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
Top View Photon flux Monitor Magnet Spectrometer Hall Wall Detector array Moveable Microstrip Detector GlueX Beamline Upstream of Spectrometer (ii)
GlueX Beamline Downstream of Spectrometer Moveable Lead Glass Monitor Photon Beam Dump Active Photon Monitor
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 constant 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.
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.
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.
Details of the Photon Beamline and Tagging Spectrometer will be presented in the following presentations.