103 research outputs found
Recommended from our members
Study of jet shapes in inclusive jet production in pp collisions at √s=7TeV using the ATLAS detector
Jet shapes have been measured in inclusive jet production in proton-proton collisions at √s=7TeV using 3pb-1 of data recorded by the ATLAS experiment at the LHC. Jets are reconstructed using the anti-kt algorithm with transverse momentum 30GeV</p
Recommended from our members
Search for B -L R-parity-violating top squarks in vs=13 TeV pp collisions with the ATLAS experiment
A search is presented for the direct pair production of the stop, the supersymmetric partner of the top quark, that decays through an R-parity-violating coupling to a final state with two leptons and two jets, at least one of which is identified as a b-jet. The data set corresponds to an integrated luminosity of 36.1 fb-1 of proton-proton collisions at a center-of-mass energy of vs=13 TeV, collected in 2015 and 2016 by the ATLAS detector at the LHC. No significant excess is observed over the Standard Model background, and exclusion limits are set on stop pair production at a 95% confidence level. Lower limits on the stop mass are set between 600 GeV and 1.5 TeV for branching ratios above 10% for decays to an electron or muon and a b-quark
Recommended from our members
Search for electroweak production of supersymmetric particles in final states with two or three leptons at vs=1113 TeV with the ATLAS detector
A search for the electroweak production of charginos, neutralinos and sleptons decaying into final states involving two or three electrons or muons is presented. The analysis is based on 36.1 fb-1 of vs = 13 TeV proton– proton collisions recorded by the ATLAS detector at the Large Hadron Collider. Several scenarios based on simplified models are considered. These include the associated production of the next-to-lightest neutralino and the lightest chargino, followed by their decays into final states with leptons and the lightest neutralino via either sleptons or Standard Model gauge bosons; direct production of chargino pairs, which in turn decay into leptons and the lightest neutralino via intermediate sleptons; and slepton pair production, where each slepton decays directly into the lightest neutralino and a lepton. No significant deviations from the Standard Model expectation are observed and stringent limits at 95% confidence level are placed on the masses of relevant supersymmetric particles in each of these scenarios. For a massless lightest neutralino, masses up to 580 GeV are excluded for the associated production of the next-to-lightest neutralino and the lightest chargino, assuming gauge-boson mediated decays, whereas for slepton-pair production masses up to 500 GeV are excluded assuming three generations of massdegenerate sleptons
Recommended from our members
Measurement of the nuclear modification factor for inclusive jets in Pb+Pb collisions at vsNN=5.02 TeV with the ATLAS detector
Measurements of the yield and nuclear modification factor, RAA, for inclusive jet production are performed using 0.49nb-1of Pb+Pb data at vsNN=5.02TeVand 25pb-1of pp data at vs=5.02TeVwith the ATLAS detector at the LHC. Jets are reconstructed with the anti-kt algorithm with radius parameter R =0.4and are measured over the transverse momentum range of 40–1000GeVin six rapidity intervals covering |y| <2.8. The magnitude of RAA increases with increasing jet transverse momentum, reaching a value of approximately0.6 at 1TeVin the most central collisions. The magnitude of RAA also increases towards peripheral collisions. The value of RAA is independent of rapidity at low jet transverse momenta, but it is observed to decrease with increasing rapidity at high transverse momenta
Recommended from our members
Measurement of the top quark pair production charge asymmetry in proton-proton collisions at vs=7 TeV using the ATLAS detector
This paper presents a measurement of the top quark pair (tt¯) production charge asymmetry AC using 4.7 fb-1 of proton-proton collisions at a centre-of-mass energy vs=7 TeV collected by the ATLAS detector at the LHC. A tt¯-enriched sample of events with a single lepton (electron or muon), missing transverse momentum and at least four high transverse momentum jets, of which at least one is tagged as coming from a b-quark, is selected. A likelihood fit is used to reconstruct the tt¯ event kinematics. A Bayesian unfolding procedure is employed to estimate AC at the parton-level. The measured value of the tt¯ production charge asymmetry is AC = 0.006 ± 0.010, where the uncertainty includes both the statistical and the systematic components. Differential AC measurements as a function of the invariant mass, the rapidity and the transverse momentum of the tt¯ system are also presented. In addition, AC is measured for a subset of events with large tt¯ velocity, where physics beyond the Standard Model could contribute. All measurements are consistent with the Standard Model predictions
Recommended from our members
Observation of electroweak W±Z boson pair production in association with two jets in pp collisions at vs=13 TeV with the ATLAS detector
An observation of electroweak W±Z production in association with two jets in proton–proton collisions is presented. The data collected by the ATLAS detector at the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of vs=13TeVare used, corresponding to an integrated luminosity of 36.1fb-1. Events containing three identified leptons, either electrons or muons, and two jets are selected. The electroweak production of W±Z bosons in association with two jets is measured with an observed significance of 5.3standard deviations. A fiducial cross-section for electroweak production including interference effects and for a single leptonic decay mode is measured to be sWZjj-EW= 0.57 +0.14-0.13 (stat.) +0.07-0.06 (syst.) fb. Total and differential fiducial cross-sections of the sum of W±Zjj electroweak and strong productions for several kinematic observables are also measured
