Janusz Chwastowski
@ifj.edu.pl
professor; Department of Diffractive Processes/Division of Particle and Astroparticle Physics
The Henryk Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences/IFJ PAN
Scopus Publications
Scopus Publications
G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A. C. Abusleme Hoffman,et al.
Springer Science and Business Media LLC
AbstractSearches for the exclusive decays of Higgs and Z bosons into a vector quarkonium state and a photon are performed in the $$\\mu ^+\\mu ^-\\,\\gamma $$ μ + μ - γ final state with a proton–proton collision data sample corresponding to an integrated luminosity of 139 fb$$^{-1}$$ - 1 collected at $$\\sqrt{s}=13$$ s = 13 TeV with the ATLAS detector at the CERN Large Hadron Collider. The observed data are compatible with the expected backgrounds. The 95% confidence-level upper limits on the branching fractions of the Higgs boson decays into $$J/\\psi \\,\\gamma $$ J / ψ γ , $$\\psi (2S)\\,\\gamma $$ ψ ( 2 S ) γ , and $$\\Upsilon (1S,2S,3S)\\,\\gamma $$ Υ ( 1 S , 2 S , 3 S ) γ are found to be $$2.0\\times 10^{-4}$$ 2.0 × 10 - 4 , $$10.5\\times 10^{-4}$$ 10.5 × 10 - 4 , and $$(2.5,4.2,3.4)\\times 10^{-4}$$ ( 2.5 , 4.2 , 3.4 ) × 10 - 4 , respectively, assuming Standard Model production of the Higgs boson. The corresponding 95% CL upper limits on the branching fractions of the Z boson decays are $$1.2\\times 10^{-6}$$ 1.2 × 10 - 6 , $$2.4\\times 10^{-6}$$ 2.4 × 10 - 6 , and $$(1.1,1.3,2.4)\\times 10^{-6}$$ ( 1.1 , 1.3 , 2.4 ) × 10 - 6 . An observed 95% CL interval of $$(-133,175)$$ ( - 133 , 175 ) is obtained for the $$\\kappa _c/\\kappa _\\gamma $$ κ c / κ γ ratio of Higgs boson coupling modifiers, and a 95% CL interval of $$(-37,40)$$ ( - 37 , 40 ) is obtained for $$\\kappa _b/\\kappa _\\gamma $$ κ b / κ γ .
G. Aad, B. Abbott, D. C. Abbott, A. Abed Abud, K. Abeling, D. K. Abhayasinghe, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu,et al.
American Physical Society (APS)
A search for a long-lived, heavy neutral lepton (N) in 139 fb^{-1} of sqrt[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.
G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A. C. Abusleme Hoffman,et al.
American Physical Society (APS)
A test of CP invariance in Higgs boson production via vector-boson fusion has been performed in the H→γγ channel using 139 fb^{-1} of proton-proton collision data at sqrt[s]=13 TeV collected by the ATLAS detector at the LHC. The optimal observable method is used to probe the CP structure of interactions between the Higgs boson and electroweak gauge bosons, as described by an effective field theory. No sign of CP violation is observed in the data. Constraints are set on the parameters describing the strength of the CP-odd component in the coupling between the Higgs boson and the electroweak gauge bosons in two effective field theory bases: d[over ˜] in the HISZ basis and c_{HW[over ˜]} in the Warsaw basis. The results presented are the most stringent constraints on CP violation in the coupling between Higgs and weak bosons. The 95% C.L. constraint on d[over ˜] is derived for the first time and the 95% C.L. constraint on c_{HW[over ˜]} has been improved by a factor of 5 compared to the previous measurement.
G. Aad, B. Abbott, D.C. Abbott, K. Abeling, S.H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A.C. Abusleme Hoffman,et al.
Elsevier BV
G. Aad, B. Abbott, D.C. Abbott, K. Abeling, S.H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A.C. Abusleme Hoffman,et al.
Elsevier BV
G. Aad, B. Abbott, D.C. Abbott, K. Abeling, S.H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A.C. Abusleme Hoffman,et al.
Elsevier BV
G. Aad, B. Abbott, D.C. Abbott, K. Abeling, S.H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A.C. Abusleme Hoffman,et al.
