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Akdogan, T.

Publications and source records attributed to Akdogan, T..

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Search for the Higgs Boson in the H{yields}WW{yields}l{nu}jj Decay Channel in pp Collisions at {radical}(s)=7 TeV with the ATLAS Detector

A search for a Higgs boson has been performed in the H{yields}WW{yields}l{nu}jj channel in 1.04 fb{sup -1} of pp collision data at {radical}(s)=7 TeV recorded with the ATLAS detector at the Large Hadron Collider. No significant excess of events is observed over the expected background and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range 240 GeV<m{sub H}<600 GeV. The best sensitivity is reached for m{sub H}=400 GeV, where the 95% confidence level upper bound on the cross section for H{yields}WW production is 3.1 pb, or 2.7 times the standard model prediction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement of the inclusive and dijet cross-sections of b-jets in pp collisions at $\sqrt{s}=7\mbox{~TeV}$ with the ATLAS detector

The inclusive and dijet production cross-sections have been measured for jets containing b-hadrons (b-jets) in proton–proton collisions at a centre-of-mass energy of s√=7~TeVs=7~TeV , using the ATLAS detector at the LHC. The measurements use data corresponding to an integrated luminosity of 34 pb -1 . The b-jets are identified using either a lifetime-based method, where secondary decay vertices of b-hadrons in jets are reconstructed using information from the tracking detectors, or a muon-based method where the presence of a muon is used to identify semileptonic decays of b-hadrons inside jets. The inclusive b-jet cross-section is measured as a function of transverse momentum in the range 20 T <400 GeV and rapidity in the range |y|<2.1. The $b\bar{b}$ -dijet cross-section is measured as a function of the dijet invariant mass in the range 110< m jj <760 GeV, the azimuthal angle difference between the two jets and the angular variable χ in two dijet mass regions. The results are compared with next-to-leading-order QCD predictions. Finally, good agreement is observed between the measured cross-sections and the predictions obtained using POWHEG + Pythia. MC@NLO + Herwig shows good agreement with the measured $b\bar{b}$-dijet cross-section. However, it does not reproduce the measured inclusive cross-section well, particularly for central b-jets with large transverse momenta.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement of the jet fragmentation function and transverse profile in proton–proton collisions at a center-of-mass energy of 7 TeV with the ATLAS detector

The jet fragmentation function and transverse profile for jets with 25 GeV < p T jet < 500 GeV and |η jet | < 1.2 produced in proton–proton collisions with a center-of-mass energy of 7 TeV are presented. The measurement is performed using data with an integrated luminosity of 36 pb –1 . Jets are reconstructed and their momentum measured using calorimetric information. The momenta of the charged particle constituents are measured using the tracking system. The distributions corrected for detector effects are compared with various Monte Carlo event generators and generator tunes. Several of these choices show good agreement with the measured fragmentation function. Furthermore, none of these choices reproduce both the transverse profile and fragmentation function over the full kinematic range of the measurement.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Search for new phenomena in final states with large jet multiplicities and missing transverse momentum using $\sqrt {s}$ = 7 TeV pp collisions with the ATLAS detector

Results are presented of a search for any particle(s) decaying to six or more jets in association with missing transverse momentum. The search is performed using 1.34 fb -1 of $\sqrt {s}$ = 7 TeV proton-proton collisions recorded by the ATLAS detector during 2011. Data-driven techniques are used to determine the backgrounds in kinematic regions that require at least six, seven or eight jets, well beyond the multiplicities required in previous analyses. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a supersymmetry model (MSUGRA/CMSSM) where they extend previous constraints.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Search for new phenomena with the monojet and missing transverse momentum signature using the ATLAS detector in root s=7 TeV proton-proton collisions

A search for new phenomena in events featuring a high energy jet and large missing transverse momentum in proton-proton collisions at {radical}s = 7 TeV is presented using a dataset corresponding to an integrated luminosity of 33 pb{sup -1} recorded with the ATLAS detector at the Large Hadron Collider. The number of observed events is consistent with the Standard Model prediction. This result is interpreted in terms of limits on a model of Large Extra Dimensions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement of multi-jet cross sections in proton–proton collisions at a 7 TeV center-of-mass energy

Inclusive multi-jet production is studied in proton–proton collisions at a center-of-mass energy of 7 TeV, using the ATLAS detector. The data sample corresponds to an integrated luminosity of 2.4 pb -1 . Results on multi-jet cross sections are presented and compared to both leading-order plus parton-shower Monte Carlo predictions and to next-to-leading-order QCD calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Search for neutral MSSM Higgs bosons decaying to tau(+)tau(-) pairs in proton-proton collisions root s=7 TeV with the ATLAS detector

A search for neutral Higgs bosons decaying to pairs of {tau} leptons with the ATLAS detector at the LHC is presented. The analysis is based on proton-proton collisions at a center-of-mass energy of 7 TeV, recorded in 2010 and corresponding to an integrated luminosity of 36 pb{sup -1}. After signal selection, 276 events are observed in this data sample. The observed number of events is consistent with the total expected background of 269 {+-} 36 events. Exclusion limits at the 95% confidence level are derived for the production cross section of a generic Higgs boson {phi} as a function of the Higgs boson mass and for A/H/h production in the Minimal Supersymmetric Standard Model (MSSM) as a function of the parameters m{sub A} and tan {beta}.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Inclusive search for same-sign dilepton signatures in pp collisions at $ \sqrt {s} = 7 $ TeV with the ATLAS detector

