Measurement of the Gerasimov-Drell-Hearn integrand for proton and deuteron from 200 to 1400 MeV

TL;DR

This study presents new high-precision measurements of the helicity-dependent cross sections for protons and deuterons from 200 to 1400 MeV, validating the GDH sum rule and enhancing data quality for nucleon studies.

Contribution

It provides the first detailed, high-resolution data for the GDH integrand over a broad energy range, enabling improved theoretical modeling and neutron information extraction.

Findings

Confirmed the GDH sum rule for proton, neutron, and deuteron.

Expanded the quantity and quality of helicity-dependent cross section data.

Provided a benchmark for theoretical models of nucleon structure.

Abstract

New data for the total inclusive helicity-dependent cross section for the proton and deuteron were obtained in the photon energy interval 200-1400 MeV. The experiment was performed at the A2 tagged-photon facility of the Mainz Microtron (MAMI) using a circularly polarized photon beam and longitudinally polarized proton and deuteron targets. The reaction products were detected using the large-acceptance Crystal Ball/TAPS calorimeter, which covers 97% of the full solid angle. These new results, obtained with fine energy binning, significantly expand both the quantity and the quality of the available data for these observables and enable a detailed comparison with state-of-the-art theoretical calculations. From the combination of the results for the deuteron and the proton, important information could also be extracted for the free neutron. Based on these data, and using existing models to evaluate the missing contributions from unmeasured photon energy regions, the validity of the Gerasimov-Drell-Hearn (GDH) sum rule has been verified for the proton, the neutron, and the deuteron. These new data provide a precise experimental benchmark for theoretical models used to study nucleons, both in their free state and when embedded in the nuclear medium.