Elsevier BV
G. Aad, B. Abbott, D.C. Abbott, K. Abeling, S.H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A.C. Abusleme Hoffman,et al.
Elsevier BV
G. Aad, B. Abbott, D.C. Abbott, A. Abed Abud, K. Abeling, D.K. Abhayasinghe, S.H. Abidi, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Elsevier BV
, G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract Inclusive and differential measurements of the top–antitop ($$ t\\overline{t} $$ t t ¯ ) charge asymmetry $$ {A}_{\\textrm{C}}^{t\\overline{t}} $$ A C t t ¯ and the leptonic asymmetry $$ {A}_{\\textrm{C}}^{\\ell \\overline{\\ell}} $$ A C ℓ ℓ ¯ are presented in proton–proton collisions at $$ \\sqrt{s} $$ s = 13 TeV recorded by the ATLAS experiment at the CERN Large Hadron Collider. The measurement uses the complete Run 2 dataset, corresponding to an integrated luminosity of 139 fb−1, combines data in the single-lepton and dilepton channels, and employs reconstruction techniques adapted to both the resolved and boosted topologies. A Bayesian unfolding procedure is performed to correct for detector resolution and acceptance effects. The combined inclusive $$ t\\overline{t} $$ t t ¯ charge asymmetry is measured to be $$ {A}_{\\textrm{C}}^{t\\overline{t}} $$ A C t t ¯ = 0.0068 ± 0.0015, which differs from zero by 4.7 standard deviations. Differential measurements are performed as a function of the invariant mass, transverse momentum and longitudinal boost of the $$ t\\overline{t} $$ t t ¯ system. Both the inclusive and differential measurements are found to be compatible with the Standard Model predictions, at next-to-next-to-leading order in quantum chromodynamics perturbation theory with next-to-leading-order electroweak corrections. The measurements are interpreted in the framework of the Standard Model effective field theory, placing competitive bounds on several Wilson coefficients.
G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A. C. Abusleme Hoffman,et al.
Springer Science and Business Media LLC
AbstractThe identification of b-jets, referred to as b-tagging, is an important part of many physics analyses in the ATLAS experiment at the Large Hadron Collider and an accurate calibration of its performance is essential for high-quality physics results. This publication describes the calibration of the light-flavour jet mistagging efficiency in a data sample of proton–proton collision events at $$\\sqrt{s}=13$$ s = 13 TeV corresponding to an integrated luminosity of 139 fb$$^{-1}$$ - 1 . The calibration is performed in a sample of Z bosons produced in association with jets. Due to the low mistagging efficiency for light-flavour jets, a method which uses modified versions of the b-tagging algorithms referred to as flip taggers is used in this work. A fit to the jet-flavour-sensitive secondary-vertex mass is performed to extract a scale factor from data, to correct the light-flavour jet mistagging efficiency in Monte Carlo simulations, while simultaneously correcting the b-jet efficiency. With this procedure, uncertainties coming from the modeling of jets from heavy-flavour hadrons are considerably lower than in previous calibrations of the mistagging scale factors, where they were dominant. The scale factors obtained in this calibration are consistent with unity within uncertainties.
G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A. C. Abusleme Hoffman,et al.
Springer Science and Business Media LLC
AbstractA search for pair-produced vector-like quarks using events with exactly one lepton (e or $$\\mu $$ μ ), at least four jets including at least one b-tagged jet, and large missing transverse momentum is presented. Data from proton–proton collisions at a centre-of-mass energy of $$\\sqrt{s}=$$ s = 13 $$\\text {TeV}$$ TeV , recorded by the ATLAS detector at the LHC from 2015 to 2018 and corresponding to an integrated luminosity of 139 fb$$^{-1}$$ - 1 , are analysed. Vector-like partners T and B of the top and bottom quarks are considered, as is a vector-like X with charge $$+5/3$$ + 5 / 3 , assuming their decay into a W, Z, or Higgs boson and a third-generation quark. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section of T and B quark pairs as a function of their mass are derived for various decay branching ratio scenarios. The strongest lower limits on the masses are 1.59 $$\\text {TeV}$$ TeV assuming mass-degenerate vector-like quarks and branching ratios corresponding to the weak-isospin doublet model, and 1.47 $$\\text {TeV}$$ TeV (1.46 $$\\text {TeV}$$ TeV ) for exclusive $$T \\rightarrow Zt$$ T → Z t ($$B/X \\rightarrow Wt$$ B / X → W t ) decays. In addition, lower limits on the T and B quark masses are derived for all possible branching ratios.
