Very light axigluons and the top asymmetry

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.

Section: Jhep08(2014)172mentioning

confidence: 99%

Portrait of a colour octet

Aguilar-Saavedra

2014

“…[44] it was shown that the deviation from the SM prediction to the measured Tevatron top forward-backward asymmetry could also be due to light axigluons. This idea has been discussed in different scenarios for axigluons with masses in the range of 50 − 1000 GeV [45][46][47][48][49], and usually with a large axigluon decay width to prevent strong bounds from measurements of tt invariant mass spectra. Extensive studies of the phenomenology of light axigluons have been performed, including [50][51][52][53][54][55][56][57][58][59].…”

Section: Jhep09(2014)084mentioning

confidence: 99%

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

Alte

Berge

Spiesberger

2014

Abstract:We investigate the discovery potential of light color-octet bosons in the mass range of 100-400 GeV in exclusive top-pair plus jet production at the LHC, pp → tt + jet. We study the impact of such bosons on the incline, the energy and the rapidity asymmetries. We show that light axigluons with large couplings to quarks can be discovered at the LHC with a luminosity of a few fb −1 . Almost all of the considered axigluon parameter space can be probed using the already available 2011/2012 LHC data. In a small-coupling scenario, axigluons could be discovered using the charge asymmetry with 65 fb −1 at the LHC and a center of mass energy of 14 TeV. We furthermore show that tt + jet production could reveal the existence of scenarios where axigluons couple with a different strength to upand down-type quarks.

“…Although QCD and QED can do so, it is known that the majority of new physics models need some flavor structure for the positive asymmetry. The only known possible new physics model without flavor structure is light axigluons [56][57][58][59]. Thus, the possibility of flavorless model building is thought exciting.…”

Section: Rg-induction Of Top Asymmetriesmentioning

confidence: 99%

Renormalization group-induced phenomena of top pairs from four-quark effective operators

Jung

Yoon

et al. 2014

Abstract:We study the renormalization group(RG) evolution of four-quark operators that contribute to the top pair production. In particular, we focus on the cases in which certain observables are first induced from the one-loop RG while being absent at treelevel. From the operator mixing pattern, we classify all such RG-induced phenomena and underlying models that can induce them. We then calculate the full one-loop QCD RG evolution as the leading estimator of the effects and address the question of which RG-induced phenomena have largest and observable effects. The answer is related to the color structure of QCD. The studied topics include the RG-induction of top asymmetries, polarizations and polarization mixings as well as issues arising at this order. The RGinduction of top asymmetries is further compared with the generation of asymmetries from QCD and QED at one-loop order. We finally discuss the validity of using the RG as the proxy of one-loop effects on the top pair production. As an aside, we clarify the oftenstudied relations between top pair observables.