First measurement of the helicity dependence of3He photoreactions in the Δ(1232) resonance region

Susanna Costanza

doi:10.1051/epjconf/20146606005

Abstract

The first measurement of the helicity dependence for several photo-reaction channels on 3 He was carried out in the photon energy range between 150 and 500 MeV at the MAMI accelerator (Mainz). The experiment used the large acceptance Crystal Ball spectrometer, complemented by charged particle and vertex detectors, a circularly polarised tagged photon beam and a longitudinally polarised high-pressure 3 He gas target. Results of the helicity dependent total inclusive photoabsorption cross section on 3 He and of both the unpolarised and polarised partial cross sections for the pion photoproduction channels γ 3 He → πX and for the γ 3 He → ppn channel, measured for the first time at MAMI, will be shown. They can also be found in [1].

Highlights

Sum rules are of particular interest for the study of the internal structure of the nucleon, in particular its spin structure
The first experimental check of the GDH sum rule for the proton was performed by the GDH collaboration jointly at the Mainz and Bonn tagged photon facilities in the photon energy range between 200
The cell was placed inside the central detector system, devoted to the detection of the reaction products. It was composed by the Crystall Ball (CB) NaI spectrometer, a large solid angle, highly segmented photon and hadron spectrometer, and it was complemented by the Multi-Wire Proportional Chambers (MWPCs), used to identify and track the charged particles, and by the Particle Identification detector (PID), used to discriminate between the charged and the neutral particles detected in CB

Summary

Introduction

Sum rules are of particular interest for the study of the internal structure of the nucleon, in particular its spin structure. One of this is the well-known Gerasimov-Drell-Hearn (GDH) sum rule [2, 3], which relates the nucleon anomalous magnetic moment κ, the spin S and the mass M to the integral of the helicity asymmetry of the total absorption cross section for circularly polarised photons on a longitudinally polarised nucleon target: IGDH =.

Experimental setup

Total inclusive cross section

Partial reaction channels

Differential cross sections

Conclusions