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 ..... 12GeV 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!

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?

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.”

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

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.

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

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

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.