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  • 151.
    Derendarz, Dominik
    et al.
    PAS, Inst Nucl Phys, Ul Radzikowskiego 152, PL-31342 Krakow, Poland..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Measurement of the flow harmonic correlations in pp, p plus Pb and low multiplicity Pb plus Pb collisions with the ATLAS detector at the LHC2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 479-482Article in journal (Refereed)
    Abstract [en]

    Recent measurements of the correlations between flow harmonics obtained using four-particle symmetric cumulants and three-particle asymmetric cumulants with the ATLAS detector at the LHC are described. The data sets of pp, p+Pb and peripheral Pb+Pb collisions at various energies are analyzed, aiming to probe the long-range collective nature of multi-particle production in small systems. The sensitivity of the standard cumulant method to non-flow correlations is investigated by introducing the subevents method. A systematic reduction of non-flow effects is observed when using the two-subevent method. Further reduction is observed with the three-subevent method that is consistent with the results obtained with the four-subevent one. A negative correlation between v(2) and v(3) and a positive correlation between v(2) and v(4), for all studied collision systems and over full multiplicity range, is observed. The correlation strength computed as symmetric cumulants normalized by the < v(n)(2)> is similar for all collision systems and weakly depends on multiplicity. These measurements provide new evidence for long-range multi-particle collectivity in small collision systems and quantify the nature of its event-by-event fluctuations.

  • 152.
    Grabowska-Bold, Iwona
    et al.
    AGH Univ Sci & Technol, Krakow, Poland..
    Grabowska-Bold, I
    AGH Univ Sci & Technol, Fac Phys & Appl Comp Sci, Krakow, Poland..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Highlights from the ATLAS experiment2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 8-14Article in journal (Refereed)
    Abstract [en]

    This report provides an overview of the new results obtained by the ATLAS Collaboration at the LHC, which were presented at the Quark Matter 2018 conference. These measurements were covered in 12 parallel talks, one flash talk and 11 posters. In this document, a discussion of results is grouped into four areas: electromagnetic interactions, jet quenching, quarkonia and heavy-flavour production, and collectivity in small and larger systems. Measurements from the xenon-xenon collisions based on a short run collected in October 2017 are reported for the first time.

  • 153.
    Hu, Qipeng
    et al.
    Brookhaven Natl Lab, Upton, NY 11973 USA..
    Lund-Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Measurement of heavy flavor production and azimuthal anisotropy in small and large systems with ATLAS2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 687-690Article in journal (Refereed)
    Abstract [en]

    Heavy-flavor hadron production and collective motion in A+A collisions provide insight into the energy loss mechanism and transport properties of heavy quarks in the QGP. The same measurements in p+A collisions serve as an important baseline for understanding the observations in A+A collisions. For example, detailed studies of heavy-flavor hadron azimuthal anisotropy in p+A collisions may help to address whether the observed long-range "ridge" correlation arises from hard or semi-hard processes, or if it is the result of mechanisms unrelated to the initial hardness scale. These proceedings summarize heavy-flavor hadron production, via their semi-leptonic decay to muons in 2.76 TeV Pb+Pb and pp collisions, non-prompt J/psi in 5.02 TeV Pb+Pb and pp collisions, and prompt D-0 mesons in 8.16 TeV p+Pb collisions using ATLAS detector at the LHC. Azimuthal anisotropy of heavy-flavor hadrons is studied via their decay muons in 2.76 TeV Pb+Pb and 8.16 TeV p+Pb collisions, and via non-prompt J/psi in 5.02 TeV Pb+Pb collisions. Strong suppression of heavy-flavor hadron production and azimuthal anisotropy are observed in Pb+Pb collisions, while significant azimuthal anisotropy of heavy-flavor muons is observed in p+Pb collisions, without evidence of the modification of their production rates.

  • 154.
    Lee, Lawrence
    et al.
    Harvard Univ, Lab Particle Phys & Cosmol, Cambridge, MA 02138 USA..
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Suffer, Abner
    Yu, Tien-Tien
    Collider searches for long-lived particles beyond the Standard Model2019In: Progress in Particle and Nuclear Physics, ISSN 0146-6410, Vol. 106, p. 210-255Article, review/survey (Refereed)
    Abstract [en]

    Despite decades of attempts to reveal its flaws, the Standard Model of particle physics (SM) has withstood all experimental tests and its predictions are in excellent agreement with data. Since the theory was formulated, experiments have provided little guidance regarding the explanations of phenomena not described by the SM, such as the baryon asymmetry of the universe and dark matter. Nor do we have satisfying understanding of the aesthetic and theoretical problems of the model, despite years of searching for new processes and particles proposed to solve them. Such particles can evade being discovered by the comprehensive search programs at collider experiments if the analysis selections and the algorithms used to reconstruct the detector data are not matched to the characteristics of the particles, e.g. if they have long enough lifetimes. As interest in searches for such long-lived particles at colliders grows rapidly, we present a review of this area of research in this article. The broad range of theoretical motivations for particles with long lifetimes and the experimental strategies and methods employed to search for them are described. Results from decades of searches are reviewed, as are opportunities for the next generation of searches both at existing and proposed future experiments. 

