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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). First Observation of a Baryonic B-c(+) Decay. Phys. Rev. Lett., 113(15), 152003–9pp.
Abstract: A baryonic decay of the B-c(+) meson, B-c(+) -> J/psi p (p) over bar pi(+) is observed for the first time, with a significance of 7.3 standard deviations, in pp collision data collected with the LHCb detector and corresponding to an integrated luminosity of 3.0 fb(-1) taken at center-of-mass energies of 7 and 8 TeV. With the B-c(+) -> J/psi pi(+) decay as the normalization channel, the ratio of branching fractions is measured to be B(B-c(+) -> J/psi p (p) over bar pi(+)) /B(B-c(+) -> J/psi pi(+)) = 0.143(-0.034)(+0.039) (stat) +/- 0.013 (syst). The mass of the B-c(+) messon is determined as M(B-c(+)) = 6274.0 +/- 0.4 (sysst) MeV/c(2), using the B-c(+) -> J/psi p (p) over bar pi(+) channel.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Test of lepton universality using B+ -> K(+)l(+)l(-) decays. Phys. Rev. Lett., 113(15), 151601–10pp.
Abstract: A measurement of the ratio of the branching fractions of the B+ -> K+mu(+)mu(-) and B+ -> K(+)e(+)e(-) decays is presented using proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb(-1), recorded with the LHCb experiment at center-of-mass energies of 7 and 8 TeV. The value of the ratio of branching fractions for the dilepton invariant mass squared range 1 < q(2) < 6 GeV2/c(4) is measured to be 0.745(-0.074)(+0.090)(stat) +/- 0.036(syst). This value is the most precise measurement of the ratio of branching fractions to date and is compatible with the standard model prediction within 2.6 standard deviations.
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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. (2014). Evidence for Electroweak Production of W(+/-) W(+/-) jj in pp Collisions at root s=8 TeV with the ATLAS Detector. Phys. Rev. Lett., 113(14), 141803–19pp.
Abstract: This Letter presents the first study of W(+/-)W(+/-)jj, same-electric-charge diboson production in association with two jets, using 20.3 fb(-1) of proton-proton collision data at root s = 8 TeV recorded by the ATLAS detector at the Large Hadron Collider. Events with two reconstructed same-charge leptons (e(+/-)e(+/-), e(+/-)mu(+/-), and mu(+/-)mu(+/-)) and two or more jets are analyzed. Production cross sections are measured in two fiducial regions, with different sensitivities to the electroweak and strong production mechanisms. First evidence for W(+/-)W(+/-)jj production and electroweak-only W(+/-)W(+/-)jj production is observed with a significance of 4.5 and 3.6 standard deviations, respectively. The measured production cross sections are in agreement with standard model predictions. Limits at 95% confidence level are set on anomalous quartic gauge couplings.
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., Oyanguren, A., & Villanueva-Perez, P. (2014). Search for a Dark Photon in e(+)e(-) Collisions at BABAR. Phys. Rev. Lett., 113(20), 201801–8pp.
Abstract: 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(-) ->gamma A', A' -> e(+)e(-), mu(+) mu(-) 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 of 10(-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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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2014). Measurement of the CP-Violating Phase phi(s) in (B)over-bar(s)(0) -> Ds+Ds- Decays. Phys. Rev. Lett., 113(21), 211801–9pp.
Abstract: We present a measurement of the CP-violating weak mixing phase phi(s) using the decay (B) over bar (0)(s) -> Ds+Ds- in a data sample corresponding to 3.0 fb(-1) of integrated luminosity collected with the LHCb detector in pp collisions at center-of-mass energies of 7 and 8 TeV. An analysis of the time evolution of the system, which does not use the constraint vertical bar lambda vertical bar = 1 to allow for the presence of CP violation in decay, yields phi(s) = 0.02 +/- 0.17(stat) +/- 0.02(syst) rad, vertical bar lambda vertical bar = 0.91(-0.15)(+0.18)(stat) +/- 0.02(syst). This result 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., 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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