Probing the nature of electroweak symmetry breaking with Higgs boson pairs in ATLAS

Constraints on the Higgs boson trilinear self-coupling modifier $\kappa_{\lambda}$ and non-SM HHVV coupling strength $\kappa_{2V}$ are set by combining di-Higgs boson analyses using $b\bar{b}b\bar{b}$, $b\bar{b}\tau^{+}\tau^{-}$ and $b\bar{b}\gamma\gamma$ decay channels. The data used in these analyses were recorded by the ATLAS detector at the Large Hadron Collider in proton-proton collisions at $\sqrt{s}$ = 13 TeV and corresponding to an integrated luminosity of 126-139 $fb^{-1}$. The combination of the di-Higgs analyses sets an upper limit of signal strength $\mu_{HH} <$ 2.4 at 95\% confidence level on the di-Higgs production and constraints for $\kappa_{\lambda}$ between -0.6 and 6.6. The obtained confidence interval for $\kappa_{2V}$ coupling modifier are [0.1,2.0]. The High Luminosity Large Hadron Collider prospects have been considered as well. The expected signal strength is 0.55 and $\kappa_{\lambda}$ between 0.0 and 2.5 for the baseline scenario.Comment: DIS202

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements