Electromagnetic probes

We introduce the seminal developments in the theory and experiments of electromagnetic probes for the study of the dynamics of relativistic heavy ion collisions and quark gluon plasma.Comment: 47 pages, 33 Figures; Lectures delivered by Dinesh K. Srivastava at QGP Winter School (QGPWS08) at Jaipur, India, February 1-3, 200

Electromagnetic Probes

A review is presented of dilepton and real photon measurements in relativistic heavy ion collisions over a very broad energy range from the low energies of the BEVALAC up to the highest energies available at RHIC. The dileptons cover the invariant mass range \mll = 0 - 2.5 GeV/c$^2$, i.e. the continuum at low and intermediate masses and the light vector mesons, $\rho, \omega, \phi$. The review includes also measurements of the light vector mesons in elementary reactions.Comment: To be published in Landolt-Boernstein Volume 1-23A; 40 pages, 24 figures. Final version updated with small changes to the text, updated references and updated figure

Search for resonances decaying into a weak vector boson and a Higgs boson in the fully hadronic final state produced in proton-proton collisions at s =13 TeV with the ATLAS detector

Indexación ScopusA search for heavy resonances decaying into a W or Z boson and a Higgs boson produced in proton-proton collisions at the Large Hadron Collider at s=13 TeV is presented. The analysis utilizes the dominant W→qq¯′ or Z→qq¯ and H→bb¯ decays with substructure techniques applied to large-radius jets. A sample corresponding to an integrated luminosity of 139 fb-1 collected with the ATLAS detector is analyzed and no significant excess of data is observed over the background prediction. The results are interpreted in the context of the heavy vector triplet model with spin-1 W′ and Z′ bosons. Upper limits on the cross section are set for resonances with mass between 1.5 and 5.0 TeV, ranging from 6.8 to 0.53 fb for W′→WH and from 8.7 to 0.53 fb for Z′→ZH at the 95% confidence level. © 2020 CERN.https://journals-aps-org.recursosbiblioteca.unab.cl/prd/abstract/10.1103/PhysRevD.102.11200

Search for heavy diboson resonances in semileptonic final states in pp collisions at √s=13 TeV with the ATLAS detector

Indexación ScopusThis paper reports on a search for heavy resonances decaying into WW, ZZ or WZ using proton–proton collision data at a centre-of-mass energy of s=13 TeV. The data, corresponding to an integrated luminosity of 139 fb 1, were recorded with the ATLAS detector from 2015 to 2018 at the Large Hadron Collider. The search is performed for final states in which one W or Z boson decays leptonically, and the other W boson or Z boson decays hadronically. The data are found to be described well by expected backgrounds. Upper bounds on the production cross sections of heavy scalar, vector or tensor resonances are derived in the mass range 300–5000 GeV within the context of Standard Model extensions with warped extra dimensions or including a heavy vector triplet. Production through gluon–gluon fusion, Drell–Yan or vector-boson fusion are considered, depending on the assumed model. © 2020, CERN for the benefit of the ATLAS collaboration.https://link-springer-com.recursosbiblioteca.unab.cl/article/10.1140/epjc/s10052-020-08554-

