Publications (4)0 Total impact
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Georges Aad,
Brad Abbott,
Jalal Abdallah,
Ahmed Ali Abdelalim,
Abdelouahab Abdesselam,
Ovsat Abdinov,
Babak Abi,
Maris Abolins,
Halina Abramowicz,
Henso Abreu, [......],
Robert Zitoun,
Lidija Zivkovic,
Viatcheslav Zmouchko,
Georg Zobernig,
Antonio Zoccoli,
Yves Zolnierowski,
Andras Zsenei,
Martin zur Nedden,
Vishnu Zutshi,
Lukasz Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A measurement of the cross section for the inclusive production of isolated prompt photons in $pp$ collisions at a centre-of-mass energy $\sqrt(s)$ = 7 TeV is presented. The measurement covers the pseudorapidity ranges $|\eta^{\gamma}| < 1.37$ and $1.52 \leq |\eta^{\gamma}| < 1.81$ in the transverse energy range $15 \leq E^{\gamma}_T\ \leq 100~GeV$. The results are based on an integrated luminosity of $880~nb^{−1}$ , collected with the ATLAS detector at the Large Hadron Collider. Photon candidates are identified by combining information from the calorimeters and from the inner detector. Residual background in the selected sample is estimated from data based on the observed distribution of the transverse isolation energy in a narrow cone around the photon candidate. The results are compared to predictions from next-to-leading order perturbative QCD calculations.
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Georges Aad,
Brad Abbott,
Jalal Abdallah,
Ahmed Ali Abdelalim,
Abdelouahab Abdesselam,
Ovsat Abdinov,
Babak Abi,
Maris Abolins,
Halina Abramowicz,
Henso Abreu, [......],
Robert Zitoun,
Lidija Zivkovic,
Viatcheslav Zmouchko,
Georg Zobernig,
Antonio Zoccoli,
Yves Zolnierowski,
Andras Zsenei,
Martin zur Nedden,
Vishnu Zutshi,
Lukasz Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: 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 the highest-$p_T$ 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, $p_T$ density, and average $p_T$ are measured. The data show a higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data.
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Georges Aad,
Brad Abbott,
Jalal Abdallah,
Ahmed Ali Abdelalim,
Abdelouahab Abdesselam,
Ovsat Abdinov,
Babak Abi,
Maris Abolins,
Halina Abramowicz,
Henso Abreu, [......],
Robert Zitoun,
Lidija Zivkovic,
Viatcheslav Zmouchko,
Georg Zobernig,
Antonio Zoccoli,
Yves Zolnierowski,
Andras Zsenei,
Martin zur Nedden,
Vishnu Zutshi,
Lukasz Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: A measurement of the production cross-section for top quark pairs($t\bar{t}$) in $pp$ collisions at $\sqrt{s}$=7 TeV is presented using data recorded with the ATLAS detector at the Large Hadron Collider. Events are selected in two different topologies: single lepton (electron $e$ or muon $\mu$) with large missing transverse energy and at least four jets, and dilepton ($ee$, $\mu\mu$ or $e\mu$) with large missing transverse energy and at least two jets. In a data sample of 2.9 pb-1, 37 candidate events are observed in the single-lepton topology and 9 events in the dilepton topology. The corresponding expected backgrounds from non-$t\bar{t}$ Standard Model processes are estimated using data-driven methods and determined to be $12.2 \pm 3.9$ events and $2.5 \pm 0.6$ events, respectively. The kinematic properties of the selected events are consistent with SM $t\bar{t}$ production. The inclusive top quark pair production cross-section is measured to be $\sigma_{t\bar{t}} = 145 \pm 31 ^{+42}_{-27}$ pb where the first uncertainty is statistical and the second systematic. The measurement agrees with perturbative QCD calculations.
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Georges Aad,
Brad Abbott,
Jalal Abdallah,
Ahmed Ali Abdelalim,
Abdelouahab Abdesselam,
Ovsat Abdinov,
Babak Abi,
Maris Abolins,
Halina Abramowicz,
Henso Abreu, [......],
Robert Zitoun,
Lidija Zivkovic,
Viatcheslav Zmouchko,
Georg Zobernig,
Antonio Zoccoli,
Yves Zolnierowski,
Andras Zsenei,
Martin zur Nedden,
Vishnu Zutshi,
Lukasz Zwalinski
[show abstract]
[hide abstract]
ABSTRACT: Measurements of luminosity obtained using the ATLAS detector during early running of the Large Hadron Collider (LHC) at sqrt(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 mu, the average number of inelastic interactions per bunch crossing. Residual time- and mu-dependence between the methods is less than 2% for 0<mu<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.
