Rubin-LSST

Abstract:

Constraints on the Higgs boson self-coupling are set by combining double-Higgs boson analyses in the bb̅bb̅, bb̅τ⁺τ⁻ and bb̅γγ decay channels with single-Higgs boson analyses targeting the γγ, ZZ^∗, WW^∗, τ⁺τ⁻ and bb̅ decay channels. The data used in these analyses were recorded by the ATLAS detector at the LHC in proton–proton collisions at √s = 13 TeV and correspond to an integrated luminosity of 126–139 fb⁻¹. The combination of the double-Higgs analyses sets an upper limit of μ_HH <2.4 at 95% confidence level on the double-Higgs production cross-section normalised to its Standard Model prediction. Combining the single-Higgs and double-Higgs analyses, with the assumption that new physics affects only the Higgs boson self-coupling (λ_HHH ), values outside the interval −0.4 < κ_λ = (λ_HHH /λ^SM_HHH) < 6.3 are excluded at 95% confidence level. The combined single-Higgs and double-Higgs analyses provide results with fewer assumptions, by adding in the fit more coupling modifiers introduced to account for the Higgs boson interactions with the other Standard Model particles. In this relaxed scenario, the constraint becomes −1.4 < κ_λ < 6.1 at 95% CL.

Abstract:

In this letter we present results for next-to-leading-order electroweak corrections to doubly polarised W$^+$W$^-$ production at the LHC in the fully leptonic decay channel. We model the production and the decay of two polarised W bosons in the double-pole approximation, including factorisable real and virtual electroweak corrections, and separating polarisation states at amplitude level. We obtain integrated and differential predictions for polarised signals in a realistic fiducial setup.Comment: 10 pages, 1 table, 4 figure

Abstract:

A measurement of the polarisation of W bosons produced in top-quark decays is presented, using proton–proton collision data at a centre-of-mass energy of √s = 13 TeV. The data were collected by the ATLAS detector at the Large Hadron Collider and correspond to an integrated luminosity of 139 fb−1. The measurement is performed selecting tt¯ events decaying into final states with two charged leptons (electrons or muons) and at least two b-tagged jets. The polarisation is extracted from the differential cross-section distribution of the cos θ ∗ variable, where θ ∗ is the angle between the momentum direction of the charged lepton from the W boson decay and the reversed momentum direction of the b-quark from the top-quark decay, both calculated in the W boson rest frame. Parton-level results, corrected for the detector acceptance and resolution, are presented for the cos θ ∗ angle. The measured fractions of longitudinal, left- and right-handed polarisation states are found to be f0 = 0.684 ± 0.005 (stat.) ± 0.014 (syst.), fL = 0.318 ± 0.003 (stat.) ± 0.008 (syst.) and fR = −0.002 ± 0.002 (stat.) ± 0.014 (syst.), in agreement with the Standard Model prediction