Measurements of polarized photo-pion production on longitudinally polarized HD and Implications for Convergence of the GDH Integral

TL;DR

This paper presents new measurements of polarized pion production on polarized HD, providing detailed angular distributions that inform the convergence of the GDH sum rule and reveal discrepancies with previous data and predictions.

Contribution

It offers the first comprehensive angular distributions of spin-difference cross sections for polarized HD near the Delta(1232) resonance, impacting GDH sum rule evaluations.

Findings

Measured pion production on polarized HD with nearly complete angular coverage.

Found that pi0 data suggest faster convergence of the GDH integral than previously thought.

Results for deuterium are more precise and generally lower than earlier measurements and calculations.

Abstract

We report new measurements of inclusive pion production from frozen-spin HD for polarized photon beams covering the Delta(1232) resonance. These provide data simultaneously on both H and D with nearly complete angular distributions of the spin-difference cross sections entering the Gerasimov-Drell-Hearn (GDH) sum rule. Recent results from Mainz and Bonn exceed the GDH prediction for the proton by 22 microbarns, suggesting as yet unmeasured high-energy components. Our pi0 data reveal a different angular dependence than assumed in Mainz analyses and integrate to a value that is 18 microbarns lower, suggesting a more rapid convergence. Our results for deuterium are somewhat lower than published data, considerably more precise and generally lower than available calculations.