Radial Scaling in Inclusive Jet Production at Hadron Colliders

Inclusive jet production in p-p and pbar-p collisions shows many of the same kinematic systematics as observed in single particle inclusive production at much lower energies. In an earlier study (1974) a phenomenology, called radial scaling, was developed for the single particle inclusive cross sections that attempted to capture the essential underlying physics of point-like parton scattering and the fragmentation of partons into hadrons suppressed by the kinematic boundary. The phenomenology was successful in emphasizing the underlying systematics of the inclusive particle productions. Here we demonstrate that inclusive jet production at the LHC in high-energy p-p collisions and at the Tevatron in pbar-p inelastic scattering show similar behavior. The ATLAS inclusive jet production plotted as a function of this scaling variable is studied for sqrt(s) of 2.76, 7 and 13 TeV and is compared to pbar-p inclusive jet production at 1.96 TeV measured at the CDF and D0 at the Tevatron and p-Pb inclusive jet production at the LHC ATLAS at sqrt(sNN) = 5.02 TeV. Inclusive single particle production at FNAL fixed target and ISR energies are compared to inclusive J/Psi production at the LHC measured in ATLAS, CMS and LHCb. Striking common features of the data are discussed.Comment: 47 pages, 22 figures, 6 tables. Version 2 - more data added, references enhance

Search for direct production of charginos, neutralinos and sleptons in final states with two leptons and missing transverse momentum in pp collisions at √s = 8 TeV with the ATLAS detector

Searches for the electroweak production of charginos, neutralinos and sleptons in final states characterized by the presence of two leptons (electrons and muons) and missing transverse momentum are performed using 20.3 fb[superscript −1] of proton-proton collision data at √s = 8 TeV recorded with the ATLAS experiment at the Large Hadron Collider. No significant excess beyond Standard Model expectations is observed. Limits are set on the masses of the lightest chargino, next-to-lightest neutralino and sleptons for different lightest-neutralino mass hypotheses in simplified models. Results are also interpreted in various scenarios of the phenomenological Minimal Supersymmetric Standard Model.United States. Dept. of EnergyNational Science Foundation (U.S.)Brookhaven National Laborator

Measurement of the production of a W boson in association with a charm quark in pp collisions at √s = 7 TeV with the ATLAS detector

The production of a W boson in association with a single charm quark is studied using 4.6 fb[superscript −1] of pp collision data at √s = 7 TeV collected with the ATLAS detector at the Large Hadron Collider. In events in which a W boson decays to an electron or muon, the charm quark is tagged either by its semileptonic decay to a muon or by the presence of a charmed meson. The integrated and differential cross sections as a function of the pseudorapidity of the lepton from the W-boson decay are measured. Results are compared to the predictions of next-to-leading-order QCD calculations obtained from various parton distribution function parameterisations. The ratio of the strange-to-down sea-quark distributions is determined to be 0.96[+0.26 over −0.30] at Q [superscript 2] = 1.9 GeV[superscript 2], which supports the hypothesis of an SU(3)-symmetric composition of the light-quark sea. Additionally, the cross-section ratio σ(W [superscript +] + [bar over c])/σ(W [superscript −] + c) is compared to the predictions obtained using parton distribution function parameterisations with different assumptions about the s − [bar over s] quark asymmetry.United States. Dept. of EnergyNational Science Foundation (U.S.)Brookhaven National Laborator

Jet energy measurement and its systematic uncertainty in proton–proton collisions at √s = 7 TeV with the ATLAS detector

The jet energy scale (JES) and its systematic uncertainty are determined for jets measured with the ATLAS detector using proton–proton collision data with a centre-of-mass energy of s√=7 TeV corresponding to an integrated luminosity of 4.7 fb [superscript −1]. Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-k[subscript t] algorithm with distance parameters R=0.4 or R=0.6 , and are calibrated using MC simulations. A residual JES correction is applied to account for differences between data and MC simulations. This correction and its systematic uncertainty are estimated using a combination of in situ techniques exploiting the transverse momentum balance between a jet and a reference object such as a photon or a Z boson, for 20≤p[jet over T]1 TeV. The calibration of forward jets is derived from dijet p[subscript T] balance measurements. The resulting uncertainty reaches its largest value of 6 % for low- p[subscript T] jets at |η|=4.5 . Additional JES uncertainties due to specific event topologies, such as close-by jets or selections of event samples with an enhanced content of jets originating from light quarks or gluons, are also discussed. The magnitude of these uncertainties depends on the event sample used in a given physics analysis, but typically amounts to 0.5–3 %.United States. Dept. of EnergyNational Science Foundation (U.S.)Brookhaven National Laborator

Search for dark matter candidates and large extra dimensions in events with a jet and missing transverse momentum with the ATLAS detector

A search for new phenomena in events with a high-energy jet and large missing transverse momentum is performed using data from proton-proton collisions at √s = 7 TeV with the ATLAS experiment at the Large Hadron Collider. Four kinematic regions are explored using a dataset corresponding to an integrated luminosity of 4.7 fb[superscript −1]. No excess of events beyond expectations from Standard Model processes is observed, and limits are set on large extra dimensions and the pair production of dark matter particles.United States. Dept. of EnergyNational Science Foundation (U.S.)Brookhaven National Laborator

Measurement of the pseudorapidity and transverse momentum dependence of the elliptic flow of charged particles in lead–lead collisions at √sNN = 2.76 TeV with the ATLAS detector

