Search for WH production with a light Higgs boson decaying to prompt electron-jets in proton-proton collisions at s\sqrt{s}=7 TeV with the ATLAS detector

A search is performed for WH production with a light Higgs boson decaying to hidden-sector particles resulting in clusters of collimated electrons, known as electron-jets. The search is performed with 2.04 fb-1 of data collected in 2011 with the ATLAS detector at the LHC in proton-proton collisions at $\sqrt{s}$=7 TeV. One event satisfying the signal selection criteria is observed, which is consistent with the expected background rate. Limits on the product of the WH production cross section and the branching ratio of a Higgs boson decaying to prompt electron-jets are calculated as a function of a Higgs boson mass in the range from 100 GeV to 140 GeV.Peer Reviewe

Measurement of W(+/-)Z production in proton-proton collisions at root s=7 TeV with the ATLAS detector

A study of W(+/-)Z production in proton-proton collisions at root s = 7 TeV is presented using data corresponding to an integrated luminosity of 4.6 fb(-1) collected with the ATLAS detector at the Large Hadron Collider in 2011. In total, 317 candidates, with a background expectation of 68 +/- 10 events, are observed in double-leptonic decay final states with electrons, muons and missing transverse momentum. The total cross-section is determined to be sigma(tot)(WZ) = 19.0(-1.3)(+1.4)(stat.) +/- 0.9(syst.) +/- 0.4(lumi.) pb, consistent with the Standard Model expectation of 17.6(-1.0)(+1.1) pb. Limits on anomalous triple gauge boson couplings are derived using the transverse momentum spectrum of Z bosons in the selected events. The cross-section is also presented as a function of Z boson transverse momentum and diboson invariant mass

Search for Dark Matter Candidates and Large Extra Dimensions in Events with a Photon and Missing Transverse Momentum in pp Collision Data at root s=7 TeV with the ATLAS Detector

"Results of a search for new phenomena in events with an energetic photon and large missing transverse momentum in proton-proton collisions at root s = 7 TeV are reported. Data collected by the ATLAS experiment at the LHC corresponding to an integrated luminosity of 4.6 fb(-1) are used. Good agreement is observed between the data and the standard model predictions. The results are translated into exclusion limits on models with large extra spatial dimensions and on pair production of weakly interacting dark matter candidates. DOI: 10.1103\/PhysRevLett.110.011802

Jet mass and substructure of inclusive jets in sqrt(s) = 7 TeV pp collisions with the ATLAS experiment

See paper for full list of authors - 30 pages plus author list (53 pages total), 17 figures, submitted to Journal of High Energy PhysicsRecent studies have highlighted the potential of jet substructure techniques to identify the hadronic decays of boosted heavy particles. These studies all rely upon the assumption that the internal substructure of jets generated by QCD radiation is well understood. In this article, this assumption is tested on an inclusive sample of jets recorded with the ATLAS detector in 2010, which corresponds to 35 pb^-1 of pp collisions delivered by the LHC at sqrt(s) = 7 TeV. In a subsample of events with single pp collisions, measurementes corrected for detector efficiency and resolution are presented with full systematic uncertainties. Jet invariant mass, kt splitting scales and n-subjettiness variables are presented for anti-kt R = 1.0 jets and Cambridge-Aachen R = 1.2 jets. Jet invariant-mass spectra for Cambridge-Aachen R = 1.2 jets after a splitting and filtering procedure are also presented. Leading-order parton-shower Monte Carlo predictions for these variables are found to be broadly in agreement with data. The dependence of mean jet mass on additional pp interactions is also explored

Jet energy measurement with the ATLAS detector in proton-proton collisions at sqrt(s)=7 TeV

The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of √s = 7 TeV corresponding to an integrated luminosity of 38 pb−1. Jets are reconstructed with the anti-kt algorithm with distance parameters R = 0.4 or R = 0.6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT ≥ 20 GeV and pseudorapidities |h| < 4.5. The JES systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The JES uncertainty is less than 2.5% in the central calorimeter region (|h| < 0.8) for jets with 60 ≤ pT < 800 GeV, and is maximally 14% for pT < 30 GeV in the most forward region 3.2 ≤ |h| < 4.5. The uncertainty for additional energy from multiple proton-proton collisions in the same bunch crossing is less than 1.5% per additional collision for jets with pT > 50 GeV after a dedicated correction for this effect. The JES is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon pT, the sum of the transverse momenta of tracks associated to the jet, or a system of low-pT jets recoiling against a high-pT jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, providing an improved jet energy resolution and a reduced flavour dependence of the jet response. The JES systematic uncertainty determined from a combination of in situ techniques are consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-pT jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined