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ATLAS Collaboration(Aad, G. et al), Aikot, A., Amos, K. R., Bouchhar, N., Cabrera Urban, S., Cantero, J., et al. (2025). Differential cross-section measurements of Higgs boson production in the H → τ+τ- decay channel in pp collisions at √s=13 TeV with the ATLAS detector. J. High Energy Phys., 03(3), 010–66pp.
Abstract: Differential measurements of Higgs boson production in the tau-lepton-pair decay channel are presented in the gluon fusion, vector-boson fusion (VBF), VH and t (t) over barH associated production modes, with particular focus on the VBF production mode. The data used to perform the measurements correspond to 140 fb(-1) of proton-proton collisions collected by the ATLAS experiment at the LHC. Two methods are used to perform the measurements: the Simplified Template Cross-Section (STXS) approach and an Unfolded Fiducial Differential measurement considering only the VBF phase space. For the STXS measurement, events are categorized by their production mode and kinematic properties such as the Higgs boson's transverse momentum (p(T)(H)), the number of jets produced in association with the Higgs boson, or the invariant mass of the two leading jets (m(jj)). For the VBF production mode, the ratio of the measured cross-section to the Standard Model prediction for m(jj) > 1.5 TeV and p(T)(H) > 200 GeV (p(T)(H) < 200 GeV) is 1.29(-0.34)(+0.39) (0.12(-0.33)(+0.34)). This is the first VBF measurement for the higher-p(T)(H) criteria, and the most precise for the lower-p(T)(H) criteria. The fiducial cross-section measurements, which only consider the kinematic properties of the event, are performed as functions of variables characterizing the VBF topology, such as the signed Delta phi(jj) between the two leading jets. The measurements have a precision of 30%-50% and agree well with the Standard Model predictions. These results are interpreted in the SMEFT framework, and place the strongest constraints to date on the CP-odd Wilson coefficient c(H (W) over tilde).
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ATLAS Collaboration(Aad, G. et al), Cabrera Urban, S., Castillo Gimenez, V., Costa, M. J., Fassi, F., Ferrer, A., et al. (2013). Measurement of the distributions of event-by-event flow harmonics in lead-lead collisions at root s(NN)=2.76 TeV with the ATLAS detector at the LHC. J. High Energy Phys., 11(11), 183–57pp.
Abstract: The distributions of event-by-event harmonic flow coefficients v (n) for n = 2- 4 are measured in = 2.76 TeV Pb + Pb collisions using the ATLAS detector at the LHC. The measurements are performed using charged particles with transverse momentum p (T) > 0.5 GeV and in the pseudorapidity range |eta| < 2.5 in a dataset of approximately 7 μb(-1) recorded in 2010. The shapes of the v (n) distributions suggest that the associated flow vectors are described by a two-dimensional Gaussian function in central collisions for v (2) and over most of the measured centrality range for v (3) and v (4). Significant deviations from this function are observed for v (2) in mid-central and peripheral collisions, and a small deviation is observed for v (3) in mid-central collisions. In order to be sensitive to these deviations, it is shown that the commonly used multi-particle cumulants, involving four particles or more, need to be measured with a precision better than a few percent. The v (n) distributions are also measured independently for charged particles with 0.5 < p (T) < 1 GeV and p (T) > 1 GeV. When these distributions are rescaled to the same mean values, the adjusted shapes are found to be nearly the same for these two p (T) ranges. The v (n) distributions are compared with the eccentricity distributions from two models for the initial collision geometry: a Glauber model and a model that includes corrections to the initial geometry due to gluon saturation effects. Both models fail to describe the experimental data consistently over most of the measured centrality range.
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