A search for resonances decaying into a Higgs boson and a new particle X in the XH → qqbb final state with the ATLAS detector

Abstract

A search for heavy resonances decaying into a Higgs boson (H) and a new particle (X) is reported, utilizing 36.1fb−1of proton–proton collision data at √s=13TeVcollected during 2015 and 2016 with the ATLAS detector at the CERN Large Hadron Collider. The particle Xis assumed to decay to a pair of light quarks, and the fully hadronic final state XH→q¯q b¯ bis analysed. The search considers the regime of high XHresonance masses, where the Xand Hbosons are both highly Lorentz-boosted and are each reconstructed using a single jet with large radius parameter. A two-dimensional phase space of XHmass versus Xmass is scanned for evidence of a signal, over a range of XHresonance mass values between 1TeV and 4TeV, and for Xparticles with masses from 50GeV to 1000GeV. All search results are consistent with the expectations for the background due to Standard Model processes, and 95% CL upper limits are set, as a function of XHand Xmasses, on the production cross-section of the XH→q¯q b¯bresonance.