Engineering topics
Akdogan, T.
Publications and source records attributed to Akdogan, T..
Measurement of the W⁺W⁻ Cross Section in √s=7 TeV pp Collisions with ATLAS
This Letter presents a measurement of the W⁺W⁻ production cross section in √s=7 TeV pp collisions by the ATLAS experiment, using 34 pb⁻¹ of integrated luminosity produced by the Large Hadron Collider at CERN. Selecting events with two isolated leptons, each either an electron or a muon, 8 candidate events are observed with an expected background of 1.7±0.6 events. The measured cross section is 41 +20 -16 (stat)±5(syst)±1(lumi) pb, which is consistent with the standard model prediction of 44±3 pb calculated at next-to-leading order in QCD.
Search for an excess of events with an identical flavour lepton pair and significant missing transverse momentum in $\sqrt{s}=7$ TeV proton–proton collisions with the ATLAS detector
Results are presented of a search for supersymmetric particles decaying into final states with significant missing transverse momentum and exactly two identical flavour leptons (e, μ) of opposite charge in √s = 7 TeV collisions at the Large Hadron Collider. This channel is particularly sensitive to supersymmetric particle cascade decays producing flavour correlated lepton pairs. Flavour uncorrelated backgrounds are subtracted using a sample of opposite flavour lepton pair events. Observation of an excess beyond Standard Model expectations following this subtraction procedure would offer one of the best routes to measuring the masses of supersymmetric particles. In a data sample corresponding to an integrated luminosity of 35 pb⁻¹ no such excess is observed. Model-independent limits are set on the contribution to these final states from new physics and are used to exclude regions of a phenomenological supersymmetric parameter space.
Search for supersymmetric particles in events with lepton pairs and large missing transverse momentum in $\sqrt{s}=7~\mbox{TeV}$ proton–proton collisions with the ATLAS experiment
Results are presented of searches for the production of supersymmetric particles decaying into final states with missing transverse momentum and exactly two isolated leptons in √s = 7 TeV proton-proton collisions at the Large Hadron Collider. Search strategies requiring lepton pairs with identical-sign or opposite-sign electric charges are described. In a data sample corresponding to an integrated luminosity of 35 pb -1 collected with the ATLAS detector, no significant excesses are observed. Based on specific benchmark models, limits are placed on the squark mass between 450 and 690 GeV for squarks approximately degenerate in mass with gluinos, depending on the supersymmetric mass hierarchy considered.
Search for squarks and gluinos using final states with jets and missing transverse momentum with the ATLAS detector in s = 7 TeV proton–proton collisions
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Search for contact interactions in dimuon events from pp collisions at √s=7 TeV with the ATLAS detector
A search for contact interactions has been performed using dimuon events recorded with the ATLAS detector in proton-proton collisions at √s=7 TeV. The data sample corresponds to an integrated luminosity of 42 pb⁻¹. No significant deviation from the standard model is observed in the dimuon mass spectrum, allowing the following 95% C.L. limits to be set on the energy scale of contact interactions: Λ>4.9 TeV (4.5 TeV) for constructive (destructive) interference in the left-left isoscalar compositeness model. These limits are the most stringent to date for μμqq contact interactions.
Search for pair production of first or second generation leptoquarks in proton-proton collisions at √s=7 TeV using the ATLAS detector at the LHC
This paper describes searches for the pair production of first or second generation scalar leptoquarks using 35 pb⁻¹ of proton-proton collision data recorded by the ATLAS detector at s√=7 TeV. Leptoquarks are searched in events with two oppositely-charged muons or electrons and at least two jets, and in events with one muon or electron, missing transverse momentum and at least two jets. After event selection, the observed yields are consistent with the predicted backgrounds. Leptoquark production is excluded at the 95% CL for masses M LQ <376 (319) GeV and M LQ <422 (362) GeV for first and second generation scalar leptoquarks, respectively, when assuming the branching fraction of a leptoquark to a charged lepton is equal to 1.0 (0.5).
Search for high mass dilepton resonances in pp collisions at s = 7 TeV with the ATLAS experiment
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Measurement of the W charge asymmetry in the W → μ ν decay mode in pp collisions at s = 7 TeV with the ATLAS detector
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Measurement of underlying event characteristics using charged particles in pp collisions at {radical}(s)=900 GeV and 7 TeV with the ATLAS detector
Measurements of charged particle distributions, sensitive to the underlying event, have been performed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton-proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The 'underlying event' is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the proton. Three regions are defined in azimuthal angle with respect to the highest transverse momentum charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to the underlying event. In each of these regions, distributions of the charged particle multiplicity, transverse momentum density, and average p{sub T} are measured. The data show generally higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data.
A search for new physics in dijet mass and angular distributions in pp collisions at $\sqrt{s}$=7 TeV measured with the ATLAS detector
A search for new interactions and resonances produced in LHC proton-proton ( pp ) collisions at a centre-of-mass energy $\sqrt{s}$= 7 TeV has been performed with the ATLAS detector. Using a data set with an integrated luminosity of 36 pb -1 dijet mass and angular distributions have been measured up to dijet masses of ~3.5 TeV and found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% C.L. on various models for new physics: an excited quark is excluded with mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and Randall-Meade quantum black holes are excluded in models with six extra space-time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. In conclusion, analysis of the dijet angular distribution using a novel technique 18 simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale ${\Lambda}$ below 9.5 TeV.
Measurements of underlying-event properties using neutral and charged particles in pp collisions at $\sqrt{s}=900$ GeV and $\sqrt{s}=7$ TeV with the ATLAS detector at the LHC
We present first measurements of charged and neutral particle-flow correlations in pp collisions using the ATLAS calorimeters. Data were collected in 2009 and 2010 at centre-of-mass energies of 900 GeV and 7 TeV. Events were selected using a minimum-bias trigger which required a charged particle in scintillation counters on either side of the interaction point. Particle flows, sensitive to the underlying event, are measured using clusters of energy in the ATLAS calorimeters, taking advantage of their fine granularity. No Monte Carlo generator used in this analysis can accurately describe the measurements. The results are independent of those based on charged particles measured by the ATLAS tracking systems and can be used to constrain the parameters of Monte Carlo generators.
Measurement of Dijet Azimuthal Decorrelations in pp Collisions at {radical}(s)=7 TeV
Azimuthal decorrelations between the two central jets with the largest transverse momenta are sensitive to the dynamics of events with multiple jets. We present a measurement of the normalized differential cross section based on the full data set ({integral}Ldt=36 pb{sup -1}) acquired by the ATLAS detector during the 2010 {radical}(s)=7 TeV proton-proton run of the LHC. The measured distributions include jets with transverse momenta up to 1.3 TeV, probing perturbative QCD in a high-energy regime.
Luminosity determination in pp collisions at $\sqrt{s} = 7$ TeV using the ATLAS detector at the LHC
Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at √s = 7 TeV are presented. The luminosity is independently determined using several detectors and multiple algorithms, each having different acceptances, systematic uncertainties and sensitivity to background. The ratios of the luminosities obtained from these methods are monitored as a function of time and of μ, the average number of inelastic interactions per bunch crossing. Residual time- and μ-dependence between the methods is less than 2% for 0 < μ < 2.5. Absolute luminosity calibrations, performed using beam separation scans, have a common systematic uncertainty of ±11%, dominated by the measurement of the LHC beam currents. After calibration, the luminosities obtained from the different methods differ by at most ±2%. The visible cross sections measured using the beam scans are compared to predictions obtained with the PYTHIA and PHOJET event generators and the ATLAS detector simulation.