Analysis of weak-interaction effects in high-transverse-momentum hadron-hadron collisions

Abstract

Parity-violating (pv) weak effects in inclusive hadron-hadron scattering processes such as $\mathrm{pp}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}X$ and $\mathrm{pp}\ensuremath{\rightarrow}\ensuremath{\Lambda}X$ are studied in the framework of the parton model. Such effects arise from the coherent interference of the strong and weak parton-parton scattering amplitudes, and manifest themselves experimentally through a difference in the cross sections for protons incident with initial \ifmmode\pm\else\textpm\fi{} helicity, or through a longitudinal polarization of the outgoing $\ensuremath{\Lambda}$ produced by an unpolarized beam. Results for the corresponding pv parameters $\mathcal{a}$ and $\mathcal{p}$ are presented assuming a variety of weak-interaction models. For the strong parton-parton interaction we use the recently introduced effective-gluon model. A detailed discussion is given of phases in the weak and strong interactions and of the strong-weak relative phase in various models. It is shown that both $|\mathcal{a}|$ and $|\mathcal{p}|$ increase with increasing $\sqrt{s}$ and ${x}_{\ensuremath{\perp}}=\frac{2{p}_{\ensuremath{\perp}}}{\sqrt{s}}$, where $\sqrt{s}$ is the center-of-momentum energy and ${p}_{\ensuremath{\perp}}$ is the transverse momentum of the inclusively produced ${\ensuremath{\pi}}^{+}$ or $\ensuremath{\Lambda}$. For $\sqrt{s}=20$ GeV and ${x}_{\ensuremath{\perp}}=0.6$, $|\mathcal{a}|$ and $|\mathcal{p}|$ can be as large as ${10}^{\ensuremath{-}3}$-${10}^{\ensuremath{-}4}$ in some models, which may make such effects detectable in future experiments. In other models $\mathcal{a}$ and $\mathcal{p}$ can actually vanish identically for certain values of $\sqrt{s}$ and ${x}_{\ensuremath{\perp}}$ due to cancellation among the individual quark contributions. It is noted that, for a given weak-interaction model, the dependence of $\mathcal{a}$ and $\mathcal{p}$ on ${x}_{\ensuremath{\perp}}$ and $\sqrt{s}$ is different in the effective-gluon and constituent-interchange models, and hence weak effects can be used to discriminate among models of the strong interaction. A discussion is also given of various experimental problems associated with measuring $\mathcal{a}$ and $\mathcal{p}$.