arXiv subjects

Atlas Collaboration

Publications and source records attributed to Atlas Collaboration.

3 recordsLinked to original sources

arXiv2025

Measurement of the Higgs boson production in association with top quarks in multilepton final states in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

A measurement of the associated production of a top-quark pair with the Higgs boson ($t\bar{t}H$) in multilepton final states is presented. The analysis is based on a data sample of proton-proton collisions at $\sqrt{s}=13$ TeV recorded with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 140 fb$^{-1}$. Six final states defined by the number and flavour of reconstructed charged leptons are combined in a simultaneous likelihood fit to extract the $t\bar{t}H$ signal and constrain the most relevant backgrounds. The measured $t\bar{t}H$ cross-section normalised to Standard Model (SM) prediction is $\sigma_{t\bar tH}/\sigma^{\text{SM}}=0.63^{+0.20}_{-0.19}$. This result corresponds to an observed (expected) significance of 3.3$\sigma$ (5.3$\sigma$). Additionally, two other fits are used to measure the $t\bar{t}H$ cross-section differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, and to extract the associated production cross-section of a single top-quark with the Higgs boson ($tH$) together with the $t\bar{t}H$ one. The $CP$ structure of the top quark-Higgs boson Yukawa coupling is probed through analysis of $t\bar{t}H$ and $tH$ events. The results are compatible with the SM hypothesis, and values of the mixing angle between $CP$-even and $CP$-odd top-Higgs Yukawa couplings of $| \alpha | > 62^\circ$ are excluded at 68\% confidence level.

hep-ex↗

arXiv2022

Search for dark photons from Higgs boson decays via $ZH$ production with a photon plus missing transverse momentum signature from $pp$ collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

This paper describes a search for dark photons ($\gamma_d$) in proton-proton collisions at $\sqrt{s}=13$ TeV at the Large Hadron Collider (LHC). The dark photons are searched for in the decay of Higgs bosons ($H \to \gamma\gamma_d$) produced through the $ZH$ production mode. The transverse mass of the system, made of the photon and the missing transverse momentum from the non-interacting $\gamma_d$, presents a distinctive signature as it peaks near the Higgs boson mass. The results presented use the total Run-2 integrated luminosity of 139 fb$^{-1}$ recorded by the ATLAS detector at the LHC. The dominant reducible background processes are estimated using data-driven techniques. A Boosted Decision Tree technique is adopted to enhance the sensitivity of the search. As no excess is observed with respect to the Standard Model prediction, an observed (expected) upper limit on the branching ratio BR$(H\to \gamma\gamma_d)$ of 2.28$\%$ (2.82$^{+1.33}_{-0.84}\%$) is set at 95$\%$ CL for massless $\gamma_d$. For massive dark photons up to 40 GeV, the observed (expected) upper limits on BR$(H\to \gamma\gamma_d)$ at 95\% confidence level is found within the [2.19,2.52]$\%$ ([2.71,3.11]$\%$) range.

hep-ex↗

arXiv2019

Search for chargino-neutralino production with mass splittings near the electroweak scale in three-lepton final states in $\sqrt{s}$ = 13 TeV $pp$ collisions with the ATLAS detector

A search for supersymmetry through the pair production of electroweakinos with mass splittings near the electroweak scale and decaying via on-shell $W$ and $Z$ bosons is presented for a three-lepton final state. The analyzed proton-proton collision data taken at a center-of-mass energy of $\sqrt{s}$ = 13 TeV were collected between 2015 and 2018 by the ATLAS experiment at the Large Hadron Collider, corresponding to an integrated luminosity of 139 fb$^{-1}$. A search, emulating the recursive jigsaw reconstruction technique with easily reproducible laboratory-frame variables, is performed. The two excesses observed in the 2015-2016 data recursive jigsaw analysis in the low-mass three-lepton phase space are reproduced. Results with the full dataset are in agreement with the Standard Model expectations. They are interpreted to set exclusion limits at 95% confidence level on simplified models of chargino-neutralino pair production for masses up to 345 GeV.

hep-ex↗