Operation of the ATLAS trigger system in run 2

The ATLAS experiment at the Large Hadron Collider employs a two-level triggersystem to record data at an average rate of 1 kHz from physics collisions,starting from an initial bunch crossing rate of 40 MHz. During the LHC Run 2(2015-2018), the ATLAS trigger system operated successfully with excellentperformance and flexibility by adapting to the various run conditionsencountered and has been vital for the ATLAS Run-2 physics programme. Forproton-proton running, approximately 1500 individual event selections wereincluded in a trigger menu which specified the physics signatures and selectionalgorithms used for the data-taking, and the allocated event rate andbandwidth. The trigger menu must reflect the physics goals for a given datacollection period, taking into account the instantaneous luminosity of the LHCand limitations from the ATLAS detector readout, online processing farm, andoffline storage. This document discusses the operation of the ATLAS triggersystem during the nominal proton-proton data collection in Run 2 with examplesof special data-taking runs. Aspects of software validation, evolution of thetrigger selection algorithms during Run 2, monitoring of the trigger system anddata quality as well as trigger configuration are presented.Fil: Aad, G.. Aix-Marseille Université; FranciaFil: Abbott, B.. Oklahoma State University; Estados UnidosFil: Abbott, D.C.. University of Massachusetts; Estados UnidosFil: Abed Abud, A.. Cern - European Organization for Nuclear Research; SuizaFil: Abeling, K.. Georg-August-Universität Göttingen; AlemaniaFil: Abhayasinghe, D.K.. Royal Holloway University of London; Reino UnidoFil: Abidi, S. H.. University of Toronto; CanadáFil: AbouZeid, O. S.. Czech Academy of Sciences; República ChecaFil: Abraham, N. L.. University of Sussex; Reino UnidoFil: Abramowicz, H.. Universitat Tel Aviv; IsraelFil: Abreu, H.. Technion - Israel Institute of Technology; IsraelFil: Abreu, R.. University of Oregon; Estados UnidosFil: Abulaiti, Y.. Argonne National Laboratory; Estados UnidosFil: Acharya, B. S.. Istituto Nazionale di Fisica Nucleare; Italia. The Abdus Salam. International Centre for Theoretical Physics; ItaliaFil: Achkak, B.. Georg-August-Universität Göttingen; AlemaniaFil: Adam, L.. University of Montreal; CanadáFil: Adam Bourdarios, C.. Universite Grenoble Alpes; Francia. Université Savoie Mont Blanc; FranciaFil: Adamczyk, L.. AGH University of Science and Technology; PoloniaFil: Adamek, L.. University of Toronto; CanadáFil: Adelman, J.. Northern Illinois University; Estados UnidosFil: Adersberger, M.. Ludwig-Maximilians-Universität München; AlemaniaFil: Adiguzel, A.. Bogazici University; TurquíaFil: Adorni,S.. Université de Genève; SuizaFil: Adye, T.. Universite Paris-Saclay;Fil: Affolder, A. A.. University of California Santa Cruz; Estados UnidosFil: Afik, Y.. Technion - Israel Institute of Technology; IsraelFil: Agapopoulou, C.. Universite Paris-Saclay;Fil: Agaras, M. N.. Université Clermont Auvergne; Francia. Centre National de la Recherche Scientifique; FranciaFil: Aggarwal, A.. Radboud Universiteit Nijmegen; Países BajosFil: Orellana, Gonzalo Enrique. Universidad Nacional de La Plata. Facultad de Ciencias Exactas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Física La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Física La Plata; Argentin

Search for long-lived neutral particles produced in pp collisions at ffisffi p =13 TeV decaying into displaced hadronic jets in the ATLAS inner detector and muon spectrometer

A search is presented for pair production of long-lived neutral particles using 33 fb-1 of s=13 TeV proton-proton collision data, collected during 2016 by the ATLAS detector at the LHC. This search focuses on a topology in which one long-lived particle decays in the ATLAS inner detector and the other decays in the muon spectrometer. Special techniques are employed to reconstruct the displaced tracks and vertices in the inner detector and in the muon spectrometer. One event is observed that passes the full event selection, which is consistent with the estimated background. Limits are placed on scalar boson propagators with masses from 125 GeV to 1000 GeV decaying into pairs of long-lived hidden-sector scalars with masses from 8 GeV to 400 GeV. The limits placed on several low-mass scalars extend previous exclusion limits in the range of proper lifetimes cτ from 5 cm to 1 m. © 2020 CERN.Indexación: Scopu

Measurement of the Lund Jet Plane Using Charged Particles in 13 TeV Proton-Proton Collisions with the ATLAS Detector

