Eurotag

Development of the European Tagged photon facilities.

Spokesperson: Ken Livingston, Glasgow

url: www.nuclear.gla.ac.uk/~kl/Eurotag

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 facilitiesImprovements 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 beamline Profile of MAMI photon beam

Coherent Brem. Photon Beam1st 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 peak coherent peak above peak

PolarimetryCoh. Brem Calc. (ANB/MCB Tuebingen) Polarimeter based on e+,e- production

Triplet productione+

e-

e+

Pair productione+

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