Browsing by Subject "530"

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    Charged-particle distributions in √s=13 TeV pp interactions measured with the ATLAS detector at the LHC
    (2016) Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Abeloos, B; Aben, R; Abolins, M; AbouZeid, O S; Abraham, N L; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Agricola, J; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S
    Charged-particle distributions are measured in proton–proton collisions at a centre-of-mass energy of 13 TeV, using a data sample of nearly 9 million events, corresponding to an integrated luminosity of 170 μb−1, recorded by the ATLAS detector during a special Large Hadron Collider fill. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on the charged-particle multiplicity are presented. The measurements are performed with charged particles with transverse momentum greater than 500 MeV and absolute pseudorapidity less than 2.5, in events with at least one charged particle satisfying these kinematic requirements. Additional measurements in a reduced phase space with absolute pseudorapidity less than 0.8 are also presented, in order to compare with other experiments. The results are corrected for detector effects, presented as particle-level distributions and are compared to the predictions of various Monte Carlo event generators.
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    High-ET isolated-photon plus jets production in pp collisions at √s = 8 TeV with the ATLAS detector
    (2017) Aaboud, M; Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Abeloos, B; AbouZeid, O S; Abraham, N L; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adachi, S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S; Alconada Verzini, M J
    Available online at www.sciencedirect.com ScienceDirect Nuclear Physics B 918 (2017) 257–316 www.elsevier.com/locate/nuclphysb High-E T isolated-photon plus jets production in pp collisions at s = 8 TeV with the ATLAS detector .The ATLAS Collaboration Received 21 November 2016; received in revised form 3 March 2017; accepted 6 March 2017 Available online 11 March 2017 Editor: Valerie Gibson Abstract 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 func- tions 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 cen- tred 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. © 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP 3 . 1. Introduction The production of prompt photons in association with jets in proton–proton collisions, pp → γ + jets + X, provides a testing ground for perturbative QCD (pQCD) with a hard colour- less probe less affected by hadronisation effects than jet production. The measurements of the angular correlations between the photon and the jets can be used to probe the dynamics of the hard-scattering process. Since the dominant production mechanism in pp collisions at the Large Hadron Collider (LHC) proceeds via the qg → qγ process, measurements of prompt-photon plus jet production are useful in constraining the gluon density in the proton [1,2]. These mea- E-mail address: atlas.publications@cern.ch. http://dx.doi.org/10.1016/j.nuclphysb.2017.03.006 0550-3213/© 2017 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP 3 .
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    Measurement of W + W − production in association with one jet in proton–proton collisions at s = 8 TeV with the ATLAS detector
    (2016) Aaboud, M; Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Abeloos, B; Aben, R; AbouZeid, O S; Abraham, N L; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adachi, S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S
    The production of W boson pairs in association with one jet in pp collisions at View the MathML source is studied using data corresponding to an integrated luminosity of 20.3 fb−1 collected by the ATLAS detector during 2012 at the CERN Large Hadron Collider. The cross section is measured in a fiducial phase-space region defined by the presence of exactly one electron and one muon, missing transverse momentum and exactly one jet with a transverse momentum above 25 GeV and a pseudorapidity of η <4.5. The leptons are required to have opposite electric charge and to pass transverse momentum and pseudorapidity requirements. The fiducial cross section is found to be View the MathML source. In combination with a previous measurement restricted to leptonic final states with no associated jets, the fiducial cross section of WW production with zero or one jet is measured to be View the MathML source. The ratio of fiducial cross sections in final states with one and zero jets is determined to be 0.36±0.05. Finally, a total cross section extrapolated from the fiducial measurement of WW production with zero or one associated jet is reported. The measurements are compared to theoretical predictions and found in good agreement.
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    Measurement of the charge asymmetry in highly boosted top-quark pair production in √s = 8 TeV pp collision data collected by the ATLAS experiment
    (2016) Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Abeloos, B; Aben, R; Abolins, M; AbouZeid, O S; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Agricola, J; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S; Alconada Verzini, M J
    In the pp → tt¯ process the angular distributions of top and anti-top quarks are expected to present a subtle difference, which could be enhanced by processes not included in the Standard Model. This Letter presents a measurement of the charge asymmetry in events where the top-quark pair is produced with a large invariant mass. The analysis is performed on 20.3 fb−1 of pp collision data at √s = 8 TeV collected by the ATLAS experiment at the LHC, using reconstruction techniques specifically designed for the decay topology of highly boosted top quarks. The charge asymmetry in a fiducial region with large invariant mass of the top-quark pair (mtt¯ > 0.75 TeV) and an absolute rapidity difference of the top and anti-top quark candidates within −2 < |yt| − |yt¯| < 2 is measured to be 4.2 ± 3.2%, in agreement with the Standard Model prediction at next-to-leading order. A differential measurement in three tt¯ mass bins is also presented.