G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A. C. Abusleme Hoffman,et al.
Springer Science and Business Media LLC
AbstractThis paper presents a measurement of fiducial and differential cross-sections for $$W^{+}W^{-}$$ W + W - production in proton–proton collisions at $$\\sqrt{s}=13$$ s = 13 TeV with the ATLAS experiment at the Large Hadron Collider using a dataset corresponding to an integrated luminosity of 139 fb$$^{-1}$$ - 1 . Events with exactly one electron, one muon and no hadronic jets are studied. The fiducial region in which the measurements are performed is inspired by searches for the electroweak production of supersymmetric charginos decaying to two-lepton final states. The selected events have moderate values of missing transverse momentum and the ‘stransverse mass’ variable $$m_{\\textrm{T2}}$$ m T2 , which is widely used in searches for supersymmetry at the LHC. The ranges of these variables are chosen so that the acceptance is enhanced for direct $$W^{+}W^{-}$$ W + W - production and suppressed for production via top quarks, which is treated as a background. The fiducial cross-section and particle-level differential cross-sections for six variables are measured and compared with two theoretical SM predictions from perturbative QCD calculations.
, G. Aad, B. Abbott, K. Abeling, N. J. Abicht, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract A search for forward proton scattering in association with light-by-light scattering mediated by an axion-like particle is presented, using the ATLAS Forward Proton spectrometer to detect scattered protons and the central ATLAS detector to detect pairs of outgoing photons. Proton-proton collision data recorded in 2017 at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV were analysed, corresponding to an integrated luminosity of 14.6 fb−1. A total of 441 candidate events were selected. A search was made for a narrow resonance in the diphoton mass distribution, corresponding to an axion-like particle (ALP) with mass in the range 150–1600 GeV. No excess is observed above a smooth background. Upper limits on the production cross section of a narrow resonance are set as a function of the mass, and are interpreted as upper limits on the ALP production coupling constant, assuming 100% decay branching ratio into a photon pair. The inferred upper limit on the coupling constant is in the range 0.04–0.09 TeV−1 at 95% confidence level.
G. Aad, B. Abbott, K. Abeling, S.H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A.C. Abusleme Hoffman, B.S. Acharya,et al.
Elsevier BV
G. Aad, B. Abbott, D.C. Abbott, A. Abed Abud, K. Abeling, S.H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Elsevier BV
G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A. C. Abusleme Hoffman,et al.
Springer Science and Business Media LLC
AbstractThe flavour-tagging algorithms developed by the ATLAS Collaboration and used to analyse its dataset of $$\\sqrt{s} = 13$$ s = 13 TeV pp collisions from Run 2 of the Large Hadron Collider are presented. These new tagging algorithms are based on recurrent and deep neural networks, and their performance is evaluated in simulated collision events. These developments yield considerable improvements over previous jet-flavour identification strategies. At the 77% b-jet identification efficiency operating point, light-jet (charm-jet) rejection factors of 170 (5) are achieved in a sample of simulated Standard Model $$t\\bar{t}$$ t t ¯ events; similarly, at a c-jet identification efficiency of 30%, a light-jet (b-jet) rejection factor of 70 (9) is obtained.
