1. Jlab Status Report Eurotag Workshop, Sept 1st - 2nd 2008 Ken Livingston, University of Glasgow
CLAS, Hall-B
Tagged linear and circularly polarised photons
High polarization
Recent runs LH2 and LD2
Double polarization for strange channels
Photon Asym for pi, eta, eta', K*, vector meson channels in progress. 1st publication soon
Photon polarisation systematics – hard work
Cannot tag 11GeV!
GlueX, Hall-D GeV upgrade
“Dedicated” to tagged, linearly polarised photons to search for exotic hybrid mesons
Tagger design complete?
1uA beam will radiation damage crystals
Need many 20um crystals of ~5mm size!

2. Tools for coherent brem experiments.
Prediction tool.
What pol can be expected from given beam, crystal, collimator etc.
Eg. anb, mcb (Tuebingen)‏
+ various front ends.
Works very well as a tool for predicting polarization.
Used to determine approximate goniometer settings.
Eurotag Aim: to have a well defined place where latest version is available with manual.
Polarimetry: Also can be a very good polarimeter in right conditions.
Can a “real” polarimiter do better?

3. Software: alignment and setup
Alignment technique developed
Software tools available
Already the “industry standard”
Site independent. Used in
MAMI, Mainz
ELSA, Bonn
CLAS, Jefferson Lab
GlueX, Jefferson Lab
MAXLab, Lund
“A device called a goniometer tilts the diamond, much like a lady turning her hand to admire the sparkle of a new ring.”

4. Software: online control
Example from Jlab (land of the GUI)‏
Suitable for non-expert shift workers
Interacts via EPICS slow controls
Site independent ?
Not yet, but soon.
Difficult due to different DAQs

5. Polarimetry: The biggest challenge
Bremsstrahlung calculation.
Works well if peak “fittable” and stable.
But that's not always the case ....
eg. g8b and other Jlab expts.
Need alternative methods of polarimetry.

6. Polarimetry: from pair (e+,e-) production (or triplet)‏
Well described by QED, but experimentally difficult – small opening angle e+ e-
Pair production simulations by Kharkov group
Polarimeter built and tested at Sping8, recently tested at Jlab
Peak > 90% pol.
PRELIMINARY
K.Livingston, Glasgow
J.Santoro, CUA
Polarimeter to be based on Jlab design
Microstrip detectors, or pixel detectors (Atlas group)
Bonn student completed 10 months exchange in Glasgow now to be full time in Bonn.
Advantages.
QED “well understood”
Disadvantages.
Needs to be built.
Needs good calibration / simulation

7. Polarimetry: from hadronic or atomic reaction .. in your target
Use reaction with a known photon asymmetry
Can be high statistics
Very good relative monitor of polarization
Combined beam, target polarization.
Non-indpendent – depends on specific expt
Need very good systematics or calibration
Recent preliminary results from JLab (g8b)‏
Proton target
Back to back charge particles in Start Counter
Atomic or hardonic ?
Asymmetry from ~20mins DAQ data
Constant with E from 1.3GeV – 1.9GeV ?
Advantages.
It's there in your expt.
Disadvantages.
Maybe not “well understood”
Needs good calibration / simulation

8. What legacy can Eurotag leave for coherent brem expts
Diamonds
Selection, evaluation
Guidance, publication
Prediction tool
anb, mcb others (Bob ?)‏
Front ends
Manuals‏, publications
Setup, alignment, running tools
Stonehenge technique etc.
Manuals, publication
Polarimetry
anb, mcb
Design for a pair polarimiter.
Evaluation of other techniques based on known reaction in target.