A Compact Pair Polarimeter and Spectrometer

The measurement of polarisation ovservables in hadron physics can provide detailed information about the excited stated of baryons and mesons. A programme of such measurements has been running at the world's major photon beam facilities for several years and has already produced execellent, and well publicised, results. These experiments require highly polarised beams and targets with precisely known properties. In particular, for linearly polarised photon beams, the degree of polarisation needs to be known with as much precision as possible. Recent improvements in luminosity and data taking rates have meant that is often the limiting systematic error in an experiment. This proposal aims to solve the problem by developing a new polarimiter which will be capable of measuring the degree of linear polarisation to better that 2% systematic error, by measuring the asymmetry in the orientation of e+e- pairs produced as the photon passes through a thin converter foil. The design is a compact, modular system based on Halbach dipole cylinders (permanent magnets) and TimePix3 pixel detectors. It is low cost, with minimal readout infrastructure and can be configured for any of the current photon beam facilities (MAMI in Mainz, ELSA in Bonn and CLAS and GlueX in Jefferson Lab, Virginia).

This proposal would have direct impact for hardon physics photon beam facilities, listed below:

ELSA in Bonn, Germany
MAMI in Mainz, Germany
CLAS at Jefferson Lab, USA
GlueX at Jefferson Lab, USA

By upgrading their polarimety based on the prototype developed in this project they would see a increase in the precision of polarisation measurements. This would have an strong impact on the international hadron spectrosopy research programme which uses partial wave analysys to disentangle the spectrum of excited states of baryons and mesons. That would be relected in high quality publications with leading UK authors.

Further afield, the compact, modular, nature of the design would make it potentially applicable in any situation which requires flux monitoring and polarimetry with medium energy resolution. This could include Wakefied acelerators (eg SCAPA), laser backscattering facilities (eg ELI) and space based applications.