Octet scalars shaping LHC distributions in 4-jet final states

We study properties of a hypothetical scalar particle, \Theta Θ , which is a color octet and an electroweak singlet. At hadron colliders, \Theta Θ 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 q q ‾ through dimension-5 operators, and at one loop into gluons. Thus, the main LHC signature of \Theta Θ is a pair of dijets of equal invariant mass. The CMS search in this channel shows a 3.6\sigma 3.6 σ excess over the QCD background for a dijet mass M_{jj} ≈ 0.95 M j j ≈ 0.95 TeV, which can be due to \Theta Θ : 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) p p → Θ Θ → ( q q ‾ ) ( q q ‾ ) yield a rate consistent with the excess. Furthermore, the shape of the d\sigma/d M_{jj} d σ / d M j j signal is in agreement with the CMS result. Given the data-driven background fit performed by CMS, we find that a complex scalar (whose production rate is twice as large) 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 t t ‾ pair plus a dijet resonance, as well as final states involving a Higgs, W W or Z Z boson plus jets.