Search for Low-Mass Dijet Resonances Using Trigger-Level Jets with the ATLAS Detector in pp Collisions at s=13  TeV

Abstract

Searches for dijet resonances with sub-TeV masses using the ATLAS detector at the Large Hadron Collider can be statistically limited by the bandwidth available to inclusive single-jet triggers, whose data-collection rates at low transverse momentum are much lower than the rate from standard model multijet production. This Letter describes a new search for dijet resonances where this limitation is overcome by recording only the event information calculated by the jet trigger algorithms, thereby allowing much higher event rates with reduced storage needs. The search targets low-mass dijet resonances in the range 450-1800 GeV. The analyzed data set has an integrated luminosity of up to 29.3 fb^{-1} and was recorded at a center-of-mass energy of 13 TeV. No excesses are found; limits are set on Gaussian-shaped contributions to the dijet mass distribution from new particles and on a model of dark-matter particles with axial-vector couplings to quarks.

Accessible lepton-number-violating models and negligible neutrino masses

“…For example, the dijet channel qq → Σ (∆) → qq can be used to probe the contact interaction (y 2 /M 2 Σ (∆) )q c q c q c q c , which are a valid description of colored-scalar exchange in the limit where the scalar masses are beyond the reach of the collider. Recent dijet studies at ATLAS and CMS [5,65,66] translate into a lower bound on the mass of scalar diquarks [67] and, in our case, imply masses for Σ, ∆, and C µ that exceed around 5 TeV, for order one couplings. Σ and ∆ will also mediate, at the tree level, processes like gg → ΣΣ (∆∆) → 4q.…”

“…The corresponding bounds, however, are expected to be weaker than those of dijet searches as long as the couplings between the new bosons and the quarks are order one. Note that the few TeV upper bound does not trivially apply for smaller couplings and lower masses for Σ and ∆ and C µ , see, for example, [65,66]. Relatively-light bosons that couple to quarks relatively strongly are know to survive collider constraints, see for example, [68].…”

Quark-gluon tagging: Machine learning vs detector

“…We consider two benchmark point for the Z mass, namely m Z = 450 GeV and m Z = 750 GeV, combined with g Z = 0.1, and simulate the signal and the background with Sherpa2.2.1 [45] to leading order. The selection criteria for a standard LHC search are at least two jets with [68] p T,j 1 > 220(185) GeV p T,j 2 > 85 GeV |η j | < 2.8 ,…”

LHC constraints and potential on resonant monotop production

“…Due to the large QCD background and because of trigger requirements, dijet searches at the LHC typically target high invariant masses, so that dedicated efforts are needed to test the low mass regions that are more relevant for the monotop model under consideration. At Run 2, the most recent ATLAS search based on an integrated luminosity of 37 fb −1 has a minimum reach of 1.1 TeV [53], while a low-mass dedicated search [54] (29.3 fb −1 ) overcomes the trigger limitation by recording only jet trigger information and reaches invariant masses as low as 450 GeV. Similarly, for the CMS analyses of 36 fb −1 of 13 TeV data [55], the high mass region starts at 1.6 TeV, whereas a trigger-based low-mass search allows for reaching down to masses of 600 GeV.…”

“…In the upper left panel, we reinterpreted the low mass CMS search in the boosted regime [56], whilst on the upper right panel, we considered the CDF analysis [58]. In the lower left panel, we focused on the trigger-based ATLAS analysis [54], and combined it with the similar CMS search [55] in the lower right panel, recalling that the CMS analysis is insensitive to any mσ value smaller than 600 GeV.…”