, G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract A search for a new heavy scalar or pseudo-scalar Higgs boson (H/A) produced in association with a pair of top quarks, with the Higgs boson decaying into a pair of top quarks (H/A → $$ t\\overline{t} $$ t t ¯ ) is reported. The search targets a final state with exactly two leptons with same-sign electric charges or at least three leptons. The analysed dataset corresponds to an integrated luminosity of 139 fb−1 of proton–proton collisions collected at a centre-of-mass energy of 13 TeV with the ATLAS detector at the LHC. Two multivariate classifiers are used to separate the signal from the background. No significant excess of events over the Standard Model expectation is observed. The results are interpreted in the context of a type-II two-Higgs-doublet model. The observed (expected) upper limits at 95% confidence level on the $$ t\\overline{t}H/A $$ t t ¯ H / A production cross-section times the branching ratio of H/A → $$ t\\overline{t} $$ t t ¯ range between 14 (10) fb and 6 (5) fb for a heavy Higgs boson with mass between 400 GeV and 1000 GeV, respectively. Assuming that only one particle, either the scalar H or the pseudo-scalar A, contributes to the $$ t\\overline{t}t\\overline{t} $$ t t ¯ t t ¯ final state, values of tan β below 1.2 or 0.5 are excluded for a mass of 400 GeV or 1000 GeV, respectively. These exclusion ranges increase to tan β below 1.6 or 0.6 when both particles are considered.
, G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract A search for pair-produced scalar and vector leptoquarks decaying into quarks and leptons of different generations is presented. It uses the full LHC Run 2 (2015–2018) data set of 139 fb−1 collected with the ATLAS detector in proton–proton collisions at a centre-of-mass energy of $$ \\sqrt{s} $$ s = 13 TeV. Scalar leptoquarks with charge −(1/3)e as well as scalar and vector leptoquarks with charge +(2/3)e are considered. All possible decays of the pair-produced leptoquarks into quarks of the third generation (t, b) and charged or neutral leptons of the first or second generation (e, μ, ν) with exactly one electron or muon in the final state are investigated. No significant deviations from the Standard Model expectation are observed. Upper limits on the production cross-section are provided for eight models as a function of the leptoquark mass and the branching ratio of the leptoquark into the charged or neutral lepton. In addition, lower limits on the leptoquark masses are derived for all models across a range of branching ratios. Two of these models have the goal of providing an explanation for the recent B-anomalies. In both models, a vector leptoquark decays into charged and neutral leptons of the second generation with a similar branching fraction. Lower limits of 1980 GeV and 1710 GeV are set on the leptoquark mass for these two models.
G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti, A. C. Abusleme Hoffman,et al.
Springer Science and Business Media LLC
AbstractA search for a WZ resonance, in the fully leptonic final state (electrons or muons), is performed using 139 fb$$^{-1}$$ - 1 of data collected at a centre-of-mass energy of 13 TeV by the ATLAS detector at the Large Hadron Collider. The results are interpreted in terms of a singly charged Higgs boson of the Georgi–Machacek model, produced by WZ fusion, and of a Heavy Vector Triplet, with the resonance produced by WZ fusion or the Drell–Yan process. No significant excess over the Standard Model prediction is observed and limits are set on the production cross-section times branching ratio as a function of the resonance mass for these processes.
, G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract A search for resonances in events with at least one isolated lepton (e or μ) and two jets is performed using 139 fb−1 of $$ \\sqrt{s} $$ s = 13 TeV proton–proton collision data recorded by the ATLAS detector at the LHC. Deviations from a smoothly falling background hypothesis are tested in three- and four-body invariant mass distributions constructed from leptons and jets, including jets identified as originating from bottom quarks. Model-independent limits on generic resonances characterised by cascade decays of particles leading to multiple jets and leptons in the final state are presented. The limits are calculated using Gaussian shapes with different widths for the invariant masses. The multi-body invariant masses are also used to set 95% confidence level upper limits on the cross-section times branching ratios for the production and subsequent decay of resonances predicted by several new physics scenarios.
