Octet scalars shaping LHC distributions in 4-jet final states

Abstract

We study properties of a hypothetical scalar particle, $\Theta$, which is a color octet and an electroweak singlet. At hadron colliders, $\Theta$ is pair produced through its QCD coupling to gluons, so that its mass determines the cross section. It decays at tree level into $q\bar q$ through dimension-5 operators, and at one loop into gluons. Thus, the main LHC signature of $\Theta$ is a pair of dijets of equal invariant mass. The CMS search in this channel shows a $3.6\sigma$ excess over the QCD background for a dijet mass $M_{jj} \approx 0.95$ TeV, which can be due to $\Theta$: its production cross section (65 fb for a real scalar) and the acceptance of the CMS event selection applied to $p p \to \Theta \Theta \to \! (q \bar q)(q \bar q)$ yield a rate consistent with the excess. Furthermore, the shape of the $d\sigma/d M_{jj}$ signal is in agreement with the CMS result. Given the data-driven background fit performed by CMS, we find that a complex scalar fits better the data than a real scalar. Besides the pair of dijets, testable LHC signals include a trijet-dijet topology, a $t\bar t$ pair plus a dijet resonance, as well as final states involving a Higgs, $W$ or $Z$ boson plus jets.