Recommended from our members
Search for squarks and gluinos in final states with jets and missing transverse momentum at v s = 13 TeV with the ATLAS detector
A search for squarks and gluinos in final states containing hadronic jets, missing transverse momentum but no electrons or muons is presented. The data were recorded in 2015 by the ATLAS experiment in v s = 13 TeV proton--proton collisions at the Large Hadron Collider. No excess above the Standard Model background expectation was observed in 3.2 fb -1 of analyzed data. Results are interpreted within simplified models that assume R-parity is conserved and the neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 1.51 TeV for a simplified model incorporating only a gluino octet and the lightest neutralino, assuming the lightest neutralino is massless. For a simplified model involving the strong production of mass-degenerate first- and second-generation squarks, squark masses below 1.03 TeV are excluded for a massless lightest neutralino. These limits substantially extend the region of supersymmetric parameter space excluded by previous measurements with the ATLAS detector
Recommended from our members
Impact of cross-section uncertainties on supernova neutrino spectral parameter fitting in the Deep Underground Neutrino Experiment
A primary goal of the upcoming Deep Underground Neutrino Experiment (DUNE) is to measure the O(10) MeV neutrinos produced by a Galactic core-collapse supernova if one should occur during the lifetime of the experiment. The liquid-argon-based detectors planned for DUNE are expected to be uniquely sensitive to the νe component of the supernova flux, enabling a wide variety of physics and astrophysics measurements. A key requirement for a correct interpretation of these measurements is a good understanding of the energy-dependent total cross section σ(Eν) for charged-current νe absorption on argon. In the context of a simulated extraction of supernova νe spectral parameters from a toy analysis, we investigate the impact of σ(Eν) modeling uncertainties on DUNE's supernova neutrino physics sensitivity for the first time. We find that the currently large theoretical uncertainties on σ(Eν) must be substantially reduced before the νe flux parameters can be extracted reliably; in the absence of external constraints, a measurement of the integrated neutrino luminosity with less than 10% bias with DUNE requires σ(Eν) to be known to about 5%. The neutrino spectral shape parameters can be known to better than 10% for a 20% uncertainty on the cross-section scale, although they will be sensitive to uncertainties on the shape of σ(Eν). A direct measurement of low-energy νe-argon scattering would be invaluable for improving the theoretical precision to the needed level
Recommended from our members
Highly-parallelized simulation of a pixelated LArTPC on a GPU
The rapid development of general-purpose computing on graphics processing units (GPGPU) is allowing the implementation of highly-parallelized Monte Carlo simulation chains for particle physics experiments. This technique is particularly suitable for the simulation of a pixelated charge readout for time projection chambers, given the large number of channels that this technology employs. Here we present the first implementation of a full microphysical simulator of a liquid argon time projection chamber (LArTPC) equipped with light readout and pixelated charge readout, developed for the DUNE Near Detector. The software is implemented with an end-to-end set of GPU-optimized algorithms. The algorithms have been written in Python and translated into CUDA kernels using Numba, a just-in-time compiler for a subset of Python and NumPy instructions. The GPU implementation achieves a speed up of four orders of magnitude compared with the equivalent CPU version. The simulation of the current induced on 10^3 pixels takes around 1 ms on the GPU, compared with approximately 10 s on the CPU. The results of the simulation are compared against data from a pixel-readout LArTPC prototype
Recommended from our members
Search for heavy particles decaying into top-quark pairs using lepton-plus-jets events in proton–proton collisions at vs = 13 TeV with the ATLAS detector
A search for new heavy particles that decay into top-quark pairs is performed using data collected from proton–proton collisions at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The integrated luminosity of the data sample is 36.1 fb-1. Events consistent with top-quark pair production are selected by requiring a single isolated charged lepton, missing transverse momentum and jet activity compatible with a hadronic top-quark decay. Jets identified as likely to contain b-hadrons are required to reduce the background from other Standard Model processes. The invariant mass spectrum of the candidate top-quark pairs is examined for local excesses above the background expectation. No significant deviations from the Standard Model predictions are found. Exclusion limits are set on the production cross-section times branching ratio for hypothetical Z bosons, Kaluza–Kein gluons and Kaluza–Klein gravitons that decay into top-quark pairs
- …