Overview of the GlueX Tagger

and Photon Beamline.

Outline.

• Lay-out of Hall D/GlueX complex.

• Sketch of proposed beamline components.

• Basic beamline monitoring requirements.

• Photon polarimetry.

12 GeV CEBAF

CHL-2CHL-2

Upgrade magnets Upgrade magnets and power and power suppliessupplies

Enhance equipment in Enhance equipment in existing hallsexisting halls

add Hall D (and beam line)

Accelerator East Arc

Hall D Complex

Photon beam and experimental area

Located on the

East side off the

North linac

Tagger BuildingExperimental

Hall D

Solenoid-Based detector

Collimator

Coherent Bremsstrahlung

photon beam

Electron beam

75m

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

Moveable Active Photon Monitor

Photon Collimator cave

Concrete Housing

W Collimator

Sweeping Magnet

Steel Absorber

Concrete Block

Ni Collimator

Sweeping Magnet

Steel Absorber

Concrete Block

Moveable Active Photon Monitor

NMR

NMR

Exit Electron Beam (13.4° Bend)

Note.

1. Active Photon monitors-either a scintillating fibre array or a pair camera.

2. Distance from radiator to collimator ~80 m.

Active photon Collimator

Lead wall

Converter

Top View Photon flux Monitor

Magnet

Spectrometer Hall Wall

Detector array

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.

710

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.

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

presentations.