Portrait of a colour octet

Abstract

New colour octets stand out among the new physics proposals to explain the anomalous forward-backward asymmetry measured in tt production by the CDF experiment at the Tevatron. We perform a fit to tt observables at the Tevatron and the LHC, including total cross sections, various asymmetries and the top polarisation and spin correlations, to find the most likely parameters of a light colour octet to be consistent with data. In particular, an octet coupling only to right-handed quarks gives a good fit to all measurements. The implications from the general fit are drawn in terms of predictions for top polarisation observables whose measurements are yet not very precise, and observables which simply have not been measured.

Single lepton charge asymmetries in $$t {\bar{t}}$$ t t ¯ and

“…The various constraints from tt observables on the parameter space of a light octet with this mass and width were analysed in full detail in ref. [43]. Here we only include the most relevant constraints, namely…”

Measurement of the charge asymmetry in dileptonic decays of top quark pairs in pp collisions at s = 7 $$ \sqrt{s}=7 $$ TeV using the ATLAS detector

“…The inclusive measurement of A C and A tt C is furthermore compared to two models of physics beyond the Standard Model (BSM) [9] that could be invoked to explain an anomalous forward-backward asymmetry at the Tevatron, such as reported by the CDF experiment [24]. Two models with a new colour octet particle exchanged in the s-channel are considered.…”

“…It is the only quark in the Standard Model (SM) that decays before hadronization occurs, and the only quark with Yukawa coupling to the Higgs boson close to unity. A precise study of top quark properties could shed light on possible physics models beyond the SM [3][4][5][6][7][8][9]. This analysis uses a data set corresponding to an integrated luminosity of 4.6 fb −1 of Large Hadron Collider (LHC) proton-proton (pp) collisions at a centre-of-mass energy of 7 TeV collected by the ATLAS detector.…”

Top quark charge asymmetry: searching for light axigluons in t t ¯ $$ t\overline{t} $$ + jet production at the LHC

“…In particular, in ref. [60] it could be demonstrated that a fit of top quark measurements at the Tevatron and the LHC performed within the SM is improved considerably if a light axigluon is included in the theory (compare also [61][62][63][64][65] for model constraints from other measurements).…”