Measurement of helicity dependence of single π0 photoproduction on deuteron

Federico Cividini

doi:10.1051/epjconf/201919902007

Abstract

The study of the properties of the baryon resonances gives essential constraints on models for nucleon structure. Pion-photoproduction is a powerful tool to excite the nucleon to an intermediate resonant state and, in combination with polarised beams/targets, plays an important role in the investigation of the nucleon resonances. Data for polarisation observables accessible using a polarised photon beam and/or polarised nucleon targets are scarce in many channels, especially in those involving a neutron target. A systematic measurement is performed at the Mainz facility by the A2@MAMI collaboration. This talk will focus on the experiment performed at the Mainz Microtron, using a circularly polarised photon beam and a longitudinally polarised deuteron target, in conjunction with the large acceptance Crystal Ball/TAPS detection setup. An overview of the status of the experiment will be given, together with the preliminary results of polarised cross section from deuteron and of the double polarization observable E for the single π0 photoproduction reaction from the quasi-free proton and quasi-free neutron.

Highlights

The nucleon gives the largest contribution to the visible mass of the Universe
Electromagnetic probes provide a powerful tool to access the internal structure of the nucleon and to study its resonances
Photoproduction reactions of single pseudoscalar mesons from the nucleon are described theoretically by 4 helicity amplitudes, which lead to 16 different experimental observables

Summary

Introduction

The nucleon gives the largest contribution to the visible mass of the Universe. Its internal structure, despite being intensively studied both from the experimental and theoretical point of view, is not yet fully understood. Electromagnetic probes provide a powerful tool to access the internal structure of the nucleon and to study its resonances. The new precise results on double-polarization measurements on the proton and on the neutron, obtained by the A2 collaboration, extend the available statistics, especially on the neutron, providing essential constrains on models of the nucleon structure.

Results

Conclusion