ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2016). Identification of high transverse momentum top quarks in pp collisions at root s=8 TeV with the ATLAS detector. J. High Energy Phys., 06(6), 093–81pp.
Abstract: This paper presents studies of the performance of several jet-substructure techniques, which are used to identify hadronically decaying top quarks with high transverse momentum contained in large-radius jets. The efficiency of identifying top quarks is measured using a sample of top-quark pairs and the rate of wrongly identifying jets from other quarks or gluons as top quarks is measured using multijet events collected with the ATLAS experiment in 20.3 fb(-1) of 8TeV proton-proton collisions at the Large Hadron Collider. Predictions from Monte Carlo simulations are found to provide an accurate description of the performance. The techniques are compared in terms of signal efficiency and background rejection using simulations, covering a larger range in jet transverse momenta than accessible in the dataset. Additionally, a novel technique is developed that is optimized to reconstruct top quarks in events with many jets.
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Improved luminosity determination in pp collisions at root s=7 TeV using the ATLAS detector at the LHC. Eur. Phys. J. C, 73(8), 2518–39pp.
Abstract: The luminosity calibration for the ATLAS detector at the LHC during pp collisions at root s = 7 TeV in 2010 and 2011 is presented. Evaluation of the luminosity scale is performed using several luminosity-sensitive detectors, and comparisons are made of the long-term stability and accuracy of this calibration applied to the pp collisions at root s = 7 TeV. A luminosity uncertainty of delta L/L = +/- 3.5 % is obtained for the 47 pb(-1) of data delivered to ATLAS in 2010, and an uncertainty of delta L/L = +/- 1.8 % is obtained for the 5.5 fb(-1) delivered in 2011.
|
ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Inclusive search for same-sign dilepton signatures in pp collisions at root s=7 TeV with the ATLAS detector. J. High Energy Phys., 10(10), 107–48pp.
Abstract: An inclusive search is presented for new physics in events with two isolated leptons (e or mu) having the same electric charge. The data are selected from events collected from pp collisions at root 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 ducial region for new sources of same-sign high-mass dilepton events in the ee, emu and mumu 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. A lower limit of 290 GeV is set at 95% confidence level on the mass of fourth generation d-type quarks.
|
ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2015). Jet energy measurement and its systematic uncertainty in proton-proton collisions at root s=7 TeV with the ATLAS detector. Eur. Phys. J. C, 75(1), 17–101pp.
Abstract: The jet energy scale (JES) and its systematic uncertainty are determined for jetsmeasured with the ATLAS detector using proton-proton collision data with a centre-of-mass energy of root s = 7 TeV corresponding to an integrated luminosity of 4.7 fb(-1). Jets are reconstructed from energy deposits forming topological clusters of calorimeter cells using the anti-kt algorithmwith 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(T)(jet) < 1000 GeV and pseudorapidities vertical bar eta vertical bar < 4.5. The effect of multiple proton-proton interactions is corrected for, and an uncertainty is evaluated using in situ techniques. The smallest JES uncertainty of less than 1% is found in the central calorimeter region (vertical bar eta vertical bar| < 1.2) for jets with 55 = p(T)(jet) < 500 GeV. For central jets at lower p(T), the uncertainty is about 3%. A consistent JES estimate is found using measurements of the calorimeter response of single hadrons in proton-proton collisions and test-beam data, which also provide the estimate for p(T)(jet) > 1 TeV. The calibration of forward jets is derived from dijet p(T) balance measurements. The resulting uncertainty reaches its largest value of 6% for low-p(T) jets at vertical bar eta vertical bar| = 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%.
|
ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., et al. (2013). Jet energy measurement with the ATLAS detector in proton-proton collisions at root s=7 TeV. Eur. Phys. J. C, 73(3), 2304–118pp.
Abstract: The jet energy scale and its systematic uncertainty are determined for jets measured with the ATLAS detector at the LHC in proton-proton collision data at a centre-of-mass energy of root s = 7 TeV corresponding to an integrated luminosity of 38 pb(-1). Jets are reconstructed with the anti-k(t) algorithm with distance parameters R = 0.4 or R = 0.6. Jet energy and angle corrections are determined from Monte Carlo simulations to calibrate jets with transverse momenta pT >= 20 GeV and pseudorapidities vertical bar eta vertical bar < 4.5. The jet energy systematic uncertainty is estimated using the single isolated hadron response measured in situ and in test-beams, exploiting the transverse momentum balance between central and forward jets in events with dijet topologies and studying systematic variations in Monte Carlo simulations. The jet energy uncertainty is less than 2.5 % in the central calorimeter region (vertical bar eta vertical bar < 0.8) for jets with 60 <= p(T) < 800 GeV, and is maximally 14 % for p(T) < 30 GeV in the most forward region 3.2 <= vertical bar eta vertical bar < 4.5. The jet energy is validated for jet transverse momenta up to 1 TeV to the level of a few percent using several in situ techniques by comparing a well-known reference such as the recoiling photon p(T), the sum of the transverse momenta of tracks associated to the jet, or a system of low-p(T) jets recoiling against a high-p(T) jet. More sophisticated jet calibration schemes are presented based on calorimeter cell energy density weighting or hadronic properties of jets, aiming for an improved jet energy resolution and a reduced flavour dependence of the jet response. The systematic uncertainty of the jet energy determined from a combination of in situ techniques is consistent with the one derived from single hadron response measurements over a wide kinematic range. The nominal corrections and uncertainties are derived for isolated jets in an inclusive sample of high-p(T) jets. Special cases such as event topologies with close-by jets, or selections of samples with an enhanced content of jets originating from light quarks, heavy quarks or gluons are also discussed and the corresponding uncertainties are determined.
|
