Coherent Photoproduction of pi^+ from 3^He

TL;DR

This study measures the differential cross section for the coherent photoproduction of pi^+ from helium-3, revealing discrepancies with existing theories and indicating the need for model improvements.

Contribution

First measurement of differential cross sections for gamma + helium-3 to pi^+ + triton, highlighting gaps in current theoretical models.

Findings

Large cross sections observed at various angles

Theoretical models only match data at backward angles

Additional components needed in models to explain results

Abstract

We have measured the differential cross section for the $\gamma$$^3$He$\rightarrow \pi^+ t$ reaction. This reaction was studied using the CEBAF Large Acceptance Spectrometer (CLAS) at Jefferson Lab. Real photons produced with the Hall-B bremsstrahlung tagging system in the energy range from 0.50 to 1.55 GeV were incident on a cryogenic liquid $^3$He target. The differential cross sections for the $\gamma$$^3$He$\rightarrow \pi^+ t$ reaction were measured as a function of photon-beam energy and pion-scattering angle. Theoretical predictions to date cannot explain the large cross sections except at backward angles, showing that additional components must be added to the model.