This Letter reports the observation of WZ gamma production and a measurement of its cross section using 140.1 +/- 1.2 fb(-1) of proton-proton collision data recorded at a center-of-mass energy of 13 ...TeV by the bosons decaying leptonically, pp -> WZ gamma -> l'(perpendicular to)nu l(+) l(-)gamma (l(')(+) = e, mu), is measured in a fiducial phasespace region defined such that the leptons and the photon have high transverse momentum and the photon is isolated. The cross section is found to be 2.01 +/- 0.30(stat) +/- 0.16(syst) fb. The corresponding standard model predicted cross section calculated at next-to-leading order in perturbative quantum chromodynamics and at leading order in the electroweak coupling constant is 1.50 +/- 0.06 fb. The observed significance of the WZ gamma signal is 6.3 sigma, compared with an expected significance of 5.0 sigma.
The 𝐶𝑃 properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb −1 of proton–proton collision data recorded by the ATLAS experiment at the LHC at a ...centre-of-mass energy of √𝑠 = 13 TeV. The 𝐶𝑃 structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of 𝑏-quarks and produced in association with either a pair of top quarks, 𝑡̄𝑡𝐻,or a single top quark, 𝑡𝐻. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in 𝑡̄𝑡𝐻 and 𝑡𝐻 events, where dedicated 𝐶𝑃 -sensitive observables are exploited. In an extension of the Standard Model (SM) with a 𝐶𝑃 -odd admixture in the top–Higgs Yukawa coupling, the mixing angle between 𝐶𝑃 -even and 𝐶𝑃 -odd couplings is measured to be 𝛼 = 11 ◦+52 ◦−73◦ , compatible with the SM prediction corresponding to 𝛼 = 0.
The inclusive top-quark-pair production cross section rrtt and its ratio to the Z-boson production cross section have been measured in proton-proton collisions at root s = 13.6 TeV, using 29 fb-1 of ...data collected in 2022 with the ATLAS experiment at the Large Hadron Collider. Using events with an opposite-charge electron-muon pair and b-tagged jets, and assuming Standard Model decays, the top-quark-pair production cross section is measured to be rrtt = 850 +/- 3(stat.) +/- 18(syst.) +/- 20(lumi.) pb. The ratio of the ttand the Z-boson production cross sections is also measured, where the Z-boson contribution is determined for inclusive e+e- and mu+mu- events in a fiducial phase space. The relative uncertainty on the ratio is reduced compared to the ttcross section, thanks to the cancellation of several systematic uncertainties. The result for the ratio, Rtt/Z = 1.145 +/- 0.003(stat.) +/- 0.021(syst.) +/- 0.002(lumi.) is consistent with the Standard Model prediction using the PDF4LHC21 PDF set.
The inclusive Higgs boson production crosssection is measured in the di-photon and the Z Z∗ → 4decay channels using 31.4 and 29.0 fb−1 of pp collision datarespectively, collected with the ATLAS ...detector at a centreof-mass energy of √s = 13.6 TeV. To reduce the modeldependence, the measurement in each channel is restrictedto a particle-level phase space that closely matches the channel’s detector-level kinematic selection, and it is correctedfor detector effects. These measured fiducial cross-sectionsare σfid,γ γ = 76+14−13 fb, and σfid,4 = 2.80 ± 0.74 fb, inagreement with the corresponding Standard Model predictions of 67.6±3.7 fb and 3.67±0.19 fb. Assuming StandardModel acceptances and branching fractions for the two channels, the fiducial measurements are extrapolated to the fullphase space yielding total cross-sections of σ (pp → H) =67+12−11 pb and 46±12 pb at 13.6 TeV from the di-photon andZ Z∗ → 4 measurements respectively. The two measurements are combined into a total cross-section measurement ofσ (pp → H) = 58.2±8.7 pb, to be compared with the Standard Model prediction of σ (pp → H)SM = 59.9 ± 2.6 pb.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A search for a long-lived, heavy neutral lepton (N) in 139 fb(-1) of vs = 13 TeV pp collision data collected by the ATLAS detector at the Large Hadron Collider is reported. The N is produced via W ?N ...mu 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.
Higgs boson production via gluon-gluon fusion and vector-boson fusion in proton-proton collisions is measured in the H & RARR; WW* & RARR; ev & mu;v decay channel. The Large Hadron ...Collider delivered proton-proton collisions at a center-of-mass energy of 13 TeV between 2015 and 2018, which were recorded by the ATLAS detector, corresponding to an integrated luminosity of 139 fb-1. The total cross sections for Higgs boson production by gluon-gluon fusion and vector-boson fusion times the H & RARR; WW* branching ratio are measured to be 12.0 1 1.4 and 0.75 thorn 0.19 -0.16 pb, respectively, in agreement with the Standard Model predictions of 10.4 1 0.6 and 0.81 1 0.02 pb. Higgs boson production is further characterized through measurements of Simplified Template Cross Sections in a total of 11 kinematic fiducial regions.