The prevalence of hadronic jets at the LHC requires that a deep understanding of jet formation and structure is achieved in order to reach the highest levels of experimental and theoretical precision. There have been many measurements of jet substructure at the LHC and previous colliders, but the targeted observables mix physical effects from various origins. Based on a recent proposal to factorize physical effects, this Letter presents a double-differential cross-section measurement of the Lund jet plane using 139 fb-1 of s=13 TeV proton-proton collision data collected with the ATLAS detector using jets with transverse momentum above 675 GeV. The measurement uses charged particles to achieve a fine angular resolution and is corrected for acceptance and detector effects. Several parton shower Monte Carlo models are compared with the data. No single model is found to be in agreement with the measured data across the entire plane. © 2020 CERN.Indexacón:Scopu

Search for new resonances in mass distributions of jet pairs using 139 fb −1 of pp collisions at √s = 13 TeV with the ATLAS detector

A search for new resonances decaying into a pair of jets is reported using the dataset of proton-proton collisions recorded at s = 13 TeV with the ATLAS detector at the Large Hadron Collider between 2015 and 2018, corresponding to an integrated luminosity of 139 fb−1. The distribution of the invariant mass of the two leading jets is examined for local excesses above a data-derived estimate of the Standard Model background. In addition to an inclusive dijet search, events with jets identified as containing b-hadrons are examined specifically. No significant excess of events above the smoothly falling background spectra is observed. The results are used to set cross-section upper limits at 95% confidence level on a range of new physics scenarios. Model-independent limits on Gaussian-shaped signals are also reported. The analysis looking at jets containing b-hadrons benefits from improvements in the jet flavour identification at high transverse momentum, which increases its sensitivity relative to the previous analysis beyond that expected from the higher integrated luminosity. [Figure not available: see fulltext.] © 2020, The Author(s).Indexación: Scopu

Measurement of isolated-photon plus two-jet production in pp collisions at p s = 13TeV with the ATLAS detector

The dynamics of isolated-photon plus two-jet production in "padding-size-4-x display--inline-block" style="background: var(--highlight-yellow); color: inherit;">pp collisions at a centre-of-mass energy of 13 TeV are studied with the ATLAS detector at the LHC using a dataset corresponding to an integrated luminosity of 36.1 fb−1. Cross sections are measured as functions of a variety of observables, including angular correlations and invariant masses of the objects in the final state, γ + jet + jet. Measurements are also performed in phase-space regions enriched in each of the two underlying physical mechanisms, namely direct and fragmentation processes. The measurements cover the range of photon (jet) transverse momenta from 150 GeV (100 GeV) to 2 TeV. The tree-level plus parton-shower predictions from Sherpa and Pythia as well as the next-to-leading-order QCD predictions from Sherpa are compared with the measurements. The next-to-leading-order QCD predictions describe the data adequately in shape and normalisation except for regions of phase space such as those with high values of the invariant mass or rapidity separation of the two jets, where the predictions overestimate the data. [Figure not available: see fulltext.] © 2020, The Author(s).Indexación: Scopu

Search for Higgs boson production in association with a high-energy photon via vector-boson fusion with decay into bottom quark pairs at √s = 13 TeV with the ATLAS detector

Indexación ScopusA search is presented for the production of the Standard Model Higgs boson in association with a high-energy photon. With a focus on the vector-boson fusion process and the dominant Higgs boson decay into b-quark pairs, the search benefits from a large reduction of multijet background compared to more inclusive searches. Results are reported from the analysis of 132 fb−1 of pp collision data at s = 13 TeV collected with the ATLAS detector at the LHC. The measured Higgs boson signal yield in this final-state signature is 1.3 ± 1.0 times the Standard Model prediction. The observed significance of the Higgs boson signal above the background is 1.3 standard deviations, compared to an expected significance of 1.0 standard deviations. [Figure not available: see fulltext.] © 2021, The Author(s).https://link-springer-com.recursosbiblioteca.unab.cl/article/10.1007%2FJHEP03%282021%2926