  • 155.
    Perepelitsa, Dennis, V
    et al.
    Univ Colorado, Boulder, CO 80309 USA..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Photon-tagged measurements of jet quenching with ATLAS2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 595-598Article in journal (Refereed)
    Abstract [en]

    Events containing a high transverse momentum (p(T)) prompt photon offer a useful way to study the dynamics of the hot, dense medium produced in heavy ion collisions. Because photons do not carry color charge, they are unaffected by the medium, and thus provide information about the momentum, direction, and flavor (quark or gluon) of the associated hard-scattered parton before it begins to shower and become quenched. In particular, the presence of a high-p(T) photon can be used to select pp and Pb+Pb events with the same configuration before quenching, limiting the effects of quenching-induced selection biases present in other jet measurements. The large statistics pp and Pb+Pb data delivered by the LHC in 2015 allow for a detailed study of photon-tagged jet quenching effects, such as the overall parton energy loss and modified structure of the component of the shower which remains correlated with the initial parton direction (e.g. in cone). In this proceeding, photon-tagged measurements of jet quenching by ATLAS are reported.

  • 156.
    Puri, Akshat
    et al.
    Univ Illinois, Champaign, IL 61820 USA..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Measurement of angular and momentum distributions of charged particles within and around jets in Pb plus Pb and pp collisions at root s(NN)=5.02 TeV with ATLAS at the LHC2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 177-179Article in journal (Refereed)
    Abstract [en]

    Studies of the fragmentation of jets into charged particles in heavy-ion collisions can help in understanding the mechanism of jet quenching by the hot and dense QCD matter created in such collisions, the quark-gluon plasma. These proceedings present a measurement of the angular distribution of charged particles around the jet axis in root s(NN) = 5.02 TeV Pb+Pb and pp collisions, done using the ATLAS detector at the LHC. The measurement is performed inside jets reconstructed with the anti-k(t) algorithm with radius parameter R = 0.4, and is extended to regions outside the jet cone. Results are presented as a function of Pb+Pb collision centrality, and both jet and charged-particle transverse momenta.

  • 157.
    Spousta, Martin
    et al.
    Charles Univ Prague, Fac Math & Phys, V Holesovickach 2, Prague 18000, Czech Republic..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Jet suppression and jet substructure in Pb plus Pb and Xe plus Xe collisions with the ATLAS detector2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 611-614Article in journal (Refereed)
    Abstract [en]

    This short summary presents latest measurements of the nuclear modification factor, R-AA, for R = 0.4 jets in Pb+Pb collisions at root s(NN) = 5.02 TeV with the ATLAS detector at the LHC. The analysis is performed over a large range of transverse momentum, up to p(T) = 1 TeV, and differentially in jet p(T), rapidity, and collision centrality. The jet R-AA is measured also differentially in the jet mass, m, which provides new information on the dependence of the energy loss on the substructure of jets. Latest results by ATLAS on the dijet momentum balance in Xe+Xe collisions at root s(NN) = 5.44 TeV are presented and compared to the same quantity measured in Pb+Pb collisions at root s(NN) = 5.02 TeV. These recent measurements should help us understand mechanisms of parton energy loss and properties of hot and dense matter created in heavy-ion collisions.

  • 158.
    Steinberg, Peter
    et al.
    Brookhaven Natl Lab, Upton, NY 11973 USA.;Brookhaven Natl Lab, Phys Dept, Upton, NY USA..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Royal Inst Technol, Phys Dept, Stockholm, Sweden..
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    et al.,
    Electromagnetic processes with quasireal photons in Pb plus Pb collisions: QED, QCD, and the QGP2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 259-262Article in journal (Refereed)
    Abstract [en]

    Electromagnetic processes, both photon-photon and photon-nucleus, are shown to be useful in studying aspects of QED, QCD, and potentially the QGP. Using lead-lead collisions at root s(NN) = 5.02 TeV, the ATLAS detector has performed measurements of exclusive dimuon production, light-by-light scattering (via exclusive diphoton production), and photo-nuclear dijet production. These are all important examples of ultraperipheral collisions, where the nuclei do not interact hadronically. A recent study of the opening angles of dimuons produced in hadronic heavy-ion collisions, after subtracting heavy-flavor backgrounds, demonstrates that the dimuons carry information correlated with the overlap geometry, potentially about the density of charges in the QGP itself.

  • 159.
    Zhou, Mingliang
    et al.
    SUNY Stony Brook, Dept Chem, Stony Brook, NY 11794 USA..
    Jensen, Bengt
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ohm, Christian
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ripellino, Giulia
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Sidebo, P. Edvin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Strandberg, Jonas
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Zwalinski, L.
    CERN, Geneva, Switzerland..
    Flow fluctuations in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector2019In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, p. 323-326Article in journal (Refereed)
    Abstract [en]

    Measurements of four-particle cumulants c(n){4} for n = 1, 2, 3, 4 are presented using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02 TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of single harmonics p(v(n)). For the first time, a negative c(1){4} is observed. The c(4){4} is found to be negative in central collisions but changes sign around 20-25% centrality. This behavior is consistent with a nonlinear contribution to v(4) that is proportional to v(2)(2). c(2){4} and c(3){4} are calculated using two reference event classes in order to investigate the influence of volume fluctuations. Over most of the centrality range, c(2){4} and c(3){4} are found to be negative, while in the ultra-central collisions, c(2){4} changes sign and becomes positive, suggesting a deviation from Gaussian behavior in the event-by-event fluctuation of v(2). The magnitudes of the sign change are also found to be dependent of the event class definition .

1234 151 - 159 of 159
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