Results are presented of a search for supersymmetric particles in events with large missing transverse momentum and at least one heavy flavour jet candidate in sqrt{s} = 7 TeV proton-proton ...collisions. In a data sample corresponding to an integrated luminosity of 35 pb-1 recorded by the ATLAS experiment at the Large Hadron Collider, no significant excess is observed with respect to the prediction for Standard Model processes. For R-parity conserving models in which sbottoms (stops) are the only squarks to appear in the gluino decay cascade, gluino masses below 590 GeV (520 GeV) are excluded at the 95% C.L. The results are also interpreted in an MSUGRA/CMSSM supersymmetry breaking scenario with tan(beta)=40 and in an SO(10) model framework.
This Letter reports a measurement of the muon charge asymmetry from W bosons produced in proton-proton collisions at a centre-of-mass energy of 7 TeV with the ATLAS experiment at the LHC. The ...asymmetry is measured in the W→μν decay mode as a function of the muon pseudorapidity using a data sample corresponding to a total integrated luminosity of 31 pb−1. The results are compared to predictions based on next-to-leading order calculations with various parton distribution functions. This measurement provides information on the u and d quark momentum fractions in the proton.
A search for squarks and gluinos in final states containing jets, missing transverse momentum and no electrons or muons is presented. The data were recorded by the ATLAS experiment in sqrt(s) = 7 TeV ...proton-proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 35 inverse picobarns of analysed data. Gluino masses below 500 GeV are excluded at the 95% confidence level in simplified models containing only squarks of the first two generations, a gluino octet and a massless neutralino. The exclusion increases to 870 GeV for equal mass squarks and gluinos. In MSUGRA/CMSSM models with tan(beta)= 3, A_0=0 and mu>0, squarks and gluinos of equal mass are excluded below 775 GeV. These are the most stringent limits to date.
We present studies of W and Z bosons with associated high energy photons produced in pp collisions at sqrt(s)=7 TeV. The analysis uses 35 pb-1 of data collected by the ATLAS experiment in 2010. The ...event selection requires W and Z bosons decaying into high pT leptons (electrons or muons) and a photon with ET>15 GeV separated from the lepton(s) by a distance Delta_R(l,gamma)>0.7 in eta-phi space. A total of 95 (97) pp->e nu gamma + X (pp->mu nu gamma + X) and 25 (23) pp->e+ e- gamma + X (pp->mu+ mu- gamma + X) event candidates are selected. The kinematic distributions of the leptons and photons and the production cross sections are measured. The data are found to agree with Standard Model predictions that include next-to-leading-order O(alpha alpha_s) contributions.
A search for new interactions and resonances produced in LHC proton-proton (pp) collisions at a centre-of-mass energy sqrt(s)= 7 TeV has been performed with the ATLAS detector. Using a data set with ...an integrated luminosity of 36 pb-1 dijet mass and angular distributions have been measured up to dijet masses of \sim 3.5 TeV and found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% C.L. on various models for new physics: an excited quark is excluded with mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and Randall-Meade quantum black holes are excluded in models with six extra space-time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. Analysis of the dijet angular distribution using a novel technique 18 simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale {\Lambda} below 9.5 TeV.
A search is presented for new particles in an extension to the Standard Model that includes a heavy Higgs boson H0, an intermediate charged Higgs boson pair H+-, and a light Higgs boson h0. The ...analysis searches for events involving the production of a single heavy neutral Higgs boson which decays to the charged Higgs boson and a W boson, where the charged Higgs boson subsequently decays into a W boson and the lightest neutral Higgs boson decaying to a bottom--antibottom-quark pair. Such a cascade results in a W-boson pair and a bottom--antibottom-quark pair in the final state. Events with exactly one lepton, missing transverse momentum, and at least four jets are selected from a data sample corresponding to an integrated luminosity of 20.3/fb, collected by the ATLAS detector in proton--proton collisions at sort(s)=8 TeV at the LHC. The data are found to be consistent with Standard Model predictions, and 95% confidence-level upper limits are set on the product of cross section and branching ratio. These limits range from 0.065 pb to 43 pb as a function of H0 and H+- masses, with m(h0) fixed at 125 GeV.
A measurement of the cross section for the production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The results are based on an integrated ...luminosity of 4.6 fb-1 collected with the ATLAS detector at the LHC. The cross section is measured as a function of photon pseudorapidity and transverse energy in the kinematic range between 100 GeV and 1000 GeV and in the regions of pseudorapidity less than 1.37 and between 1.52 and 2.37. The results are compared to leading-order parton-shower Monte Carlo models and next-to-leading-order perturbative QCD calculations. Next-to-leading-order perturbative QCD calculations agree well with the measured cross sections as a function of transverse energy and pseudorapidity.
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