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Giromini, Paolo

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Giromini

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Paolo

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Giromini, Paolo

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2016 - 201828

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Author's Publications: search.filters.isAuthorOfPublication.9f5c46fd-33c8-427f-bae4-a6143ddc562a

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Now showing 1 - 10 of 30
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    Luminosity Determination in Pp Collisions at S√ S = 8 TeV Using the ATLAS Detector at the LHC
    Morii, Masahiro; Chan, S. K.; Clark, B; Giromini, Paolo; Franklin, Melissa; Huth, John; Ippolito, Victoria; Lazovich, Tomo; Lopez Mateos, D; Rogan, Charlotte
    The luminosity determination for the ATLAS detector at the LHC during pp collisions at s√= 8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of δℒ/ℒ = ±1.9% is obtained for the 22.7 fb-1 of pp collision data delivered to ATLAS at s√= 8 TeV in 2012.
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    Search for the Standard Model Higgs Boson Produced by Vector-Boson Fusion and Decaying to Bottom Quarks in S√=8 S = 8 TeV Pp Collisions With the ATLAS Detector
    Chan, Stephen; Clark, Brian Lee; Franklin, Melissa; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Skottowe, Hugh Philip; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Yen, Andy; Zambito, Stefano
    A search with the ATLAS detector is presented for the Standard Model Higgs boson produced by vector-boson fusion and decaying to a pair of bottom quarks, using 20.2 fb−1 of LHC proton-proton collision data at √s = 8 TeV. The signal is searched for as a resonance in the invariant mass distribution of a pair of jets containing b-hadrons in vector-boson-fusion candidate events. The yield is measured to be −0.8 ± 2.3 times the Standard Model cross-section for a Higgs boson mass of 125 GeV. The upper limit on the cross-section times the branching ratio is found to be 4.4 times the Standard Model cross- section at the 95% confidence level, consistent with the expected limit value of 5.4 (5.7) in the background-only (Standard Model production) hypothesis.
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    Reconstruction of primary vertices at the ATLAS experiment in Run 1 proton–proton collisions at the LHC
    (Springer Nature, 2017) Chan, Stephen; Clark, Brian Lee; Franklin, Melissa; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Yen, Andy; Zambito, Stefano
    This paper presents the method and performance of primary vertex reconstruction in proton-proton collision data recorded by the ATLAS experiment during Run 1 of the LHC. The studies presented focus on data taken during 2012 at a centre-of-mass energy of s√=8 TeV. The performance has been measured as a function of the number of interactions per bunch crossing over a wide range, from one to seventy. The measurement of the position and size of the luminous region and its use as a constraint to improve the primary vertex resolution are discussed. A longitudinal vertex position resolution of about 30 micrometers is achieved for events with high multiplicity of reconstructed tracks. The transverse position resolution is better than 20 micrometers and is dominated by the precision on the size of the luminous region. An analytical model is proposed to describe the primary vertex reconstruction efficiency as a function of the number of interactions per bunch crossing and of the longitudinal size of the luminous region. Agreement between the data and the predictions of this model is better than 3% up to seventy interactions per bunch crossing.
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    Search for new phenomena in events containing a same-flavour opposite-sign dilepton pair, jets, and large missing transverse momentum in s√=13 TeV pp collisions with the ATLAS detector
    (Springer Nature, 2017) Chan, Stephen; Clark, Brian Lee; Franklin, Melissa; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Roloff, Jennifer; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Zambito, Stefano
    Two searches for new phenomena in final states containing a same-flavour opposite-lepton (electron or muon) pair, jets, and large missing transverse momentum are presented. These searches make use of proton--proton collision data, collected during 2015 and 2016 at a centre-of-mass energy s√=13 TeV by the ATLAS detector at the Large Hadron Collider, which correspond to an integrated luminosity of 14.7 fb−1. Both searches target the pair production of supersymmetric particles, squarks or gluinos, which decay to final states containing a same-flavour opposite-sign lepton pair via one of two mechanisms: a leptonically decaying Z boson in the final state, leading to a peak in the dilepton invariant-mass distribution around the Z boson mass; and decays of neutralinos (e.g. χ̃ 02→ℓ+ℓ−χ̃ 01), yielding a kinematic endpoint in the dilepton invariant-mass spectrum. The data are found to be consistent with the Standard Model expectation. Results are interpreted in simplified models of gluino-pair (squark-pair) production, and provide sensitivity to gluinos (squarks) with masses as large as 1.70 TeV (980 GeV).
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    Measurement of the inclusive cross-sections of single top-quark and top-antiquark t-channel production in pp collisions at s=13$$ \sqrt{s}=13 $$ TeV with the ATLAS detector
    (Springer Nature, 2017) Franklin, Melissa; Huth, John; Morii, Masahiro; Chan, Stephen; Clark, Brian Lee; Giromini, Paolo; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Rogan, Christopher S.; Skottowe, Hugh Philip; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Yen, Andy; Zambito, Stefano
