ATLAS

Abstract:

This Letter presents a search for tb resonances in 1.04fb-1 of LHC proton-proton collision data collected by the ATLAS detector at a center-of-mass energy of 7 TeV. Events with a lepton, missing transverse momentum, and two jets are selected and the invariant mass of the corresponding final state is reconstructed. The search exploits the shape of the tb invariant mass distribution compared to the expected standard model backgrounds. The model of a right-handed WR′ with standard model-like couplings is chosen as the benchmark model for this search. No statistically significant excess of events is observed in the data, and upper limits on the cross section times the branching ratio of WR′ resonances at 95% C.L. lie in the range of 6.1-1.0 pb for WR′ masses ranging from 0.5 to 2.0 TeV. These limits are translated into a lower bound on the allowed right-handed WR′ mass, giving m WR′>1.13TeV at 95% C.L. © 2012 CERN.

Abstract:

We present a search for the standard model Higgs boson produced in association with a W ± boson. This search uses data corresponding to an integrated luminosity of 7.5fb -1 collected by the CDF detector at the Tevatron. We select WH→νbb̄ candidate events with two jets, large missing transverse energy, and exactly one charged lepton. We further require that at least one jet be identified to originate from a bottom quark. Discrimination between the signal and the large background is achieved through the use of a Bayesian artificial neural network. The number of tagged events and their distributions are consistent with the standard model expectations. We observe no evidence for a Higgs boson signal and set 95% C.L. upper limits on the WH production cross section times the branching ratio to decay to bb̄ pairs, σ(pp̄→W ±H) ×B(H→bb̄), relative to the rate predicted by the standard model. For the Higgs boson mass range of 100 to 150GeV/c2 we set observed (expected) upper limits from 1.34 (1.83) to 38.8 (23.4). For 115GeV/c2 the upper limit is 3.64 (2.78). The combination of the present search with an independent analysis that selects events with three jets yields more stringent limits ranging from 1.12 (1.79) to 34.4 (21.6) in the same mass range. For 115 and 125GeV/c2 the upper limits are 2.65 (2.60) and 4.36 (3.69), respectively. © 2012 American Physical Society.

Abstract:

We report on a study of diffractive dijet production in p̄p collisions at √s=1.96TeV using the CDF II detector at the Fermilab Tevatron p̄p collider. A data sample from 310pb -1 of integrated luminosity collected by triggering on a high transverse energy jet, ETjet, in coincidence with a recoil antiproton detected in a Roman pot spectrometer is used to measure the ratio of single-diffractive to inclusive-dijet event rates as a function of xp ̄ of the interacting parton in the antiproton, the Bjorken-x, xBjp̄, and a Q2(ETjet)2 in the ranges 10 -3-4GeV2. The t p̄ dependence is measured as a function of Q2 and xBjp̄ and compared with that of inclusive single diffraction dissociation. We find weak xBjp̄ and Q2 dependencies in the ratio of single diffractive to inclusive event rates, and no significant Q2 dependence in the diffractive t p̄ distributions. © 2012 American Physical Society.

Abstract:

A search is reported for the pair production of a new quark b′ with at least one b′ decaying to a Z boson and a bottom quark. The data, corresponding to 2.0fb-1 of integrated luminosity, were collected from pp collisions at √s=7TeV with the ATLAS detector at the CERN Large Hadron Collider. Using events with a b-tagged jet and a Z boson reconstructed from opposite-charge electrons, the mass distribution of large transverse momentum b′ candidates is tested for an enhancement. No evidence for a b′ signal is detected in the observed mass distribution, resulting in the exclusion at a 95% confidence level of b′ quarks with masses m b′<400GeV that decay entirely via b′→Z+b. In the case of a vectorlike singlet b′ mixing solely with the third standard model generation, masses mb′<358GeV are excluded. © 2012 CERN.