This Letter describes the measurement of elliptic flow of charged particles in lead–lead collisions at √s[subscript NN]=2.76 TeV using the ATLAS detector at the Large Hadron Collider (LHC). The results are based on an integrated luminosity of approximately 7 μb[superscript −1]. Elliptic flow is measured over a wide region in pseudorapidity, |η|<2.5|, and over a broad range in transverse momentum, 0.5<pT<20 GeV. The elliptic flow parameter v2 is obtained by correlating individual tracks with the event plane measured using energy deposited in the forward calorimeters. As a function of transverse momentum, v2(pT) reaches a maximum at pT of about 3 GeV, then decreases and becomes weakly dependent on pT above 7–8 GeV. Over the measured pseudorapidity region, v2 is found to be only weakly dependent on η, with less variation than observed at lower beam energies. The results are discussed in the context of previous measurements at lower collision energies, as well as recent results from the LHC.United States. Dept. of EnergyNational Science Foundation (U.S.

Measurement of the t-channel single top-quark production cross section in pp collisions at √s = 7 TeV with the ATLAS detector

We report a measurement of the cross section of single top-quark production in the t -channel using 1.04 fb[superscript −1] of pp collision data at √s = 7 TeV recorded with the ATLAS detector at the LHC. Selected events feature one electron or muon, missing transverse momentum, and two or three jets, exactly one of them identified as originating from a b quark. The cross section is measured by fitting the distribution of a multivariate discriminant constructed with a neural network, yielding [formula] which is in good agreement with the prediction of the Standard Model. Using the ratio of the measured to the theoretically predicted cross section and assuming that the top-quark-related CKM matrix elements obey the relation |Vtb|>>|Vts|, |Vtd|, the coupling strength at the W -t -b vertex is determined to be . If it is assumed that |Vtb|[less than or equal to] 1 a lower limit of [formula] is obtained at the 95% confidence level.Brookhaven National LaboratoryUnited States. Dept. of EnergyNational Science Foundation (U.S.

Search for the Standard Model Higgs boson in the decay channel H→ZZ(*)→4ℓ with the ATLAS detector

A search for the Standard Model Higgs boson in the decay channel H→ZZ(*)→ℓ[superscript +]ℓ[superscript −]ℓ′[superscript +]ℓ′[superscript −], where ℓ=e,μ is presented. Proton–proton collision data at √s = 7 TeV recorded with the ATLAS detector and corresponding to an average integrated luminosity of 2.1 fb[superscript −1] are compared to the Standard Model expectations. Upper limits on the production cross section of a Standard Model Higgs boson with a mass between 110 and 600 GeV600 GeV are derived. The observed (expected) 95% confidence level upper limit on the production cross section for a Higgs boson with a mass of 194 GeV, the region with the best expected sensitivity for this search, is 0.99 (1.01) times the Standard Model prediction. The Standard Model Higgs boson is excluded at 95% confidence level in the mass ranges 191–197, 199–200 and 214–224 GeV.European Organization for Nuclear ResearchUnited States. Dept. of EnergyNational Science Foundation (U.S.)Brookhaven National Laborator

Search for metastable heavy charged particles with large ionisation energy loss in pp collisions at √s = 8 TeV using the ATLAS experiment

Many extensions of the Standard Model predict the existence of charged heavy long-lived particles, such as R-hadrons or charginos. These particles, if produced at the Large Hadron Collider, should be moving non-relativistically and are therefore identifiable through the measurement of an anomalously large specific energy loss in the ATLAS pixel detector. Measuring heavy long-lived particles through their track parameters in the vicinity of the interaction vertex provides sensitivity to metastable particles with lifetimes from 0.6 ns to 30 ns. A search for such particles with the ATLAS detector at the Large Hadron Collider is presented, based on a data sample corresponding to an integrated luminosity of 18.4 fb [superscript −1] of pp collisions at √s = 8 TeV. No significant deviation from the Standard Model background expectation is observed, and lifetime-dependent upper limits on R-hadrons and chargino production are set. Gluino R-hadrons with 10 ns lifetime and masses up to 1185 GeV are excluded at 95 %% confidence level, and so are charginos with 15 ns lifetime and masses up to 482 GeV.United States. Department of EnergyNational Science Foundation (U.S.

ATLAS search for new phenomena in dijet mass and angular distributions using pp collisions at √s =7 TeV

Mass and angular distributions of dijets produced in LHC proton-proton collisions at a centre-of-mass energy √s = 7 TeV have been studied with the ATLAS detector using the full 2011 data set with an integrated luminosity of 4.8 fb[superscript −1]. Dijet masses up to ~ 4.0 TeV have been probed. No resonance-like features have been observed in the dijet mass spectrum, and all angular distributions are consistent with the predictions of QCD. Exclusion limits on six hypotheses of new phenomena have been set at 95% CL in terms of mass or energy scale, as appropriate. These hypotheses include excited quarks below 2.83 TeV, colour octet scalars below 1.86 TeV, heavy W bosons below 1.68 TeV, string resonances below 3.61 TeV, quantum black holes with six extra space-time dimensions for quantum gravity scales below 4.11 TeV, and quark contact interactions below a compositeness scale of 7.6 TeV in a destructive interference scenario.United States. Dept. of EnergyNational Science Foundation (U.S.)Brookhaven National Laborator