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