LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Search for the Lambda(0)(b) -> Lambda eta ' and Lambda(0)(b) -> Lambda eta decays with the LHCb detector. J. High Energy Phys., 09(9), 006–21pp.
Abstract: A search is performed for the as yet unobserved baryonic Lambda(0)(b) -> Lambda eta' and Lambda(0)(b) -> Lambda eta decays with 3 fb(-1) of proton-proton collision data recorded by the LHCb experiment. The B-0 -> K-s(0)eta' decay is used as a normalisation channel. No significant signal is observed for the Lambda(0)(b) -> Lambda eta' decay. An upper limit is found on the branching fraction of B(Lambda(0)(b) -> Lambda eta') < 3.1 x 10(-6) at 90% confidence level. Evidence is seen for the presence of the Lambda(0)(b) -> Lambda eta 0 decay at the level of 3 sigma significance, with a branching fraction B(Lambda(0)(b) -> Lambda eta) = (9.3(-5.3)(+7.3)) x 10(-6).
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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). Observation of top-quark pair production in association with a photon and measurement of the t(t)over-bar gamma production cross section in pp collisions at root s=7 TeV using the ATLAS detector. Phys. Rev. D, 91(7), 072007–28pp.
Abstract: A search is performed for top-quark pairs (t (t) over bar) produced together with a photon (gamma) with transverse energy greater than 20 GeV using a sample of t (t) over bar candidate events in final states with jets, missing transverse momentum, and one isolated electron or muon. The data set used corresponds to an integrated luminosity of 4.59 fb(-1) of proton-proton collisions at a center-of-mass energy of 7 TeV recorded by the ATLAS detector at the CERN Large Hadron Collider. In total, 140 and 222 t (t) over bar gamma candidate events are observed in the electron and muon channels, to be compared to the expectation of 79 +/- 26 and 120 +/- 39 non-t (t) over bar gamma background events, respectively. The production of t (t) over bar gamma events is observed with a significance of 5.3 standard deviations away from the null hypothesis. The t (t) over bar gamma production cross section times the branching ratio (BR) of the single-lepton decay channel is measured in a fiducial kinematic region within the ATLAS acceptance. The measured value is sigma(fid)(t (t) over bar gamma) x BR = 63 +/- 8(stat)(-13)(+17) (syst) +/- 1(lumi) fb per lepton flavor, in good agreement with the leading-order theoretical calculation normalized to the next-to-leading-order theoretical prediction of 48 +/- 10 fb.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Search for Hidden-Sector Bosons in B-0 -> K*(0)mu(+)mu(-) Decays. Phys. Rev. Lett., 115(16), 161802–10pp.
Abstract: A search is presented for hidden-sector bosons, chi, produced in the decay B-0 -> K*(892)(0)chi, with K*(892)(0) -> K+pi(-) and chi -> mu(+)mu(-). The search is performed using pp-collision data corresponding to 3.0 fb(-1) collected with the LHCb detector. No significant signal is observed in the accessible mass range 214 <= m(chi) <= 4350 MeV, and upper limits are placed on the branching fraction product B(B-0 -> K*(892)(0)chi) X B(chi -> mu(+)mu(-)) as a function of the mass and lifetime of the chi boson. These limits are of the order of 10(-9) for chi lifetimes less than 100 ps over most of the m(chi) range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.
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LHCb Collaboration(Aaij, R. et al), Martinez-Vidal, F., Oyanguren, A., Ruiz Valls, P., & Sanchez Mayordomo, C. (2015). Search for long-lived particles decaying to jet pairs. Eur. Phys. J. C, 75(4), 152–12pp.
Abstract: A search is presented for long-lived particles with a mass between 25 and 50 GeV/c(2) and a lifetime between 1 and 200 ps in a sample of proton-proton collisions at a centre-of-mass energy of root s = 7 TeV, corresponding to an integrated luminosity of 0.62 fb(-1), collected by the LHCb detector. The particles are assumed to be pair-produced by the decay of a standard model-like Higgs boson. The experimental signature of the long-lived particle is a displaced vertex with two associated jets. No excess above the background is observed and limits are set on the production cross-section as a function of the long-lived particle mass and lifetime.
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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). Search for production of WW/WZ resonances decaying to a lepton, neutrino and jets in pp collisions at root s=8 TeV with the ATLAS detector. Eur. Phys. J. C, 75(5), 209–20pp.
Abstract: A search is presented for narrow diboson resonances decaying to WW or WZ in the final state where one W boson decays leptonically (to an electron or a muon plus a neutrino) and the other W/Z boson decays hadronically. The analysis is performed using an integrated luminosity of 20.3 fb(-1) of pp collisions at root s = 8 TeV collected by the ATLAS detector at the large hadron collider. No evidence for resonant diboson production is observed, and resonance masses below 700 and 1490 GeV are excluded at 95 % confidence level for the spin-2 Randall-Sundrum bulk graviton G* with coupling constant of 1.0 and the extended gauge model W' boson respectively.
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