Shedding light on the $ t\overline{t} $ asymmetry: the photon handle

Abstract

We investigate a charge asymmetry in ttγ production at the LHC that provides complementary information to the measured asymmetries in tt production. We estimate the experimental uncertainty in its measurement at the LHC with 8 and 14 TeV. For new physics models that simultaneously reproduce the asymmetry excess in tt at the Tevatron and the SM-like asymmetry at the LHC, the measurement in ttγ at the LHC could exhibit significant deviations with respect to the SM prediction.

Portrait of a colour octet

“…We have seen that SM-like outcomes of these measurements would not be conclusive, as there are regions of the parameter space for which A FB and A ℓ FB (and also A ℓℓ FB ) can be significantly larger than in the SM, yet the remaining measurements can be consistent with the SM expectation. In this case, the solution to the Tevatron asymmetry puzzle may arrive from other kinds of measurements [45,70]. Yet, for the parameter space that gives a global 1σ agreement with data, we have seen that sizeable deviations are possible in top polarisation observables, both at the LHC and the Tevatron.…”

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

“…In the ttγ process the same definition for the charge asymmetry A C has been proposed [36]. However, in order to achieve a good sensitivity to new physics contributions in the production, one has to design a suitable fiducial region where top radiative decays, i.e.…”

“…The associated ttγ production will provide a measurement of a charge asymmetry (also denoted as A C , for simplicity) that is independent from the one in tt production [36], because a hard photon emitted from the initial state couples differently to up and down quarks. Therefore, the ratio between possible new physics contributions from uū and dd intial states is quite different in tt and ttγ .…”

“…Their measurement in ttγ does not entail any extra combinatorial ambiguity, as might be the case for tt W , and the only significant issue with respect to tt production is the need to suppress radiative top decays with an extra photon, which can be achieved by suitable kinematical cuts, as demonstrated in ref. [36]. Because the measurements of these asymmetries are limited from statistics, we provide results for the highluminosity Large Hadron Collider (HL-LHC) with 3 ab −1 , where the measurements will reach their full potential.…”

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

“…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]. In particular, in ref.…”