An inclusive search is presented for new physics in events with two isolated leptons (e or μ) having the same electric charge. The data are selected from events collected from pp collisions at √s = 7 TeV by the ATLAS detector and correspond to an integrated luminosity of 34 pb –1 . The spectra in dilepton invariant mass, missing transverse momentum and jet multiplicity are presented and compared to Standard Model predictions. In this event sample, no evidence is found for contributions beyond those of the Standard Model. Limits are set on the cross-section in a fiducial region for new sources of same-sign high-mass dilepton events in the ee, eμ and μμ channels. Four models predicting same-sign dilepton signals are constrained: two descriptions of Majorana neutrinos, a cascade topology similar to supersymmetry or universal extra dimensions, and fourth generation d-type quarks. Assuming a new physics scale of 1 TeV, Majorana neutrinos produced by an effective operator V with masses below 460 GeV are excluded at 95% confidence level. In conclusion, a lower limit of 290 GeV is set at 95% confidence level on the mass of fourth generation d-type quarks.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Search for diphoton events with large missing transverse energy with 36 pb –1 of 7 TeV proton–proton collision data with the ATLAS detector

Making use of 36 pb –1 of proton–proton collision data at √s = 7 TeV, the ATLAS Collaboration has performed a search for diphoton events with large missing transverse energy. Observing no excess of events above the Standard Model prediction, a 95% Confidence Level (CL) upper limit is set on the cross section for new physics of σ<0.38–0.65 pb in the context of a generalised model of gauge-mediated supersymmetry breaking (GGM) with a bino-like lightest neutralino, and of σ<0.18–0.23 pb in the context of a specific model with one universal extra dimension (UED). A 95% CL lower limit of 560 GeV, for bino masses above 50 GeV, is set on the GGM gluino mass, while a lower limit of 1/ R >961 GeV is set on the UED compactification radius R . In conclusion, these limits provide the most stringent tests of these models to date.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Properties of jets measured from tracks in proton-proton collisions at center-of-mass energy √s=7 TeV with the ATLAS detector

Jets are identified and their properties studied in center-of-mass energy √s=7 TeV proton-proton collisions at the Large Hadron Collider using charged particles measured by the ATLAS inner detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and their characteristics in the transition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the anti-k t algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and corrected to charged particle-level truth jets. The transverse momenta and longitudinal momentum fractions of charged particles within jets are measured, along with the charged particle multiplicity and the particle density as a function of radial distance from the jet axis. Comparison of the data with the theoretical models implemented in existing tunings of Monte Carlo event generators indicates reasonable overall agreement between data and Monte Carlo. These comparisons are sensitive to Monte Carlo parton showering, hadronization, and soft physics models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Limits on the production of the standard model Higgs boson in pp collisions at $\sqrt{s} = 7$ TeV with the ATLAS detector

A search for the Standard Model Higgs boson at the Large Hadron Collider (LHC) running at a centre-of-mass energy of 7 TeV is reported, based on a total integrated luminosity of up to 40 pb -1 collected by the ATLAS detector in 2010. Several Higgs boson decay channels: H→γγ, H→ZZ (*) →ℓℓℓℓ, H→ZZ→ℓℓνν, H→ZZ→ℓℓqq, H→WW (*) →ℓνℓν and H→WW→ℓνqq (ℓ is e, μ) are combined in a mass range from 110 GeV to 600 GeV. The highest sensitivity is achieved in the mass range between 160 GeV and 170 GeV, where the expected 95% CL exclusion sensitivity is at Higgs boson production cross sections 2.3 times the Standard Model prediction. Upper limits on the cross section for its production are determined. Models with a fourth generation of heavy leptons and quarks with Standard Model-like couplings to the Higgs boson are also investigated and are excluded at 95% CL for a Higgs boson mass in the range from 140 GeV to 185 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement of Wγ and Zγ production in proton-proton collisions at $ \sqrt {s} = 7 $ TeV with the ATLAS detector

We present studies of W and Z bosons with associated high energy photons produced in pp collisions at √s = 7TeV. The analysis uses 35 pb -1 of data collected by the ATLAS experiment in 2010. The event selection requires W and Z bosons decaying into high p T leptons (electrons or muons) and a photon with E T > 15 GeV separated from the lepton(s) by a distance ΔR(l,γ) > 0.7 in η-Φ space. A total of 95 (97) pp → e ± νγ + X(pp → μ ± νγ + X) and 25 (23) pp → e + e - γ + X(pp → μ + μ - γ+X) event candidates are selected. The kinematic distributions of the leptons and photons and the production cross sections are measured. The data are found to agree with Standard Model predictions that include next-to-leading-order O(αα s ) contributions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

Measurement of dijet production with a veto on additional central jet activity in pp collisions at $ \sqrt {s} = 7 $ TeV using the ATLAS detector

A measurement of jet activity in the rapidity interval bounded by a dijet system is presented. Events are vetoed if a jet with transverse momentum greater than 20 GeV is found between the two boundary jets. The fraction of dijet events that survive the jet veto is presented for boundary jets that are separated by up to six units of rapidity and with mean transverse momentum 50 < p¯ T < 500 GeV. The mean multiplicity of jets above the veto scale in the rapidity interval bounded by the dijet system is also presented as an alternative method for quantifying perturbative QCD emission. The data are compared to a next-to-leading order plus parton shower prediction from the powheg-box, an all-order resummation using the hej calculation and the pythia, herwig++ and alpgen event generators. In conclusion, the measurement was performed using pp collisions at √s = 7 TeV using data recorded by the ATLAS detector in 2010.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