Measurement of the cross-section for b-jets produced in association with a Z boson at root s=7 TeV with the ATLAS detector ATLAS Collaboration

A measurement is presented of the inclusive cross-section for b-jet production in association with a Z boson in pp collisions at a centre-of-mass energy of root s = 7 TeV. The analysis uses the data sample collected by the ATLAS experiment in 2010, corresponding to an integrated luminosity of approximately 36 pb(-1). The event selection requires a Z boson decaying into high P-T electrons or muons, and at least one b-jet, identified by its displaced vertex, with transverse momentum p(T) > 25 GeV and rapidity vertical bar y vertical bar < 2.1. After subtraction of background processes, the yield is extracted from the vertex mass distribution of the candidate b-jets. The ratio of this cross-section to the inclusive Z cross-section (the average number of b-jets per Z event) is also measured. Both results are found to be in good agreement with perturbative QCD predictions at next-to-leading order

Search for new phenomena in high-mass final states with a photon and a jet from pp collisions at root s=13 TeV with the ATLAS detector

A search is performed for new phenomena in events having a photon with high transverse momentum and a jet collected in 36.7 fb−1 of proton–proton collisions at a centre-of-mass energy of s√ = 13 TeV recorded with the ATLAS detector at the Large Hadron Collider. The invariant mass distribution of the leading photon and jet is examined to look for the resonant production of new particles or the presence of new high-mass states beyond the Standard Model. No significant deviation from the background-only hypothesis is observed and cross-section limits for generic Gaussian-shaped resonances are extracted. Excited quarks hypothesized in quark compositeness models and high-mass states predicted in quantum black hole models with extra dimensions are also examined in the analysis. The observed data exclude, at 95% confidence level, the mass range below 5.3 TeV for excited quarks and 7.1 TeV (4.4 TeV) for quantum black holes in the Arkani-Hamed–Dimopoulos–Dvali (Randall–Sundrum) model with six (one) extra dimensions

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

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

Measurement of the production cross-section of psi(2S) -&gt; J/psi(-&gt; mu(+)mu(-))pi(+) pi(-) in pp collisions at root s=7 TeV at ATLAS

© 2014, The Author(s). Abstract: The prompt and non-prompt production cross-sections for ψ(2S) mesons are measured using 2.1 fb−1 of pp collision data at a centre-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. The measurement exploits the ψ(2S) → J/ψ(→ μ+μ−)π+π− decay mode, and probes ψ(2S) mesons with transverse momenta in the range 10 ≤ pT&lt; 100 GeV and rapidity |y| &lt; 2.0. The results are compared to other measurements of ψ(2S) production at the LHC and to various theoretical models for prompt and non-prompt quarkonium production.[Figure not available: see fulltext.]

Measurement of the production cross-section of ψ(2S) → [J over ψ](→μ[superscript +] μ[superscript −]) π[superscript +] π [superscript −] in pp collisions at √s = 7 TeV at ATLAS

The prompt and non-prompt production cross-sections for ψ(2S) mesons are measured using 2.1 fb[superscript −1] of pp collision data at a centre-of-mass energy of 7 TeV recorded by the ATLAS experiment at the LHC. The measurement exploits the ψ(2S) → [J over ψ](→ μ[superscript +] μ[superscript −])π[superscript +] π[superscript −] decay mode, and probes ψ(2S) mesons with transverse momenta in the range 10 ≤ p[subscript T] < 100 GeV and rapidity |y| < 2.0. The results are compared to other measurements of ψ(2S) production at the LHC and to various theoretical models for prompt and non-prompt quarkonium production.European Organization for Nuclear ResearchUnited States. Dept. of EnergyNational Science Foundation (U.S.)Brookhaven National Laborator

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