Search for single production of a vectorlike T quark decaying into a Higgs boson and top quark with fully hadronic final states using the ATLAS detector

Abstract

The ATLAS Collaboration A search is made for a vector-like 𝑇 quark decaying into a Higgs boson and a top quark in 13 TeV proton-proton collisions using the ATLAS detector at the Large Hadron Collider with a data sample corresponding to an integrated luminosity of 139 fb −1. The Higgs-boson and top-quark candidates are identified in the all-hadronic decay mode, where 𝐻 → 𝑏 b and 𝑡 → 𝑏𝑊 → 𝑏𝑞 q are reconstructed as large-radius jets. The candidate Higgs boson, top quark, and associated B-hadrons are identified using tagging algorithms. No significant excess is observed above the background, so limits are set on the production cross-section of a singlet 𝑇 quark at 95% confidence level, depending on the mass, 𝑚 𝑇 , and coupling, 𝜅 𝑇 , of the vector-like 𝑇 quark to Standard Model particles. In the considered mass range between 1.0 and 2.3 TeV, the upper limit on the allowed coupling values increases with 𝑚 𝑇 from a minimum value of 0.35 for 1.07 < 𝑚 𝑇 < 1.4 TeV to 1.6 for 𝑚 𝑇 = 2.3 TeV.

Form factors in Higgs couplings from physics beyond the standard model

“…As a first example, we consider composite Higgs models (CHMs) [21][22][23] to demonstrate the main features of momentum dependence in the Higgs couplings, since they allow us to construct the Higgs form factors explicitly. Additionally, they are well motivated BSM candidates, providing a solution to the hierarchy problem and are consistent with the current JHEP10(2022)004 experimental bounds from the LHC [24,25]. While interesting models on their own, most of this section can be viewed as an application of the general ideas discussed in section 2.…”

Heavy vector-like quarks decaying to exotic scalars: a case study with triplets

“…Pair production of VLQs at hadron collider is mainly governed by QCD interactions, leading to a cross-section which only depends on the mass of the VLQs and the centre-of-mass energy of the collider. Extensive searches for VLQs have been conducted at the LHC by both ATLAS and CMS collaborations, resulting in stringent bounds on the VLQ mass surpassing the TeV scale, irrespective of their specific decays into SM particles [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54]. However, two aspects have to be taken into account when interpreting current bounds:…”

Beyond the standard model searches in the top quark sectors at ATLAS and CMS

“…1 (left). The ATLAS Experiment has conducted a search for singly-produced VLQ decaying to a top quark and a Higgs boson in the hadronic final state [4] targetting the topology where both the top quark and the Higgs boson have large transverse momenta so that their decay products are merged into single large-radius jets. Deep neural network based algorithms are used to identify large-sized jet from hadronic top decay, and an n-subjettiness variable τ 21 [5], sensitive to 2-prong structure, is used to select the jet from H → b b decay.…”

“…[14]. Figure 1: The 95% CL observed lower mass limits on pair-produced (left) and singly produced (right) top-like quark masses [3,4].…”