The Gerasimov-Drell-Hearn sum-rule with nuclear targets

TL;DR

This paper explores how the Gerasimov-Drell-Hearn sum rule is affected by nuclear medium modifications, predicting enhancements and shifts in resonance properties that can be tested with polarized nuclear targets.

Contribution

It analyzes the GDH sum rule for nucleons in nuclear media, highlighting expected modifications in resonance masses and magnetic moments, and suggests experimental tests with polarized nuclear targets.

Findings

Enhanced GDH sum rule contributions due to medium effects

Shift of the $$ resonance to lower energy in nuclear medium

Potential for experimental verification with polarized nuclear targets

Abstract

Hadron properties are modified when the hadron is embedded in a nuclear medium. Here we discuss the Gerasimov-Drell-Hearn, GDH, sum rule for polarised photoproduction from a polarised nucleon within a polarised nuclear target. Strong enhancement is expected with the suppression of the proton and nucleon resonance masses and enhancement of the proton's anomalous magnetic moment in medium. This could be tested in polarised photoproduction experiments with interesting targets being polarised deuterons, $^3$He, $^6$Li and $^7$Li. The largest contribution to the GDH sum rule comes from the $\Delta$ resonance excitation. In existing data with polarised deuterons and $^3$He the $\Delta$ excitation is shifted to slightly lower energy when compared to model predictions where the $\Delta$ is treated with its free mass.