We study parton energy-momentum exchange with the quark gluon plasma (QGP) within a multistage approach composed of in-medium Dokshitzer-Gribov-Lipatov-Altarelli-Parisi evolution at high virtuality, ...and (linearized) Boltzmann transport formalism at lower virtuality. This multistage simulation is then calibrated in comparison with high- p T charged hadrons, D mesons, and the inclusive jet nuclear modification factors, using Bayesian model-to-data comparison, to extract the virtuality-dependent transverse momentum broadening transport coefficient q ̂ . To facilitate this undertaking, we develop a quantitative metric for validating the Bayesian workflow, which is used to analyze the sensitivity of various model parameters to individual observables. The usefulness of this new metric in improving Bayesian model emulation is shown to be highly beneficial for future such analyses. Published by the American Physical Society 2024
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
A search for a long-lived, heavy neutral lepton ( N ) in 139 fb −1 of √s=13 TeV pp collision data collected by the ATLAS detector at the Large Hadron Collider is reported. The N is produced via W→ ...Nμ or W→ Ne and decays into two charged leptons and a neutrino, forming a displaced vertex. The N mass is used to discriminate between signal and background. No signal is observed, and limits are set on the squared mixing parameters of the N with the left-handed neutrino states for the N mass range 3 GeV< m N <15 GeV. For the first time, limits are given for both single-flavor and multiflavor mixing scenarios motivated by neutrino flavor oscillation results for both the normal and inverted neutrino-mass hierarchies.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UL, UM
A measurement of the top quark pair-production cross section in the lepton+jets decay channel is presented. It is based on 4.6 fb−1 of √s=7 TeV pp collision data collected during 2011 by the ATLAS ...experiment at the CERN Large Hadron Collider. A three-class, multidimensional event classifier based on support vector machines is used to differentiate t¯t events from backgrounds. The t¯t production cross section is found to be σt¯t=168.5±0.7(stat) +6.2−5.9(syst) +3.4−3.2(lumi) pb. The result is consistent with the Standard Model prediction based on QCD calculations at next-to-next-to-leading order.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
Jet production rates are measured in p+p and d+Au collisions at ...GeV recorded in 2008 with the PHENIX detector at the Relativistic Heavy Ion Collider. Jets are reconstructed using the R=0.3 anti-k ...sub(t) algorithm from energy deposits in the electromagnetic calorimeter and charged tracks in multiwire proportional chambers, and the jet transverse momentum (pT) spectra are corrected for the detector response. Spectra are reported for jets with 12<pT<50GeV/c, within a pseudorapidity acceptance of eta<0.3 . The nuclear-modification factor (R sub(dAu)) values for 0%-100% d+Au events are found to be consistent with unity, constraining the role of initial state effects on jet production. However, the centrality-selected R sub(dAu) values and central-to-peripheral ratios (R sub(CP)) show large, pT-dependent deviations from unity, challenging the conventional models that relate hard-process rates and soft-particle production in collisions involving nuclei.
Full text
Available for:
CMK, CTK, FMFMET, IJS, NUK, PNG, UM
A search for pair production of third-generation scalar leptoquarks decaying into a top quark and a τ-lepton is presented. The search is based on a dataset of pp collisions at $$ \sqrt{s} $$ s = 13 ...TeV recorded with the ATLAS detector during Run 2 of the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb-1. Events are selected if they have one light lepton (electron or muon) and at least one hadronically decaying τ -lepton, or at least two light leptons. In addition, two or more jets, at least one of which must be identified as containing b-hadrons, are required. Six final states, defined by the multiplicity and flavour of lepton candidates, are considered in the analysis. Each of them is split into multiple event categories to simultaneously search for the signal and constrain several leading backgrounds. The signal-rich event categories require at least one hadronically decaying τ-lepton candidate and exploit the presence of energetic final-state objects, which is characteristic of signal events. No significant excess above the Standard Model expectation is observed in any of the considered event categories, and 95% CL upper limits are set on the production cross section as a function of the leptoquark mass, for different assumptions about the branching fractions into tτ and bν. Scalar leptoquarks decaying exclusively into tτ are excluded up to masses of 1.43 TeV while, for a branching fraction of 50% into tτ, the lower mass limit is 1.22 TeV.
A search for charged Higgs bosons decaying into a top quark and a bottom quark is presented. The data analysed correspond to 139 fb-1 of proton-proton collisions at $$ \sqrt{s} $$ s = 13 TeV, ...recorded with the ATLAS detector at the LHC. The production of a heavy charged Higgs boson in association with a top quark and a bottom quark, pp → tbH+ → tbtb, is explored in the H+ mass range from 200 to 2000 GeV using final states with jets and one electron or muon. Events are categorised according to the multiplicity of jets and b-tagged jets, and multivariate analysis techniques are used to discriminate between signal and background events. No significant excess above the background-only hypothesis is observed and exclusion limits are derived for the production cross-section times branching ratio of a charged Higgs boson as a function of its mass; they range from 3.6 pb at 200 GeV to 0.036 pb at 2000 GeV at 95% confidence level. The results are interpreted in the hMSSM and $$ {M}_h^{125} $$ M h 125 scenarios.
A search for charged Higgs bosons decaying into W±W± or W±Z bosons is performed, involving experimental signatures with two leptons of the same charge, or three or four leptons with a variety of ...charge combinations, missing transverse momentum and jets. A data sample of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider between 2015 and 2018 is used. The data correspond to a total integrated luminosity of 139 fb-1. The search is guided by a type-II seesaw model that extends the scalar sector of the Standard Model with a scalar triplet, leading to a phenomenology that includes doubly and singly charged Higgs bosons. Two scenarios are explored, corresponding to the pair production of doubly charged H±± bosons, or the associated production of a doubly charged H±± boson and a singly charged H± boson. No significant deviations from the Standard Model predictions are observed. H±± bosons are excluded at 95% confidence level up to 350 GeV and 230 GeV for the pair and associated production modes, respectively.
PDF
