1. Overview of the GlueX Tagger and Photon Beamline.

2. Outline. Lay-out of Hall D/GlueX complex. Sketch of proposed beamline components. Basic beamline monitoring requirements. Photon polarimetry.

3. 12 GeV CEBAFCHL-2 Upgrade magnets and power supplies Enhance equipment in existing halls add Hall D (and beam line)

4. Accelerator East Arc Hall D Complex

5. Photon beam and experimental area Located on the East side off the North linac Tagger Building Experimental Hall D Solenoid-Based detector Collimator Coherent Bremsstrahlung photon beam Electron beam 75m GlueX Detector Hall Collimator Cave

6. GlueX Beamline Upstream of Spectrometer (i) Diamond +Goniometer Quadrupole Moveable Microscope 8.5 GeV <Eγ<9GeV Broadband Focal Plane 3GeV <Eγ<11.4GeV Electron Beam Current Monitor Electron Beam Dump Permanent Magnet Tagger Dipole Magnet Steel Absorber NMR Exit Electron Beam (13.4° Bend) Note. 1.Photon monitors-either a scintillating fibre array or a pair camera. 2.Distance from radiator to collimator ~80 m. Active photon Collimator Moveable Photon Monitor Photon Collimator cave Concrete Housing W Collimator Sweeping Magnet Steel Absorber Concrete Block Ni Collimator Sweeping Magnet Concrete Block Moveable Photon Monitor Lead wall Converter GLUEXDETECTOR HALLGLUEXDETECTOR HALL

7. Top View Photon flux Monitor Magnet GlueX Detector Hall Wall Detector array Moveable Microstrip Detector GlueX Beamline Upstream of Spectrometer (ii) GLUEXSPECTROMETERGLUEXSPECTROMETER COLLIMATOR CAVECOLLIMATOR CAVE

8. GlueX Beamline Downstream of Spectrometer Moveable Lead Glass Monitor Photon Beam Dump Active Photon Monitor GLUEXSPECTROMETERGLUEXSPECTROMETER

9. Basic Beamline Monitoring Requirements. 1.The electron beam intensity (current measuring cavity), tagger focal plane counting rate and the collimated photon flux (pair spectrometer) must be maintained at a ~1-2% ratio. If any one changes with respect to the others, re-tuning will be necessary. 2.Incident electron beam direction and position (2 cavity position monitors upstream of radiator). 3.Photon beam direction and position ( active collimator, 3 active photon monitors). 4.Absolute photon flux ( lead-glass detector/pair spectrometer). 5.Photon polarisation.

10. Photon Polarimetry. It is proposed to measure the photon degree of linear polarisation for ( Hz tagged rate on target measured by the microscope ) by: a) Indirectly. Comparing the shapes of the measured and calculated ratios - diamond /amorphous tagger focal plane spectra – over the complete energy range of the tagger. Both the ungated, and gated with photons passing through the collimator, measured focal plane spectra are required. The gating signal could come from the pair spectrometer. This is one reason why a broad band tagger is necessary.

11. b) Directly. Various techniques have been studied by Yerevan/Connecticut – 2 papers are in press. They make 2 recommendations. measure the azimuthal distribution of events from nuclear pair production with a Si strip detector triggered by the pair spectrometer, and measure hadronic asymmetries - distributions from production – using the GlueX spectrometer.

12. Details of the Photon Beamline and Tagging Spectrometer will be presented in the following presentations.