Measurements of Higgs boson production by gluon-gluon fusion and vector-boson fusion using H→WW*→eνμν decays in pp collisions at s=13 TeV with the ATLAS detector

Higgs boson production via gluon-gluon fusion and vector-boson fusion in proton-proton collisions is measured in the H → W W ∗ → e ν μ ν 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 → W W ∗ branching ratio are measured to be 12.0 ± 1.4 and 0.75   + 0.19 − 0.16     pb , respectively, in agreement with the Standard Model predictions of 10.4 ± 0.6 and 0.81 ± 0.02     pb . Higgs boson production is further characterized through measurements of Simplified Template Cross Sections in a total of 11 kinematic fiducial regions

Anomaly detection search for new resonances decaying into a Higgs boson and a generic new particle X in hadronic final states using s=13 TeV pp collisions with the ATLAS detector

A search is presented for a heavy resonance Y decaying into a Standard Model Higgs boson H and a new particle X in a fully hadronic final state. The full Large Hadron Collider run 2 dataset of proton-proton collisions at..

Search for flavor-changing neutral-current couplings between the top quark and the <math display="inline"><mi>Z</mi></math> boson with proton-proton collisions at <math display="inline"><msqrt><mi>s</mi></msqrt><mo>=</mo><mn>13</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math> with the ATLAS detector

International audienceA search for flavor-changing neutral-current couplings between a top quark, an up or charm quark, and a Z boson is presented, using proton–proton collision data at s=13  TeV collected by the ATLAS detector at the Large Hadron Collider. The analyzed data set corresponds to an integrated luminosity of 139  fb-1. The search targets both single-top-quark events produced as gq→tZ (with q=u, c) and top-quark-pair events, with one top quark decaying through the t→Zq channel. The analysis considers events with three leptons (electrons or muons), a b-tagged jet, possible additional jets, and missing transverse momentum. The data are found to be consistent with the background-only hypothesis and 95% confidence-level limits on the t→Zq branching ratios, assuming only tensor operators of the Standard Model effective field theory framework contribute to the tZq vertices. These are 6.2×10-5 (13×10-5) for t→Zu (t→Zc) for a left-handed tZq coupling, and 6.6×10-5 (12×10-5) in the case of a right-handed coupling. These results are interpreted as 95% CL upper limits on the strength of the corresponding couplings, yielding limits for |CuW(13)*| and |CuB(13)*| (|CuW(31)| and |CuB(31)|) of 0.15 (0.16), and limits for |CuW(23)*| and |CuB(23)*| (|CuW(32)| and |CuB(32)|) of 0.22 (0.21), assuming a new-physics energy scale ΛNP of 1 TeV

Pursuit of paired dijet resonances in the Run 2 dataset with ATLAS

New particles with large masses that decay into hadronically interacting particles are predicted by many models of physics beyond the Standard Model. A search for a massive resonance that decays into pairs of dijet resonances is performed using..

Search for a new pseudoscalar decaying into a pair of muons in events with a top-quark pair at s=13 TeV with the ATLAS detector

A search for a new pseudoscalar Formula Presented-boson produced in events with a top-quark pair, where the Formula Presented-boson decays into a pair of muons, is performed using Formula Presented Formula Presented collision data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of Formula Presented. The search targets the final state where only one top quark decays to an electron or muon, resulting in a signature with three leptons Formula Presented and Formula Presented. No significant excess of events above the Standard Model expectation is observed and upper limits are set on two signal models: Formula Presented and Formula Presented with Formula Presented, Formula Presented, where Formula Presented, in the mass ranges Formula Presented and Formula Presented

Measurement of cross sections for production of a Z boson in association with a flavor-inclusive or doubly b-tagged large-radius jet in proton-proton collisions at s=13 TeV with the ATLAS experiment

We present measurements of cross sections for production of a leptonically decaying Z boson in association with a large-radius jet in 13 TeV proton-proton collisions at the LHC, using 36     fb − 1 of data from the ATLAS detector. Integrated and differential cross sections are measured at particle level in both a flavor inclusive and a doubly b -tagged fiducial phase space. The large-radius jet mass and transverse momentum, its kinematic relationship to the Z boson, and the angular separation of b -tagged small-radius track jets within the large-radius jet are measured. This measurement constitutes an important test of perturbative quantum chromodynamics in kinematic and flavor configurations relevant to several Higgs boson and beyond-Standard-Model physics analyses. The results highlight issues with modeling of additional hadronic activity in the flavor-inclusive selection, and a distinction between flavor-number schemes in the b -tagged phase space

Longitudinal Flow Decorrelations in Xe+Xe Collisions at sNN=5.44 TeV with the ATLAS Detector

The first measurement of longitudinal decorrelations of harmonic flow amplitudes v n for n = 2 – 4 in Xe + Xe collisions at √ s N N = 5.44     TeV is obtained using 3     μ b − 1 of data with the ATLAS detector at the LHC. The decorrelation signal for v 3 and v 4 is found to be nearly independent of collision centrality and transverse momentum ( p T ) requirements on final-state particles, but for v 2 a strong centrality and p T dependence is seen. When compared with the results from Pb + Pb collisions at √ s N N = 5.02     TeV , the longitudinal decorrelation signal in midcentral Xe + Xe collisions is found to be larger for v 2 , but smaller for v 3 . Current hydrodynamic models reproduce the ratios of the v n measured in Xe + Xe collisions to those in Pb + Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe + Xe and Pb + Pb . The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collision