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Jlab Status Report Eurotag Workshop, Sept 1 st - 2 nd 2008 Ken Livingston, University of Glasgow

Jlab Status Report Eurotag Workshop, Sept 1 st - 2 nd 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

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Jlab Status Report Eurotag Workshop, Sept 1 st - 2 nd 2008 Ken Livingston, University of Glasgow

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  1. Jlab Status ReportEurotag Workshop, Sept 1st - 2nd 2008Ken 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!

  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.

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