Eurotag Development of the European Tagged photon facilities. Spokesperson: Ken Livingston, Glasgowurl: Upgrade to 250MeV New Coherent Brem New Tagger Crystal Barrel upgrade Coherent Brem. Crystal Ball Upgrade to 1.5GeV Upgrade of Tagger Upgrade of C. Brem Beam intensity x2 Lin. Pol 96% Members: Glasgow, Bonn, Giessen, INFN, Lund, Mainz, Tuebingen, Kharkov, JLab Bremsstrahlung facilities Improvements to provision of linearly polarised photon beams Award: 600k€

Linearly polarised photons Standard Technique: Coherent Bremsstrahlung Improvements to degree of polarisation: Better collimation from understanding 2D photon distrib. Improvements to polarimetry: Improve cbrem calculation. Build prototype polarimeter. New possibility: Axial Quasi channeling Investigate as possible source of high energy polarised photons by looking at 2D distrib of tagged photons 2D photon beam profile detector

Beam profiler (prototype) 1mrad Detector in MAMI beamlineProfile of MAMI photon beam

Coherent Brem. Photon Beam 1 st Measurement of 2D photon enhancement for coherent bremsstrahlung. D. Glazier, Glasgow Current Analysis: Investigation of quasi channeling from data taken in Mainz (Dec 04) Investigation of 2D strip detector for polarimetry Coherent peak at 300Mev, MAMI electron beam energy 855MeV below peakcoherent peakabove peak

Polarimetry Coh. Brem Calc. (ANB/MCB Tuebingen)Polarimeter based on e +,e - production Triplet production e+e-e+e- e+e+ Pair production e+e-e+e- High analysing power Low cross-section, low energy e difficult to detect Already tested (GWU) – 3% effective analysis power Analysing power 22%, higher cross-section Pair polarimeter for Jlab commisioned in 2 weeks (Jlab, S. Carolina – tested at Spring 8) Eurotag (Bonn) will build prototype pair polarimeter, based on experience from Jlab, simulations (Kharkov), 2D beam profiler tests (Glasgow). Aim: < 5% systematic error, Fast (minutes), in-beam measurement Used successfully, needs only photon tagger Many free parameters, > 5% systematic error