JRA3 Eurotag report, Dec 2005 1
EurotagDevelopment of the European tagged photon facilities.
Spokesperson: Ken Livingston, Glasgow
Members: Glasgow, Bonn, Giessen, INFN, Lund, Mainz, Tuebingen, Kharkov, JLab
Award: 600k€
Project Status:
Manpower All EU funded posts are now filled: 7 postdocs for > 11 man years
Workshop A 2 day workshop is organised for March 2006, Glasgow.
Timelines On target ( averaged over 6 sub-projects )
Dissemination Web site: www.nuclear.gla.ac.uk/~kl/Eurotag …. needs updating.
Internal reports, conference proceedings
JRA3 Eurotag report, Dec 2005 2
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:
Can Axial Quasi-channeling be used as a source of high energy polarised photons PRELIMINARY RESULT NO!
2D photon beam profile detector
JRA3 Eurotag report, Dec 2005 3
Beam profiler (Glasgow)
1mrad
Prototype detector in MAMI beamline Profile of MAMI photon beam
JRA3 Eurotag report, Dec 2005 4
Coherent Brem. Photon Beam1st Measurement of 2D photon enhancement for coherent bremsstrahlung. D. Glazier, Glasgow
Coh. edge at 200Mev, MAMI @ 855MeV
Data already in good agreement with
Monte-Carlo (MCB, Tuebingen)
Previously only photon energy spectrum
Now good data set with 2d photon dist.
Currently being used to improve Coherent
Bremsstrahlung models under Eugotag
(P. Grabmayr, Tuebingen).
Paper currently in preparation
On coh. peak Below coh. peak
JRA3 Eurotag report, Dec 2005 5
PolarimetryCoherent Bremsstrahlung Calculation (eg. Tuebingen)
Polarimeter based on e+,e- production
Triplet productione+
e-
e-
High analysing power ( > 50% )
Low cross-section, low energy recoil e
Tested (GWU) – only 3% analysing power
Pair production
e+
e-
Analysing power 22%
Higher cross-section
Tested (SC/Jlab) ~ 22% analysing power
Used successfully, needs only photon tagger
Many free parameters, > 5% systematic error
How to detect the pair (or triplet)
Magnetic spectrometer Microstrip detector
JRA3 Eurotag report, Dec 2005 6
Prototype Polarimeter (Bonn)Big contribution for non-EU members:
Kharkov Monte carlo simulations of Pair and Triplet polarimetry solutions (with Bonn)
Jlab Recent results and analysis of polarimeter for g8b (see below)
PRELIMINARY
J.Santoro, CUA
Asymmetry from Si
Microstrip detectors.
Average over full
Photon energy range
Peak > 90% pol.
Aim: Build a prototype polarimeter based on simulations and experience from JLab.
Small, portable, in-beam, fast (ie better than 5% in order of minutes)
K.Livingston, Glasgow