1. The Tagger Microscope Richard Jones, University of Connecticut Hall D Tagger - Photon Beamline ReviewJan. 23-24, 2005, Newport News presented by GlueX Tagged Beam Working Group University of Glasgow University of Connecticut Catholic University of America

2. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 2 Presentation Overview Design requirements Focal plane geometry 2D segmentation Scintillating fiber design

3. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 3 I. Design Requirements  spectrum coverage 70% - 75% in 0.1% steps  energy resolution 0.1% (9 MeV) r.m.s.  rate capability up to 500 MHz per GeV rates at 3  A on a 10 -4 radiator (10 8  /s)

4. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 4 Requirements: Channel Count energy resolution 1.channel width from energy resolution: rate limitations: 2.channel width from rate limitations: margins: 3.additional margins: 4 MeV = 4 MeV 2 MHz 500 MHz/GeV 9 MeV transverse segmentation OR, keep the channel width fixed at 9 MeV and introduce transverse segmentation 30% margins 100 energy channels

5. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 5 II. Focal Plane Geometry 1.Focal plane x coordinate is roughly linear in energy 2.Crossing angle is changing quite rapidly with energy 3.Microscope optimized for E  ~ 8 – 10 GeV nominal position limited mobility

6. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 6 III. 2D Segmentation What is the argument for measuring the out-of-plane scattering angle?   y 9 GeV 3 GeV collimator y y  This photon cannot get through the collimator but its electron still reaches the focal plane and produces a count there.  By reducing the acceptance of the tagging counters to a region part of the tagging efficiency lost through collimation is recovered. |  y | <  half-collimator (P  kick from crystal is negligible)

7. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 7 Vertical tagger coordinate scale  Monte Carlo test Hall D collimator detailed tagger optics quadrupole field on  tagging efficiency improved by 30%  impact on polarization negligible Size of one fiber

8. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 8 IV. Scintillating Fiber Design focal plane electron trajectory SiPM sensors scintillating fibers clear light fibers Design parameters Design parameters  square scintillating fibers  size 2 mm x 2 mm x 20 mm  clear light guide readout along electron direction  aligned along electron direction for reduced background sensitivity silicon photomultipliers SiPM devices  readout with silicon photomultipliers (SiPM devices)

9. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 9 Silicon Photomultiplier Fiber Readout  Excellent characteristics for this application: Fast timing (x2 faster than PMT’s) Dynamic range factor 1000-10000 Gain similar to phototube (10 6 ) Requires no HV (only ~50V bias) QE similar to PMT (higher in green, lower in blue)  Data reported by G. Lolos et.al.  Device  QE  QE 550 nm SiPM 0.3 60% 20% PMT 1.0 5% 5% 437 nm SiPM 0.3 45% 15% PMT 1.0 25% 25%

10. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 10 Silicon Photomultiplier Fiber Readout  Expected light yield for axial electrons:  One complete electronics chain per energy channel  Individual SiPM bias voltage settings under computer control  Conventional counting is possible by enabling all rows  Vertical alignment requirement is similar to that for collimator  total path length in scintillator: 2 cm  scintillation light emitted: 10 4 photons / MeV  fiber capture fraction: 5%   x quantum efficiency: 15% 300 p.e.

11. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 11 Summary resolution and rate requirements A design for the fine-grained region of the Hall D tagger hodoscope has been found which satisfies the resolution and rate requirements for the GlueX experiment. The design achieves a 30% improvement in tagging efficiency over conventional tagging by configuring the tagging counters as a non-defining collimator slit. longitudinally to the electron tranjectories Scintillating fibers oriented longitudinally to the electron tranjectories provide adequate light output for good timing and high-efficiency operation, while reducing their sensitivity to off-axis backgrounds. A conceptual design for the readout exists.

12. Richard Jones, Hall D Tagger- Photon Beamline Review, Newport News, Jan 23-24, 2006 12 Tagging spectrometer: two dipole design radiator quadrupole dipole 1 dipole 2 photon beam full-energy electrons focal plane  final bend angle:13.4 o  dipole magnetic field:1.5 T  focal plane length:9.0 m  energy resolution:5 MeV r.m.s.  gap width:3 cm  pole length:3.1 m  dipole weight:38 tons  coil power:30 kW