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    Measurement of the dependence of transverse energy production at large pseudorapidity on the hard-scattering kinematics of proton–proton collisions at √s = 2.76 TeV with ATLAS
    (2016) Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Aben, R; Abolins, M; AbouZeid, O S; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Agricola, J; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S; Alconada Verzini, M J; Aleksa, M
    The relationship between jet production in the central region and the underlying-event activity in a pseudorapidity-separated region is studied in 4.0 pb -1 of √s = 2.76 TeV pp collision data recorded with the ATLAS detector at the LHC. The underlying event is characterised through measurements of the average value of the sum of the transverse energy at large pseudorapidity downstream of one of the protons, which are reported here as a function of hard-scattering kinematic variables. The hard scattering is characterised by the average transverse momentum and pseudorapidity of the two highest transverse momentum jets in the event. The dijet kinematics are used to estimate, on an event-by-event basis, the scaled longitudinal momenta of the hard-scattered partons in the target and projectile beam-protons moving toward and away from the region measuring transverse energy, respectively. Transverse energy production at large pseudorapidity is observed to decrease with a linear dependence on the longitudinal momentum fraction in the target proton and to depend only weakly on that in the projectile proton. Lastly, the results are compared to the predictions of various Monte Carlo event generators, which qualitatively reproduce the trends observed in data but generally underpredict the overall level of transverse energymore » at forward pseudorapidity.« less
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    Measurement of transverse energy–energy correlations in multi-jet events in pp collisions at √s = 7 TeV using the ATLAS detector and determination of the strong coupling constant αs(mZ )
    (2015) Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Aben, R; Abolins, M; AbouZeid, O S; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Agricola, J; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S; Alconada Verzini, M J; Aleksa, M
    High transverse momentum jets produced in pp collisions at a centre of mass energy of 7 TeV are used to measure the transverse energy–energy correlation function and its associated azimuthal asymmetry. The data were recorded with the ATLAS detector at the LHC in the year 2011 and correspond to an integrated luminosity of 158 pb−1. The selection criteria demand the average transverse momentum of the two leading jets in an event to be larger than 250 GeV. The data at detector level are well described by Monte Carlo event generators. They are unfolded to the particle level and compared with theoretical calculations at next-to-leading-order accuracy. The agreement between data and theory is good and provides a precision test of perturbative Quantum Chromodynamics at large momentum transfers. From this comparison, the strong coupling constant given at the Z boson mass is determined to be αs(mZ ) = 0.1173 ± 0.0010 (exp.) +0.0065 −0.0026 (theo.).
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    Measurements of the charge asymmetry in top-quark pair production in the dilepton final state at √s = 8 TeV with the ATLAS detector
    (2016) Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Abeloos, B; Aben, R; Abolins, M; AbouZeid, O S; Abraham, N L; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Agricola, J; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S
    Measurements of the top--antitop quark pair production charge asymmetry in the dilepton channel are presented using data corresponding to an integrated luminosity of $20.3$ $textrm{fb}{-1}$ from $pp$ collisions at a center-of-mass energy of $sqrt{s} = 8$ TeV collected with the ATLAS detector at the Large Hadron Collider at CERN. Inclusive and differential measurements as a function of the invariant mass, transverse momentum, and longitudinal boost of the $tbar{t}$ system are performed both in the full phase space and in a fiducial phase space closely matching the detector acceptance. Two observables are studied: $A{ellell}_{textrm{C}}$ based on the selected leptons and $A{tbar{t}}_{textrm{C}}$ based on the reconstructed $tbar{t}$ final state. The inclusive asymmetries are measured in the full phase space to be $A{ellell}_{textrm{C}} = 0.008 pm 0.006$ and $A{tbar{t}}_{textrm{C}} = 0.021 pm 0.016$, which are in agreement with the Standard Model predictions of $A{ellell}_{textrm{C}} = 0.0064 pm 0.0003 $ and $A{tbar{t}}_{textrm{C}} = 0.0111 pm 0.0004$.