    A measurement of the t-channel single-top-quark and single-top-antiquark production crosssections in the lepton+jets channel is presented, using 3.2 fb−1 of proton–proton collision data at a centre-of-mass energy of 13 TeV, recorded with the ATLAS detector at the LHC in 2015. Events are selected by requiring one charged lepton (electron or muon), missing transverse momentum, and two jets with high transverse momentum, exactly one of which is required to be b-tagged. Using a binned maximum-likelihood fit to the discriminant distribution of a neural network, the cross-sections are determined to be σ(tq) = 156 ± 5 (stat.) ± 27 (syst.) ± 3 (lumi.) pb for single top-quark production and σ(tq¯ ) = 91 ± 4 (stat.) ± 18 (syst.) ± 2 (lumi.) pb for single top-antiquark production, assuming a top-quark mass of 172.5 GeV. The cross-section ratio is measured to be Rt = σ(tq)/σ(tq¯ ) = 1.72 ± 0.09 (stat.) ± 0.18 (syst.).
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    Luminosity Determination in Pp Collisions at S√s = 8 TeV Using the ATLAS Detector at the LHC
    (Springer Nature, 2016) Franklin, Melissa; Huth, John; Morii, Masahiro; Zambito, Stefano; Yen, Andy; Tuna, Alexander; Tong, Baojia; Tolley, Emma; Rogan, Christopher S.; Lazovich, Tomo; Ippolito, Valerio; Giromini, Paolo
    The luminosity determination for the ATLAS detector at the LHC during pp collisions at √s = 8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of δL/L = ±1.9% is obtained for the 22.7 fb−1 of pp collision data delivered to ATLAS at √s = 8 TeV in 2012.
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    Measurements of top-quark pair to Z-boson cross-section ratios at s√=13,8,7TeV with the ATLAS detector
    (Springer Nature, 2017) Chan, Stephen; Clark, Brian Lee; Di Petrillo, Karri Folan; Franklin, Melissa; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Roloff, Jennifer; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Zambito, Stefano
    Ratios of top-quark pair to Z-boson cross sections measured from proton--proton collisions at the LHC centre-of-mass energies of s√=13TeV, 8TeV, and 7TeV are presented by the ATLAS Collaboration. Single ratios, at a given s√ for the two processes and at different s√ for each process, as well as double ratios of the two processes at different s√, are evaluated. The ratios are constructed using previously published ATLAS measurements of the tt⎯⎯ and Z-boson production cross sections, corrected to a common phase space where required, and a new analysis of Z→ℓ+ℓ− where ℓ=e,μ at s√=13TeV performed with data collected in 2015 with an integrated luminosity of 3.2fb−1. Correlations of systematic uncertainties are taken into account when evaluating the uncertainties in the ratios. The correlation model is also used to evaluate the combined cross section of the Z→e+e− and the Z→μ+μ− channels for each s√ value. The results are compared to calculations performed at next-to-next-to-leading-order accuracy using recent sets of parton distribution functions. The data demonstrate significant power to constrain the gluon distribution function for the Bjorken-x values near 0.1 and the light-quark sea for x<0.02.
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    Measurement of the prompt J/ψ pair production cross-section in pp collisions at √s=8 TeV with the ATLAS detector
    (Springer Nature, 2017) Chan, Stephen; Clark, Brian Lee; Franklin, Melissa; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Roloff, Jennifer; Skottowe, Hugh Philip; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Zambito, Stefano
    The production of two prompt J/ψ mesons, each with transverse momenta pT>8.5 GeV and rapidity |y|<2.1, is studied using a sample of proton-proton collisions at √s=8 TeV, corresponding to an integrated luminosity of 11.4 fb−1 collected in 2012 with the ATLAS detector at the LHC. The differential cross-section, assuming unpolarised J/ψ production, is measured as a function of the transverse momentum of the lower-pT J/ψ meson, di-J/ψpT and mass, the difference in rapidity between the two J/ψ mesons, and the azimuthal angle between the two J/ψ mesons. The fraction of prompt pair events due to double parton scattering is determined by studying kinematic correlations between the two J/ψ mesons. The total and double parton scattering cross-sections are compared with predictions. The effective cross-section of double parton scattering is measured to be σeff=6.3±1.6(stat)±1.0(syst) mb.
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    Performance of the ATLAS trigger system in 2015
    (Springer Nature, 2017) Chan, Stephen; Clark, Brian Lee; Franklin, Melissa; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Roloff, Jennifer; Sun, Siyuan; Tolley, Emma; Tong, Baojia; Tuna, Alexander
    During 2015 the ATLAS experiment recorded 3.8 fb−1 of proton--proton collision data at a centre-of-mass energy of 13 TeV. The ATLAS trigger system is a crucial component of the experiment, responsible for selecting events of interest at a recording rate of approximately 1 kHz from up to 40 MHz of collisions. This paper presents a short overview of the changes to the trigger and data acquisition systems during the first long shutdown of the LHC and shows the performance of the trigger system and its components based on the 2015 proton--proton collision data.
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    High-ET isolated-photon plus jets production in pp collisions at s√= 8 TeV with the ATLAS detector
    (Elsevier BV, 2017) Franklin, Melissa; Chan, Stephen; Clark, Brian Lee; Giromini, Paolo; Huth, John; Ippolito, Valerio; Lazovich, Tomo; Lopez Mateos, David; Morii, Masahiro; Rogan, Christopher S.; Roloff, Jennifer; Tolley, Emma; Tong, Baojia; Tuna, Alexander; Zambito, Stefano
    The dynamics of isolated-photon plus one-, two- and three-jet production in pp collisions at a centre-of-mass energy of 8 TeV are studied with the ATLAS detector at the LHC using a data set with an integrated luminosity of 20.2 fb−1. Measurements of isolated-photon plus jets cross sections are presented as functions of the photon and jet transverse momenta. The cross sections as functions of the azimuthal angle between the photon and the jets, the azimuthal angle between the jets, the photon-jet invariant mass and the scattering angle in the photon-jet centre-of-mass system are presented. The pattern of QCD radiation around the photon and the leading jet is investigated by measuring jet production in an annular region centred on each object; enhancements are observed around the leading jet with respect to the photon in the directions towards the beams. The experimental measurements are compared to several different theoretical calculations, and overall a good description of the data is found.