Single lepton charge asymmetries in t {bar{t}} and t {bar{t}} gamma production at the LHC

J A Aguilar-Saavedra

doi:10.1140/epjc/s10052-018-5917-7

J A Aguilar-Saavedra

Open Access

https://doi.org/10.1140/epjc/s10052-018-5917-7

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Abstract

We discuss lepton charge asymmetries in t {bar{t}} and t {bar{t}} gamma production at the LHC, which can be measured in the semileptonic decay channel t {bar{t}} rightarrow W^+ b , W^- {bar{b}} rightarrow ell ^+ nu b , q {bar{q}}' {bar{b}} (or the charge conjugate). Considering several variants of a new physics scenario with a light colour octet, it is seen that for t {bar{t}} these asymmetries may have a sensitivity competitive with the dilepton asymmetry already measured. For t {bar{t}} gamma the new leptonic asymmetries, as well as the t {bar{t}} charge asymmetry, will reach their full potential with the high luminosity LHC upgrade. These asymmetries can pinpoint deviations at the 3sigma -4sigma level for new physics scenarios where the charge asymmetries already measured in t {bar{t}} production agree within 1sigma .

Highlights

Charge asymmetries in ttproduction at hadron colliders [1] arouse wide interest after measurements by the CDF and D0 Collaborations of the forward-backward (FB) asymmetry AFB in ttproduction at the Tevatron [2,3] showed some deviations from the existing standard model (SM) predictions [4]
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
We examine the potential of the new single lepton asymmetries by using as new physics benchmark a light colour octet below the ttthreshold [40] with mass M = 250 GeV and large width = 0.2M

Summary

Introduction

Charge asymmetries in ttproduction at hadron colliders [1] arouse wide interest after measurements by the CDF and D0 Collaborations of the forward-backward (FB) asymmetry AFB in ttproduction at the Tevatron [2,3] showed some deviations from the existing standard model (SM) predictions [4]. These anomalies boosted the already extensive program to measure the top quark properties, and in particular they provided a strong motivation for the measurement of a charge asymmetry AC in ttproduction at the Large Hadron Collider (LHC). That might well be due to some mismodelling of ttproduction or, otherwise, some more contrived form of new physics, perhaps with different coupling to uuand ddsince – as it can be clearly seen from Fig. 2 – for simple new physics extensions the extra contributions to AFB and AC are quite correlated and have the same sign

TeV ll C

Predictions for t t

Discussion