Abstract
Abstract:
A search for weakly interacting massive dark-matter particles produced in association with
bottom or top quarks is presented. Final states containing third-generation quarks and missing
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 interpreted 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.