Evidence for the associated production of the Higgs boson and a top quark pair with the ATLAS detector

Abstract

A search for the associated production of the Higgs boson with a top quark pair (ttH) is reported. The search is performed in multilepton final states using a data set corresponding to an integrated luminosity of 36.1 fb −1 of proton-proton collision data recorded by the ATLAS experiment at a center-of-mass energy ffiffi ffi s p ¼ 13 −50 fb. The combination of this result with other ttH searches from the ATLAS experiment using the Higgs boson decay modes to bb, γγ and ZZ Ã → 4l, has an observed significance of 4.2 standard deviations, compared to an expectation of 3.8 standard deviations. This provides evidence for the ttH production mode.

Higgs couplings at high scales

“…The ATLAS and CMS collaborations have so far established a consistent picture of the Higgs boson couplings at the EW scale Q 2 ≈ m 2 h to top quarks directly [13,14] and indirectly [15,16], and to W þ W − [17,18], ZZ [15,16], ττ [19,20], and bb directly [21,22]. Experiments at the LHC will continue to probe the Higgs sector both at the Higgs mass scale as well as at higher scales.…”

Nonminimal dark sectors: Mediator-induced decay chains and multijet collider signatures

“…Similarly, the dashed black jagged line separates the points within out parameter-space scan which satisfy the bound from the moderate-jet-multiplicity search limits derived in Ref. [58] from the points which do not. The regions above and to the right of each contour are excluded by the corresponding constraint.…”

“…10 indicates that a significant number of events with 5-6 jets can be produced even within regions of parameter space where the peak on the N jet distribution is much higher. The leading constraints of this sort turn out to be those from an ATLAS search [58] for squarks and gluinos in events involving 2-6 hadronic jets and substantial / E T . However, as we shall see, constraints from such moderate-jet-multiplicity searches turn out to be subleading compared to those from the monojet + / E T and multi-jet + / E T searches discussed above.…”

Lepton number violation in heavy Higgs boson decays to sneutrinos

“…Although the final state contains neutrinos, it will be possible to get an estimate of m H , which results in an upper bound for the sneutrino mass of mÑ ≤ m H /2. The chargino mass has already some lower limits from direct searches [40,41] and, if the higgsinos are light, we would expect a signal to emerge from searches for SUSY with compressed spectra.…”

“…We have prepared a set of Benchmark Points (BPs). The experimental lower bound for the lightest higgsino is around 160 GeV as the mass differences between the other higgsinos are in the range of 5-10 GeV [40,41]. We take the higgsino masses close to this lower bound and choose the soft SUSY breaking sneutrino masses so that the sneutrinos are between 200…”