A search for the pair-production of vector-like quarks optimized for decays into a Z boson and a third-generation Standard Model quark is presented, using the full Run 2 dataset corresponding to 139 ...fb-1 of pp collisions at & RADIC;s = 13 TeV, collected in 2015-2018 with the ATLAS detector at the Large Hadron Collider. The targeted final state is characterized by the presence of a Z boson with high transverse momentum, reconstructed from a pair of same-flavour leptons with opposite-sign charges, as well as by the presence of b-tagged jets and high-transverse-momentum large-radius jets reconstructed from calibrated smaller-radius jets. Events with exactly two or at least three leptons are used, which are further categorized by the presence of boosted W, Z, and Higgs bosons and top quarks. The categorization is performed using a neural-network-based boosted object tagger to enhance the sensitivity to signal relative to the background. No significant excess above the background expectation is observed and exclusion limits at 95% confidence level are set on the masses of the vector-like partners T and B of the top and bottom quarks, respectively. The limits depend on the branching ratio configurations and, in the case of 100% branching ratio for T-+ Zt and 100% branching ratio for B-+ Zb, this search sets the most stringent limits to date, allowing mT > 1.60 TeV and mB > 1.42 TeV, respectively.
Results of a measurement of dimuon photoproduction in nonultraperipheral Pb + Pb collisions at root sNN = 5.02 TeV are presented. The measurement uses ATLAS data from the 2015 and 2018 Pb + Pb ...data-taking periods at the LHC with an integrated luminosity of 1.94 nb-1. The gamma gamma -> mu+mu- pairs are identified via selections on pair momentum asymmetry and acoplanarity. Differential cross sections for dimuon production are measured in different centrality, average muon momentum, and pair rapidity intervals as functions of acoplanarity and k perpendicular to, the transverse momentum kick of one muon relative to the other. Measurements are also made as a function of the rapidity separation of the muons and the angle of the muon pair relative to the second-order event plane to test whether magnetic fields generated in the quark-gluon plasma affect the measured muons. A prior observation of a centrality-dependent broadening of the acoplanarity distribution is confirmed. Furthermore, the improved precision of the measurement reveals a depletion in the number of pairs having small acoplanarity or k perpendicular to values in more central collisions. The acoplanarity distributions in a given centrality interval are observed to vary with the mean pT of the muons in the pair, but the k perpendicular to distributions do not. Comparisons with recent theoretical predictions are made. The predicted trends associated with effects of magnetic fields on the dimuons are not observed.
This paper presents a search for hypothetical massive, charged, long-lived particles with the ATLAS detector at the LHC using an integrated luminosity of 139 fb(-1) of proton-proton collisions at ...root s = 13 TeV. These particles are expected to move significantly slower than the speed of light and should be identifiable by their high transverse momenta and anomalously large specific ionisation losses, dE/dx. Trajectories reconstructed solely by the inner tracking system and a dE/dx measurement in the pixel detector layers provide sensitivity to particles with lifetimes down to O(1) ns with a mass, measured using the Bethe-Bloch relation, ranging from 100 GeV to 3 TeV. Interpretations for pair-production of R-hadrons, charginos and staus in scenarios of supersymmetry compatible with these particles being long-lived are presented, with mass limits extending considerably beyond those from previous searches in broad ranges of lifetime.
This paper presents a search for a new Z' vector gauge boson with the ATLAS experiment at the Large Hadron Collider using pp collision data collected at root s = 13TeV, corresponding to an integrated ...luminosity of 139 fb(-1). The new gauge boson Z' is predicted by L-mu - L-tau models to address observed phenomena that can not be explained by the Standard Model. The search examines the four-muon (4 mu) final state, using a deep learning neural network classifier to separate the Z' signal from the Standard Model background events. The di-muon invariant masses in the 4 mu events are used to extract the Z' resonance signature. No significant excess of events is observed over the predicted background. Upper limits at a 95% confidence level on the Z' production cross-section times the decay branching fraction of pp -> Z' mu mu -> 4 mu are set from 0.31 to 4.3 fb for the Z' mass ranging from 5 to 81 GeV. The corresponding common coupling strengths, g(Z'), of the Z' boson to the second and third generation leptons above 0.003 - 0.2 have been excluded.
