Overview of the GlueX Tagger and Photon Beamline.

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 CEBAF add Hall D (and beam line) Upgrade magnets and power supplies CHL-2 Enhance equipment in existing halls

4. Accelerator East Arc Hall D Complex

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

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

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

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

9. Basic Beamline Monitoring Requirements. • 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. • Incident electron beam direction and position (2 cavity position monitors upstream of radiator). • Photon beam direction and position ( active collimator, 3 active photon monitors). • Absolute photon flux ( lead-glass detector/pair spectrometer). • 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.