288 research outputs found

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

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    The jet energy scale 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 = 7TeV 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 {pipe}η{pipe}<4. 5. The jet energy 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 jet energy uncertainty is less than 2. 5 % in the central calorimeter region ({pipe}η{pipe}<0. 8) for jets with 60≀pT<800 GeV, and is maximally 14 % for pT<30 GeV in the most forward region 3. 2≀{pipe}η{pipe}<4. 5. The jet energy 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, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is 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. © 2013 CERN for the benefit of the ATLAS collaboration

    Search for high-mass resonances decaying to dilepton final states in pp collisions at s√=7 TeV with the ATLAS detector

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    The ATLAS detector at the Large Hadron Collider is used to search for high-mass resonances decaying to an electron-positron pair or a muon-antimuon pair. The search is sensitive to heavy neutral Zâ€Č gauge bosons, Randall-Sundrum gravitons, Z * bosons, techni-mesons, Kaluza-Klein Z/Îł bosons, and bosons predicted by Torsion models. Results are presented based on an analysis of pp collisions at a center-of-mass energy of 7 TeV corresponding to an integrated luminosity of 4.9 fb−1 in the e + e − channel and 5.0 fb−1 in the ÎŒ + ÎŒ −channel. A Z â€Č boson with Standard Model-like couplings is excluded at 95 % confidence level for masses below 2.22 TeV. A Randall-Sundrum graviton with coupling k/MPl=0.1 is excluded at 95 % confidence level for masses below 2.16 TeV. Limits on the other models are also presented, including Technicolor and Minimal Zâ€Č Models

    Low-dose tamoxifen treatment in juvenile males has long-term adverse effects on the reproductive system: implications for inducible transgenics

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    The tamoxifen-inducible Cre system is a popular transgenic method for controlling the induction of recombination by Cre at a specific time and in a specific cell type. However, tamoxifen is not an inert inducer of recombination, but an established endocrine disruptor with mixed agonist/antagonist activity acting via endogenous estrogen receptors. Such potentially confounding effects should be controlled for, but >40% of publications that have used tamoxifen to generate conditional knockouts have not reported even the minimum appropriate controls. To highlight the importance of this issue, the present study investigated the long-term impacts of different doses of a single systemic tamoxifen injection on the testis and the wider endocrine system. We found that a single dose of tamoxifen less than 10% of the mean dose used for recombination induction, caused adverse effects to the testis and to the reproductive endocrine system that persisted long-term. These data raise significant concerns about the widespread use of tamoxifen induction of recombination, and highlight the importance of including appropriate controls in all pathophysiological studies using this means of induction

    Measurement of Higgs boson production in the diphoton decay channel in pp collisions at center-of-mass energies of 7 and 8 TeV with the ATLAS detector

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    A measurement of the production processes of the recently discovered Higgs boson is performed in the two-photon final state using 4.5  fb[superscript −1] of proton-proton collisions data at √s=7  TeV and 20.3  fb[superscript −1] at √s=8  TeV collected by the ATLAS detector at the Large Hadron Collider. The number of observed Higgs boson decays to diphotons divided by the corresponding Standard Model prediction, called the signal strength, is found to be ÎŒ=1.17±0.27 at the value of the Higgs boson mass measured by ATLAS, m[subscript H]=125.4  GeV. The analysis is optimized to measure the signal strengths for individual Higgs boson production processes at this value of m[subscript H]. They are found to be ÎŒ[subscript ggF]=1.32±0.38, ÎŒ[subscript VBF]=0.8±0.7, ÎŒ[subscript WH]=1.0±1.6, ÎŒ[subscript ZH]=0.1[superscript +3.7 subscript −0.1], and ÎŒ[subscript t [bar over t] H] =1.6[superscript +2.7 subscript −1.8], for Higgs boson production through gluon fusion, vector-boson fusion, and in association with a W or Z boson or a top-quark pair, respectively. Compared with the previously published ATLAS analysis, the results reported here also benefit from a new energy calibration procedure for photons and the subsequent reduction of the systematic uncertainty on the diphoton mass resolution. No significant deviations from the predictions of the Standard Model are found.European Organization for Nuclear ResearchUnited States. Dept. of EnergyNational Science Foundation (U.S.)Brookhaven National Laborator

    Charged-particle distributions at low transverse momentum in √s=13 13 TeV pp interactions measured with the ATLAS detector at the LHC

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    Measurements of distributions of charged particles produced in proton–proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 ÎŒb −1 ÎŒb−1 . The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators
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