First measurement of the forward-backward charge asymmetry in top quark pair production

Abstract

We present the first measurement of the integrated forward-backward charge asymmetry in top-antitop quark pair (ttbar) production in proton-antiproton collisions in the lepton plus jets final state. Using a b-jet tagging algorithm and kinematic reconstruction assuming ttbar+X production and decay, a sample of 0.9fb-1 of data, collected by the D0 experiment at the Fermilab Tevatron Collider, is used to measure the asymmetry for different jet multiplicities. The result is also used to set upper limits on ttbar+X production via a Z' resonance.

Figures (4)

• Figure 1: Forward-backward $t\bar{t}$ charge asymmetry predicted by mc@nlo as a function of the fourth-highest particle jet $p_T$.
• Figure 2: The geometric dilution and its uncertainty band as a function of generated $\left|\Delta y\right|$ for standard model $t\bar{t}+X$ production and $\geqslant 4$ jets.
• Figure 3: Comparison of data for $\geqslant 4$ jets with the fitted model as a function of ${\cal {L}}$ for events reconstructed (a) as forward ($\Delta y_{\text{reco}}>0$) and (b) as backward ($\Delta y_{\text{reco}}<0$). The number of events from each source is listed with its statistical uncertainty.
• Figure 4: 95% C.L. limits on the fraction of $t\bar{t}$ produced via a $Z'$ resonance as a function of the $Z'$ mass, under assumptions detailed in the text. Limits expected in the absence of a $Z'$ resonance are shown by the dashed curve, with the shaded bands showing limits one and two standard deviations away. The observed limits are shown by the solid curve, and the excluded region is hatched.