ATLAS Collaboration(Aad, G. et al), Bernabeu Verdu, J., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., et al. (2014). Operation and performance of the ATLAS semiconductor tracker. J. Instrum., 9, P08009–73pp.
Abstract: The semiconductor tracker is a silicon microstrip detector forming part of the inner tracking system of the ATLAS experiment at the LHC. The operation and performance of the semiconductor tracker during the first years of LHC running are described. More than 99% of the detector modules were operational during this period, with an average intrinsic hit efficiency of (99.74 +/- 0.04)%. The evolution of the noise occupancy is discussed, and measurements of the Lorentz angle, delta-ray production and energy loss presented. The alignment of the detector is found to be stable at the few-micron level over long periods of time. Radiation damage measurements, which include the evolution of detector leakage currents, are found to be consistent with predictions and are used in the verification of radiation background simulations.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2018). Measurement of jet fragmentation in 5.02 TeV proton-lead and proton-proton collisions with the ATLAS detector. Nucl. Phys. A, 978, 65–106.
Abstract: A measurement of the fragmentation functions of jets into charged particles in p Pb collisions and pp collisions is presented. The analysis utilizes 28 nb(-1) of p Pb data and 26 pb(-1) of pp data, both at root(TN)-T-s= 5.02 TeV, collected in 2013 and 2015, respectively, with the ATLAS detector at the LHC. The measurement is reported in the centre-of-mass frame of the nucleon-nucleon system for jets in the rapidity range vertical bar y*vertical bar <1.6 and with transverse momentum 45 < p(T) < 260 GeV. Results are presented both as a function of the charged-particle transverse momentum and as a function of the longitudinal momentum fraction of the particle with respect to the jet. The pp fragmentation functions are compared with results from Monte Carlo event generators and two theoretical models. The ratios of the p +Pb to pp fragmentation functions are found to be consistent with unity. (C) 2018 CERN for the benefit of the ATLAS Collaboration.
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ATLAS Collaboration(Aad, G. et al), Aparisi Pozo, J. A., Bailey, A. J., Cabrera Urban, S., Cardillo, F., Castillo, F. L., et al. (2021). Measurements of sensor radiation damage in the ATLAS inner detector using leakage currents. J. Instrum., 16(8), P08025–46pp.
Abstract: Non-ionizing energy loss causes bulk damage to the silicon sensors of the ATLAS pixel and strip detectors. This damage has important implications for data-taking operations, charged-particle track reconstruction, detector simulations, and physics analysis. This paper presents simulations and measurements of the leakage current in the ATLAS pixel detector and semiconductor tracker as a function of location in the detector and time, using data collected in Run 1 (2010-2012) and Run 2 (2015-2018) of the Large Hadron Collider. The extracted fluence shows a much stronger vertical bar z vertical bar-dependence in the innermost layers than is seen in simulation. Furthermore, the overall fluence on the second innermost layer is significantly higher than in simulation, with better agreement in layers at higher radii. These measurements are important for validating the simulation models and can be used in part to justify safety factors for future detector designs and interventions.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Dynamics of isolated-photon plus jet production in pp collisions at root s=7 TeV with the ATLAS detector. Nucl. Phys. B, 875(3), 483–535.
Abstract: The dynamics of isolated-photon plus jet production in pp collisions at a centre-of-mass energy of 7 TeV has been studied with the ATLAS detector at the LHC using an integrated luminosity of 37 pb(-1). Measurements of isolated-photon plus jet bin-averaged cross sections are presented as functions of photon transverse energy, jet transverse momentum and jet rapidity. In addition, the bin-averaged cross sections as functions of the difference between the azimuthal angles of the photon and the jet, the photon jet invariant mass and the scattering angle in the photon jet centre-of-mass frame have been measured. Next-to-leading-order QCD calculations are compared to the measurements and provide a good description of the data, except for the case of the azimuthal opening angle.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., Ferrer, A., et al. (2015). Measurement of charged-particle spectra in Pb plus Pb collisions at root s(NN)=2.76 TeV with the ATLAS detector at the LHC. J. High Energy Phys., 09(9), 050–51pp.
Abstract: Charged-particle spectra obtained in Pb+Pb interactions at root s(NN) = 2.76TeV and pp interactions at root s(NN) = 2.76TeV with the ATLAS detector at the LHC are presented, using data with integrated luminosities of 0.15 nb(-1) and 4.2 pb(-1), respectively, in a wide transverse momentum (0.5 < p(T) < 150 GeV) and pseudorapidity (vertical bar eta vertical bar < 2) range. For Pb+Pb collisions, the spectra are presented as a function of collision centrality, which is determined by the response of the forward calorimeters located on both sides of the interaction point. The nuclear modification factors R-AA and R-CP are presented in detail as a function of centrality, p(T) and eta. They show a distinct p(T)-dependence with a pronounced minimum at about 7 GeV. Above 60 GeV, R-AA is consistent with a plateau at a centrality-dependent value, within the uncertainties. The value is 0.55 +/- 0.01(stat.) +/- 0.04(syst.) in the most central collisions. The R-AA distribution is consistent with flat vertical bar eta vertical bar dependence over the whole transverse momentum range in all centrality classes.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2012). Measurements of the electron and muon inclusive cross-sections in proton-proton collisions at root s=7 TeV with the ATLAS detector. Phys. Lett. B, 707(5), 438–458.
