1. Tagging Near the End-Point Richard Jones, University of Connecticut GlueX Collaboration Meeting, Newport News, May 8-10, 2008 1.Current design capabilities 2.Limits of end-point detection 3.Can the microscope be moved there?

2. GlueX Collaboration Meeting, Newport News, May 8-10, 2008 2 Current design 50 individual scintillator paddles cover 9.0 – 11.4 GeV. 100% coverage above 9 GeV fixed array microscope

3. GlueX Collaboration Meeting, Newport News, May 8-10, 2008 3 Current design average tagger rate 40 counters average rate @ 10 8 maximum rate recent update: increase segmentation x2 200 MHz / GeV fixed array coverage 15 MHz / channel 22 MHz / channel

4. GlueX Collaboration Meeting, Newport News, May 8-10, 2008 4 Near the end-point limit Why stop at 11.4 GeV? 11.811.711.611.5 photon energy (GeV): 11.9

5. GlueX Collaboration Meeting, Newport News, May 8-10, 2008 5 End-point limits what is this cutoff? Do these low-energy electrons make it through the spectrometer? artifact from exit window flange

6. GlueX Collaboration Meeting, Newport News, May 8-10, 2008 6 End-point limits Do these low-energy electrons make it through the spectrometer?

7. GlueX Collaboration Meeting, Newport News, May 8-10, 2008 7 Can the microscope be moved there? nominal position limited mobility The fiber array has some flexibility, but…

8. GlueX Collaboration Meeting, Newport News, May 8-10, 2008 8 Conclusions Current fixed-array design covers up to 11.4 GeV. Supports concurrent running with microscope at full intensity – provided triggers exist that use it. The limit 95% E 0 was never carefully examined before. By just adding a few counters to the end of the existing array it could be extended up to ~ 11.7 Gev. Requires that the vacuum exit window be extended. The tagger pole gap effectively limits the minimum electron energy to E e > 300 MeV in the present geometry.