Differential cross section and analyzing power of the ${\vec p}p{\to}pp{\pi}^0$ reaction at a beam energy of 390 MeV

TL;DR

This study measures the differential cross section and analyzing power of the proton-proton to proton-proton pion-zero reaction at 390 MeV, revealing interference effects and suggesting a long-range pion-production mechanism.

Contribution

First measurement of differential cross section and analyzing power at this energy, analyzing angular and momentum dependence, and proposing a simple model for pion-production.

Findings

Interference of s- and p-waves affects analyzing power.

Momentum dependence explained by wave interference.

Indication of a significant long-range component in pion production.

Abstract

The differential cross section and analyzing power $A_y$ of the ${\vec p}p{\to}pp{\pi}^0$ reaction have been measured at RCNP in coplanar geometry at a beam energy of 390 MeV and the dependence on both the pion emission angle and the relative momentum of the final protons have been extracted. The angular variation of Ay for the large values of the relative momentum studied here shows that this is primarily an effect of the interference of pion s- and p-waves and this interference can also explain the momentum dependence. Within the framework of a very simple model, these results would suggest that the pion-production operator has a significant long-range component.