Abstract: This Letter presents measurements of the differential cross-sections for inclusive electron and muon production in proton-proton collisions at a centre-of-mass energy of root s = 7 TeV, using data collected by the ATLAS detector at the LHC. The muon cross-section is measured as a function of p(T) in the range 4 < p(T) < 100 GeV and within pseudorapidity vertical bar eta vertical bar < 2.5. In addition the electron and muon cross-sections are measured in the range 7 < p(T) < 26 GeV and within vertical bar eta vertical bar < 2.0, excluding 1.37 < vertical bar eta vertical bar < 1.52. Integrated luminosities of 1.3 pb(-1) and 1.4 pb(-1) are used for the electron and muon measurements, respectively. After subtraction of the W/Z/gamma* contribution, the differential cross-sections are found to be in good agreement with theoretical predictions for heavy-flavour production obtained from Fixed Order NLO calculations with NLL high-p(T) resummation, and to be sensitive to the effects of NLL resummation.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Ferrer, A., Fiorini, L., et al. (2012). Measurement of the b-hadron production cross section using decays to D*(+)mu X- final states in pp collisions at root s=7 TeV with the ATLAS detector. Nucl. Phys. B, 864(3), 341–381.
Abstract: The b-hadron production cross section is measured with the ATLAS detector in pp collisions at root s = 7 TeV, using 3.3 pb(-1) of integrated luminosity, collected during the 2010 LHC run. The b-hadrons are selected by partially reconstructing D*(+)mu X- final states. Differential cross sections are measured as functions of the transverse momentum and pseudorapidity. The measured production cross section for a b-hadron with p(T) > 9 GeV and vertical bar eta vertical bar < 2.5 is 32.7 +/- 0.8(stat.)(-6.8)(+4.5)(syst.) μb, higher than the next-to-leading-order QCD predictions but consistent within the experimental and theoretical uncertainties.
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ATLAS Collaboration(Aad, G. et al), Amoros, G., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Escobar, C., et al. (2011). Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)=7 TeV using 35 pb(-1) of ATLAS data. Phys. Lett. B, 706(2-3), 150–167.
Abstract: A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges vertical bar eta vertical bar < 1.37 and 1.52 <= vertical bar eta vertical bar < 2.37 in the transverse energy range 45 <= E(T) < 400 GeV. The results are based on an integrated luminosity of 35 pb(-1), collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.
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ATLAS Collaboration(Aad, G. et al), Alvarez Piqueras, D., Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fernandez Martinez, P., et al. (2015). Modelling Z -> ττ processes in ATLAS with τ-embedded Z -> μμ data. J. Instrum., 10, P09018–41pp.
Abstract: This paper describes the concept, technical realisation and validation of a largely data-driven method to model events with Z -> tau tau decays. In Z -> μμevents selected from proton-proton collision data recorded at root s = 8 TeV with the ATLAS experiment at the LHC in 2012, the Z decay muons are replaced by tau leptons from simulated Z -> tau tau decays at the level of reconstructed tracks and calorimeter cells. The tau lepton kinematics are derived from the kinematics of the original muons. Thus, only the well-understood decays of the Z boson and tau leptons as well as the detector response to the tau decay products are obtained from simulation. All other aspects of the event, such as the Z boson and jet kinematics as well as effects from multiple interactions, are given by the actual data. This so-called tau-embedding method is particularly relevant for Higgs boson searches and analyses in tau tau final states, where Z -> tau tau decays constitute a large irreducible background that cannot be obtained directly from data control samples. In this paper, the relevant concepts are discussed based on the implementation used in the ATLAS Standard Model H -> tau tau analysis of the full datataset recorded during 2011 and 2012.
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Characterisation and mitigation of beam-induced backgrounds observed in the ATLAS detector during the 2011 proton-proton run. J. Instrum., 8, P07004–72pp.
Abstract: This paper presents a summary of beam-induced backgrounds observed in the ATLAS detector and discusses methods to tag and remove background contaminated events in data. Trigger-rate based monitoring of beam-related backgrounds is presented. The correlations of backgrounds with machine conditions, such as residual pressure in the beam-pipe, are discussed. Results from dedicated beam-background simulations are shown, and their qualitative agreement with data is evaluated. Data taken during the passage of unpaired, i.e. non-colliding, proton bunches is used to obtain background-enriched data samples. These are used to identify characteristic features of beam-induced backgrounds, which then are exploited to develop dedicated background tagging tools. These tools, based on observables in the Pixel detector, the muon spectrometer and the calorimeters, are described in detail and their efficiencies are evaluated. Finally an example of an application of these techniques to a monojet analysis is given, which demonstrates the importance of such event cleaning techniques for some new physics searches.
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