1. Simulation of electron beam halo in the Hall D tagger Richard Jones University of Connecticut GlueX collaboration meeting, Newport News, March 29-31, 2007

2. Review GlueX electron beam requirements were documented in gluex-doc-646. CASA has compared these requirements with the 12 GeV machine design and identified two places where more study is required: 1.electron beam halo 2.vertical electron beam emittance we asked for (based on early CASA model)now it looks more like (current CASA model) 2.5 mm  r 10 mm  r 2.8 mm  r 5.6 mm  r

3. GlueX collaboration meeting, Newport News, March 29-31, 2007 2-axis beam emittance spec. Vertical emittance directly affects the tagging efficiency, feeds into maximum rate compatible with tagging. The tagged beam parameters in the CDR assume  y is as good as the current CASA model says it can be! A detailed study is needed to show the impact of a larger vertical emittance on GlueX physics output. we asked for (based on early CASA model)now it looks more like (current CASA model) 2.5 mm  r 10 mm  r 2.8 mm  r 5.6 mm  r

4. GlueX collaboration meeting, Newport News, March 29-31, 2007 New results on halo issue CASA has made available new results from a ray-tracing simulation of electrons in the 12 GeV machine.

5. GlueX collaboration meeting, Newport News, March 29-31, 2007 GlueX sensitivity Original estimate (July, 2006) was based on some brutal assumptions regarding the shape of the halo. 1.uniformly distributed out to r = 25 mm 2.same energy, direction distribution as core beam Criterion was halo-related backgrounds in the tagging counters should contribute <1% to their rates. Result: CASA estimate: 3 · 10 -5 beyond ±5 mm boundary. 10 -5 beyond the 5  ellipse

6. GlueX collaboration meeting, Newport News, March 29-31, 2007 A new GlueX MC simulation CASA has now provided an estimate for the shape of the halo at the Hall D radiator crystal. Tasks for extracting a new tagger bg estimate: 1.create a 5-dimensional model for the halo 2.implement the model in a MC generator 3.couple the generator to the tagger simulation and run 4.extract normalized hit rates in the tagging counters f(x,y,p x,p y,p z )

7. GlueX collaboration meeting, Newport News, March 29-31, 2007 3 scenarios machine element alignment error:  0.3 mm (very good)  0.6 mm (OK)  1.0 mm (not good)

8. GlueX collaboration meeting, Newport News, March 29-31, 2007 3 scenarios actual measurements of transverse profile of the 6 GeV beam (Hall C, 5  a)

9. GlueX collaboration meeting, Newport News, March 29-31, 2007 3 scenarios main consequence of misalignment is more halo 1.central core beam size is unchanged. 2.shape of the halo distribution is unchanged.

10. GlueX collaboration meeting, Newport News, March 29-31, 2007 3 scenarios main consequence of misalignment is more halo 1.central core beam size is unchanged. 2.shape of the halo distribution is unchanged.

11. GlueX collaboration meeting, Newport News, March 29-31, 2007 3 scenarios main consequence of misalignment is more halo 1.central core beam size is unchanged. 2.shape of the halo distribution is unchanged.

12. GlueX collaboration meeting, Newport News, March 29-31, 2007 Compare “data” with model MC data from CASA ray-tracing simulation xy projection of 5d halo model (this study)

13. GlueX collaboration meeting, Newport News, March 29-31, 2007 Compare “data” with model MC data from CASA ray-tracing simulation x  x projection of 5d halo model (this study)

14. GlueX collaboration meeting, Newport News, March 29-31, 2007 Compare “data” with model MC data from CASA ray-tracing simulation y  y projection of 5d halo model (this study)

15. GlueX collaboration meeting, Newport News, March 29-31, 2007 Comparison in projections MC data from CASA for the 0.3mm case GlueX model derived for the 0.3mm case

16. GlueX collaboration meeting, Newport News, March 29-31, 2007 Comparison in projections MC data from CASA for the 0.3mm case GlueX model derived for the 0.3mm case

17. GlueX collaboration meeting, Newport News, March 29-31, 2007 What has changed? truncation at r = 1.2 cm main change: truncation at r = 1.2 cm (m)

18. GlueX collaboration meeting, Newport News, March 29-31, 2007 What has changed? truncation at r = 1.2 cm main change: truncation at r = 1.2 cm

19. GlueX collaboration meeting, Newport News, March 29-31, 2007 Results for 0.3 mm scenario

20. GlueX collaboration meeting, Newport News, March 29-31, 2007 3 scenarios factor of ~4 each step