, G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract A search for long-lived particles decaying into hadrons is presented. The analysis uses 139 fb−1 of pp collision data collected at $$ \\sqrt{s} $$ s = 13 TeV by the ATLAS detector at the LHC using events that contain multiple energetic jets and a displaced vertex. The search employs dedicated reconstruction techniques that significantly increase the sensitivity to long-lived particles decaying in the ATLAS inner detector. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed event yields are compatible with those expected from background processes. The results are used to set limits at 95% confidence level on model-independent cross sections for processes beyond the Standard Model, and on scenarios with pair-production of supersymmetric particles with long-lived electroweakinos that decay via a small R-parity-violating coupling. The pair-production of electroweakinos with masses below 1.5 TeV is excluded for mean proper lifetimes in the range from 0.03 ns to 1 ns. When produced in the decay of $$ m\\left(\\overset{\\sim }{g}\\right) $$ m g ~ = 2.4 TeV gluinos, electroweakinos with $$ m\\left({\\overset{\\sim }{\\chi}}_1^0\\right) $$ m χ ~ 1 0 = 1.5 TeV are excluded with lifetimes in the range of 0.02 ns to 4 ns.
, G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract A search for vector-like leptons in multilepton (two, three, or four-or-more electrons plus muons) final states with zero or more hadronic τ-lepton decays is presented. The search is performed using a dataset corresponding to an integrated luminosity of 139 fb−1 of proton-proton collisions at a centre-of-mass energy of 13 TeV recorded by the ATLAS detector at the LHC. To maximize the separation of signal and background, a machine-learning classifier is used. No excess of events is observed beyond the Standard Model expectation. Using a doublet vector-like lepton model, vector-like leptons coupling to third-generation Standard Model leptons are excluded in the mass range from 130 GeV to 900 GeV at the 95% confidence level, while the highest excluded mass is expected to be 970 GeV.
, G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract This paper presents direct searches for lepton flavour violation in Higgs boson decays, H → eτ and H → μτ, performed using data collected with the ATLAS detector at the LHC. The searches are based on a data sample of proton-proton collisions at a centre-of-mass energy $$ \\sqrt{s} $$ s = 13 TeV, corresponding to an integrated luminosity of 138 fb−1. Leptonic (τ → ℓνℓντ) and hadronic (τ → hadrons ντ) decays of the τ-lepton are considered. Two background estimation techniques are employed: the MC-template method, based on data-corrected simulation samples, and the Symmetry method, based on exploiting the symmetry between electrons and muons in the Standard Model backgrounds. No significant excess of events is observed and the results are interpreted as upper limits on lepton-flavour-violating branching ratios of the Higgs boson. The observed (expected) upper limits set on the branching ratios at 95% confidence level, $$ \\mathcal{B} $$ B (H → eτ) < 0.20% (0.12%) and $$ \\mathcal{B} $$ B (H → μτ ) < 0.18% (0.09%), are obtained with the MC-template method from a simultaneous measurement of potential H → eτ and H → μτ signals. The best-fit branching ratio difference, $$ \\mathcal{B} $$ B (H → μτ) → $$ \\mathcal{B} $$ B (H → eτ), measured with the Symmetry method in the channel where the τ-lepton decays to leptons, is (0.25 ± 0.10)%, compatible with a value of zero within 2.5σ.
, G. Aad, B. Abbott, D. C. Abbott, K. Abeling, S. H. Abidi, A. Aboulhorma, H. Abramowicz, H. Abreu, Y. Abulaiti,et al.
Springer Science and Business Media LLC
Abstract This paper describes a search for dark photons (γd) in proton-proton collisions at $$ \\sqrt{s} $$ s = 13 TeV at the Large Hadron Collider (LHC). The dark photons are searched for in the decay of Higgs bosons (H → γγd) produced through the ZH production mode. The transverse mass of the system, made of the photon and the missing transverse momentum from the non-interacting γd, presents a distinctive signature as it peaks near the Higgs boson mass. The results presented use the total Run-2 integrated luminosity of 139 fb−1 recorded by the ATLAS detector at the LHC. The dominant reducible background processes are estimated using data-driven techniques. A Boosted Decision Tree technique is adopted to enhance the sensitivity of the search. As no excess is observed with respect to the Standard Model prediction, an observed (expected) upper limit on the branching ratio BR(H → γγd) of 2.28% ($$ {2.82}_{-0.84}^{+1.33}\\% $$ 2.82 − 0.84 + 1.33 % ) is set at 95% CL for massless γd. For massive dark photons up to 40 GeV, the observed (expected) upper limits on BR(H → γγd) at 95% confidence level is found within the [2.19,2.52]% ([2.71,3.11]%) range.