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    Measurements of W Z production cross sections in pp collisions at √s = 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings
    (2016) Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Abeloos, B; Aben, R; Abolins, M; AbouZeid, O S; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Agricola, J; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S; Alconada Verzini, M J
    PHYSICAL REVIEW D 93, 092004 (2016) Measurements W±Z production cross sections in pp collisions at s = 8 TeV with the ATLAS detector and limits on anomalous gauge boson self-couplings G. Aad et al. * (ATLAS Collaboration) (Received 8 March 2016; published 13 May 2016) This paper presents measurements of W Z production in pp collisions at a center-of-mass energy of 8 TeV. The gauge bosons are reconstructed using their leptonic decay modes into electrons and muons. The data were collected in 2012 by the ATLAS experiment at the Large Hadron Collider and correspond to an integrated luminosity of 20.3 fb −1 . The measured inclusive cross section in the detector fiducial region is σ W Z→l 0 νll ¼ 35.1 0.9ðstatÞ 0.8ðsysÞ 0.8ðlumiÞ fb, for one leptonic decay channel. In comparison, the next-to-leading-order Standard Model expectation is 30.0 2.1 fb. Cross sections for W þ Z and W − Z production and their ratio are presented as well as differential cross sections for several kinematic observables. Limits on anomalous triple gauge boson couplings are derived from the transverse mass spectrum of the W Z system. From the analysis of events with a W and a Z boson associated with two or more forward jets an upper limit at 95% confidence level on the W Z scattering cross section of 0.63 fb, for each leptonic decay channel, is established, while the Standard Model prediction at next-to-leading order is 0.13 0.01 fb. Limits on anomalous quartic gauge boson couplings are also extracted. DOI: 10.1103/PhysRevD.93.092004 I. INTRODUCTION The study of W Z diboson production is an important test of the Standard Model (SM) for its sensitivity to the gauge boson self-interactions, related to the non-Abelian structure of the electroweak interaction. It provides the means to investigate vector boson scattering (VBS) proc- esses, which directly probe the electroweak symmetry breaking sector of the SM, and to extract constraints on anomalous triple and quartic gauge boson couplings (aTGC and aQGC). Improved constraints can probe scales of new physics in the multi-TeV range and provide a way to look for signals of new physics in a model- independent way. Precise measurements of W Z production will also help to improve the existing QCD calculations of this process. This paper presents measurements of the W Z produc- tion cross section and limits on the aTGC and aQGC obtained by analyzing proton-proton (pp) collisions at a p ffiffiffi center-of-mass energy of s ¼ 8 TeV. The leptonic decay modes of the W and Z bosons are used and all quoted fiducial production cross sections include the branching ratio of the gauge bosons into channels with electrons or muons. The analyzed data sample was collected in 2012 by the ATLAS experiment at the Large Hadron Collider Full author list given at the end of the article. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distri- bution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. (LHC), and corresponds to an integrated luminosity of 20.3 fb −1 . Experimentally, W Z production has the ad- vantage of a higher cross section than ZZ production. At the same time, with three charged leptons and the require- ment that two of them originate from a Z boson, the leptonic W Z final states are easier to discriminate from the background than the leptonic WW final states. Measurements of the W Z production cross section have been reported in proton-antiproton collisions at a center- p ffiffiffi of-mass energy of s ¼ 1.96 TeV by the CDF and D0 collaborations [1,2] using integrated luminosities of p ffiffiffi 7.1 fb −1 and 8.6 fb −1 , respectively, and for s ¼ 7 TeV proton-proton collisions, using an integrated luminosity of 4.6 fb −1 , by the ATLAS Collaboration [3]. Limits on anomalous charged-current gauge couplings were also reported previously by the LEP, Tevatron, and LHC experi- ments [4–6]. In hadron collisions, the selection of W Z final states allows direct access to the WWZ gauge coupling without the need of disentangling it from the WWγ gauge coupling as in W W ∓ events from hadronic or e þ e − collisions. Compared to the previously published measurements, this paper uses data collected at a higher center-of-mass energy with a fourfold increase in integrated luminosity and presents additional measurements. The production cross section is measured in a fiducial phase space inclusively and as single differential cross sections as a function of each of several kinematic variables: the transverse momen- tum p T of the W and Z bosons, the jet multiplicity, the transverse mass of the WZ system, m WZ T , and the p T of the neutrino associated with the W boson decay. An interesting © 2016 CERN, for the ATLAS Collaboration
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    Search for heavy long-lived charged R-hadrons with the ATLAS detector in 3.2 fb−1of proton–proton collision data at √s=13 TeV
    (2016) Aaboud, M; Aad, G; Abbott, B; Abdallah, J; Abdinov, O; Abeloos, B; Aben, R; AbouZeid, O S; Abraham, N L; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adersberger, M; Adomeit, S; Adye, T; Affolder, A A; Agatonovic-Jovin, T; Agricola, J; Aguilar-Saavedra, J A; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimov, A V; Alberghi, G L; Albert, J
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