Photoproduction of pion pairs at high energy and small angles

TL;DR

This paper investigates the mechanisms of pion pair photoproduction near threshold energies, analyzing Coulomb, sigma meson, and charge exchange processes to understand their contributions to cross sections.

Contribution

It provides a comprehensive quantitative analysis of multiple pion production mechanisms, including electromagnetic and strong interactions, in a unified framework.

Findings

Charged pion pairs are produced via Coulomb and omega exchange mechanisms.

Sigma meson production and decay into pions significantly contribute near threshold.

Two-step charge exchange process is important for neutral pion production.

Abstract

We explore the photoproduction mechanisms for charged and neutral pion pairs off a heavy nucleus at threshold. We calculate the production of charged pairs in the Coulomb field of the nucleus in the Born approximation using explicit expressions for the differential cross sections and their connection with the total cross-section. The production of sigma mesons at threshold and their subsequent decay into pions is an important mechanism and is investigated quantitatively in a framework that can be used for both charged and neutral pions. Sigma mesons can be produced via electromagnetic (photon exchange) or strong (omega exchange) interactions. For neutral pions, another important production mechanism consists of the two-step process where charged pions are produced first and then charge exchange into two neutral pions. Differential and total cross sections are computed for each production mechanism.