eurotag development of the european tagged photon facilities. spokesperson: ken livingston,...
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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
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