Beam-Induced Nuclear Depolarisation in a Gaseous Polarised Hydrogen Target

TL;DR

This paper investigates how intense bunched beams can cause depolarisation of spin-polarised hydrogen targets in storage rings, identifying conditions to avoid significant depolarisation effects.

Contribution

It provides experimental observations and an analytic model explaining beam-induced depolarisation resonances in gaseous polarised hydrogen targets.

Findings

Resonances observed with the HERA positron beam at DESY

An analytic model explains the shape and position of depolarisation resonances

Operational conditions identified where depolarisation is minimized

Abstract

Spin-polarised atomic hydrogen is used as a gaseous polarised proton target in high energy and nuclear physics experiments operating with internal beams in storage rings. When such beams are intense and bunched, this type of target can be depolarised by a resonant interaction with the transient magnetic field generated by the beam bunches. This effect has been studied with the HERA positron beam in the HERMES experiment at DESY. Resonances have been observed and a simple analytic model has been used to explain their shape and position. Operating conditions for the experiment have been found where there is no significant target depolarisation due to this effect.