TAPIA, SEBASTIAN

The observation of the electroweak production of single-top-quarks is made using 255 pb−1 of proton-proton collision data recorded at s√=5.02 TeV with the ATLAS detector at the Large Hadron Collider. An event selection is used to identify single-top-quark candidates arising from t-channel production with the top quark decaying semi-leptonically. Events passing the selection are then used to measure the inclusive cross-section for the combined production of single-top-quarks and antiquarks, σ(tq+t¯q), and the ratio Rt between these two. They are measured to be σ(tq+t¯q)=27.1+4.4−4.1(stat.)+4.4−3.7(syst.) pb and Rt=2.73+1.43−0.82(stat.)+1.01−0.29(syst.). The individual single-top-quark (tq) and single-top-antiquark (t¯q) production cross-sections are measured to be σ(tq)=19.8+3.9−3.1(stat.)+2.9−2.2(syst.) pb and σ(t¯q)=7.3+3.2−2.1(stat.)+2.8−1.5(syst.) pb. All measurements are in good agreement with the Standard Model predictions.

A search for the exclusive decays of the Higgs and Z bosons to a ϕ or ρ meson and a photon is performed with a pp collision data sample corresponding to an integrated luminosity of up to 35.6 fb−1 collected at s√=13 TeV with the ATLAS detector at the CERN Large Hadron Collider. These decays have been suggested as a probe of the Higgs boson couplings to light quarks. No significant excess of events is observed above the background, as expected from the Standard Model. Upper limits at 95% confidence level were obtained on the branching fractions of the Higgs boson decays to ϕγ and ργ of 5.0×10−4 and 10.4×10−4, respectively. The corresponding 95% confidence level upper limits for the Z boson decays are 0.7×10−6 and 4.0×10−6 for ϕγ and ργ, respectively.

Fiducial and total 𝑊 ± and 𝑍 boson cross sections, their ratios and the ratio of top-antitop-quark pair and 𝑊 -boson fiducial cross sections are measured in proton–proton collisions at a centre-of-mass energy of √𝑠 = 13.6 TeV, corresponding to an integrated luminosity of 29 fb−1 of data collected in 2022 by the ATLAS experiment at the Large Hadron Collider. The measured fiducial cross-section values for 𝑊 + → 𝓁+𝜈, 𝑊 − → 𝓁−𝜈̄, and 𝑍 → 𝓁+𝓁− (𝓁 = 𝑒 or 𝜇) boson productions are 4250 ± 150 pb, 3310 ± 120 pb, and 744 ± 20 pb, respectively, where the uncertainty is the total uncertainty, including that arising from the luminosity of about 2.2%. The measurements are in agreement with Standard-Model predictions calculated at next-to-next-to-leading-order in 𝛼𝑠 , next-to-nextto-leading logarithmic accuracy and next-to-leading-order electroweak accuracy

ATLAS measured the centrality dependence of the dijet yield using 165  nb−1 of 𝑝+Pb data collected at √𝑠NN=8.16  TeV in 2016. The event centrality, which reflects the 𝑝+Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, 𝑅CP, is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The 𝑅CP shows a scaling with the Bjorken 𝑥 of the parton originating from the proton, 𝑥𝑝, while no such trend is observed as a function of 𝑥Pb. This analysis provides unique input to understanding the role of small proton spatial configurations in 𝑝+Pb collisions by covering parton momentum fractions from the valence region down to 𝑥𝑝∼10−3 and 𝑥Pb∼4×10−4.