 20 fb(-1) of proton-proton collisions at a center-of-mass energy of 8 TeV recorded with the ATLAS detector at the CERN Large Hadron Collider. A 95% confidence level upper limit on the cross section times branching ratio of nonresonant production is set at 2.2 pb, while the expected limit is 1.0 pb. The difference derives from a modest excess of events, corresponding to 2.4 standard deviations from the background-only hypothesis. The limit observed in the search for a narrow X -> hh resonance ranges between 0.7 and 3.5 pb as a function of the resonance mass.
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