A measurement of the correlations between the polar angles of leptons from the decay of pair-produced t and t¯ quarks in the helicity basis is reported, using proton-proton collision data collected by the ATLAS d...
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A measurement of the correlations between the polar angles of leptons from the decay of pair-produced t and t¯ quarks in the helicity basis is reported, using proton-proton collision data collected by the ATLAS detector at the LHC. The dataset corresponds to an integrated luminosity of 4.6 fb−1 at a center-of-mass energy of s=7 TeV collected during 2011. Candidate events are selected in the dilepton topology with large missing transverse momentum and at least two jets. The angles θ1 and θ2 between the charged leptons and the direction of motion of the parent quarks in the tt¯ rest frame are sensitive to the spin information, and the distribution of cosθ1·cosθ2 is sensitive to the spin correlation between the t and t¯ quarks. The distribution is unfolded to parton level and compared to the next-to-leading order prediction. A good agreement is observed.
This paper presents a study of and triboson production using events from proton-proton collisions at a centre-of-mass energy of recorded with the ATLAS detector at the LHC and corresponding to an integrated luminos...
This paper presents a study of and triboson production using events from proton-proton collisions at a centre-of-mass energy of recorded with the ATLAS detector at the LHC and corresponding to an integrated luminosity of 20.2 fb . The production cross-section is determined using a final state containing an electron, a muon, a photon, and neutrinos ( ). Upper limits on the production cross-section of the final state and the and final states containing an electron or a muon, two jets, a photon, and a neutrino ( or ) are also derived. The results are compared to the cross-sections predicted by the Standard Model at next-to-leading order in the strong-coupling constant. In addition, upper limits on the production cross-sections are derived in a fiducial region optimised for a search for new physics beyond the Standard Model. The results are interpreted in the context of anomalous quartic gauge couplings using an effective field theory. Confidence intervals at 95% confidence level are derived for the 14 coupling coefficients to which and production are sensitive.
A search for highly ionizing particles produced in proton-proton collisions at 8 TeV center-of-mass energy is performed by the ATLAS Collaboration at the CERN Large Hadron Collider. The data set used corresponds to an...
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A search for highly ionizing particles produced in proton-proton collisions at 8 TeV center-of-mass energy is performed by the ATLAS Collaboration at the CERN Large Hadron Collider. The data set used corresponds to an integrated luminosity of 7.0 fb−1. A customized trigger significantly increases the sensitivity, permitting a search for such particles with charges and energies beyond what was previously accessible. No events were found in the signal region, leading to production cross section upper limits in the mass range 200–2500 GeV for magnetic monopoles with magnetic charge in the range 0.5gD<|g|<2.0gD, where gD is the Dirac charge, and for stable particles with electric charge in the range 10<|z|<60. Model-dependent limits are presented in given pair-production scenarios, and model-independent limits are presented in fiducial regions of particle energy and pseudorapidity.
Communications networks are valuable in proportion to the trustworthy information they carry. Network security policies are designed to classify nodes as trustworthy or not with some probability of error when the true...
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Communications networks are valuable in proportion to the trustworthy information they carry. Network security policies are designed to classify nodes as trustworthy or not with some probability of error when the true status of each node is unknown. By making an analogy with the binary symmetric channel model, properties of networks with optimal security policies are derived. Additive and multiplicative utility models with and without aversion to misclassification risk are considered.
The momentum-weighted sum of the charges of tracks associated to a jet is sensitive to the charge of the initiating quark or gluon. This paper presents a measurement of the distribution of momentum-weighted sums, call...
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The momentum-weighted sum of the charges of tracks associated to a jet is sensitive to the charge of the initiating quark or gluon. This paper presents a measurement of the distribution of momentum-weighted sums, called jet charge, in dijet events using 20.3 fb−1 of data recorded with the ATLAS detector at s=8 TeV in pp collisions at the LHC. The jet charge distribution is unfolded to remove distortions from detector effects and the resulting particle-level distribution is compared with several models. The pT dependence of the jet charge distribution average and standard deviation are compared to predictions obtained with several leading-order and next-to-leading-order parton distribution functions. The data are also compared to different Monte Carlo simulations of QCD dijet production using various settings of the free parameters within these models. The chosen value of the strong coupling constant used to calculate gluon radiation is found to have a significant impact on the predicted jet charge. There is evidence for a pT dependence of the jet charge distribution for a given jet flavor. In agreement with perturbative QCD predictions, the data show that the average jet charge of quark-initiated jets decreases in magnitude as the energy of the jet increases.
Prompt photon production in sNN=2.76-TeV Pb+Pb collisions has been measured by the ATLAS experiment at the Large Hadron Collider using data collected in 2011 with an integrated luminosity of 0.14 nb−1. Inclusive photo...
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Prompt photon production in sNN=2.76-TeV Pb+Pb collisions has been measured by the ATLAS experiment at the Large Hadron Collider using data collected in 2011 with an integrated luminosity of 0.14 nb−1. Inclusive photon yields, scaled by the mean nuclear thickness function, are presented as a function of collision centrality and transverse momentum in two pseudorapidity intervals, |η|<1.37 and 1.52≤|η|<2.37. The scaled yields in the two pseudorapidity intervals, as well as the ratios of the forward yields to those at midrapidity, are compared to the expectations from next-to-leading-order perturbative QCD (pQCD) calculations. The measured cross sections agree well with the predictions for proton-proton collisions within statistical and systematic uncertainties. Both the yields and the ratios are also compared to two other pQCD calculations, one which uses the isospin content appropriate to colliding lead nuclei and another which includes nuclear modifications to the nucleon parton distribution functions.
In this paper, the metal-semiconductor-metal (MSM) Schottky AlN photodetectors (PDs) on Si substrates show a dark current as low as ~1 nA at a bias up to 200 V. Excellent thermal stability and radiation hardness of so...
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In this paper, the metal-semiconductor-metal (MSM) Schottky AlN photodetectors (PDs) on Si substrates show a dark current as low as ~1 nA at a bias up to 200 V. Excellent thermal stability and radiation hardness of solar-blind AlN MSM PDs are achieved. The working temperature is up to 300 °C and the radiation tolerance is up to 10 13 cm -2 of 2 MeV proton fluences for AlN MSM PDs. The results demonstrate the high promise of AlN as an active material for solar-blind DUV photodetection in extremely harsh environments.
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