Parity Nonconservation in Strong Interactions

TL;DR

This paper investigates parity nonconservation in strong interactions, focusing on top-quark polarization as a probe for new physics beyond QCD, exemplified by an s-channel massive X-gluon exchange.

Contribution

It introduces the concept of using top-quark polarization as a signal for parity nonconserving new physics in strong interactions, specifically through a model involving an X-gluon.

Findings

Longitudinal top-quark polarization vanishes in QCD.

Parity-violating new physics can produce measurable polarization.

X-gluon exchange can lead to significant polarization signals.

Abstract

For top-quarks produced via the subprocess $q\bar q\to t\bar t$, the longitudinal t-quark polarization ($P_{\parallel}$) vanishes in QCD. $P_{\parallel}$ can be measured by the angular distribution of the lepton in $t$-quark semileptonic decay. New physics contributions that are parity nonconserving will be manifest by non-vanishing $P_{\parallel}$, which may be large. We illustrate this with the s-channel exchange of a massive $X$-gluon with chiral quark couplings.