Searches for ttH (Multilepton+Diphoton) Production in ATLAS

TL;DR

This paper reports on searches for the production of a Higgs boson with top quark pairs (ttH) using multilepton and diphoton signatures in ATLAS data, providing measurements that align with Standard Model predictions.

Contribution

First LHC Run-2 results for ttH production in multilepton and diphoton channels, improving understanding of Higgs-top interactions and testing SM consistency.

Findings

Measured signal strength in multilepton channel: μ=2.5^{+1.3}_{-1.1}

Measured signal strength in diphoton channel: μ=-0.3^{+1.2}_{-1.0}

Results are consistent with Standard Model expectations.

Abstract

After the discovery of a Higgs boson, the measurements of its properties are at the forefront of research. The determination of the associated production of a Higgs boson and a pair of top quarks is of particular importance as the ttH Yukawa coupling is large and thus an excellent probe for physics beyond the Standard Model (SM). For the complete LHC Run-1 dataset, the combined ATLAS and CMS signal strength (defined as the ratio of measured cross-section to the SM prediction) was $\mu=2.3^{+0.7}_{-0.6}$, which indicated a mild excess with respect to the SM expectation. The results of the ttH search with multilepton and diphoton signatures are presented for the first LHC Run-2 data (13 fb$^{-1}$ at 13 TeV) recorded by the ATLAS experiment: $\mu=2.5^{+1.3}_{-1.1}$ for the multilepton analyses and $\mu=-0.3^{+1.2}_{-1.0}$ for the diphoton analyses. Both measurements are in agreement with the SM expectation.