1. HBD Operation in Run 9 Thomas K Hemmick for the HBD Crew

2. HBD Improvements Reconstruction of HBD should improve voltage holding (does). Other considerations should improve light yield: –Improved gas transparency. –Precision Reverse Bias. All of these seem at first look to be achieved.

3. (2.5hrs. of flow thru cells) HBD-Ar @ 2.25lpm (straight-through mode, no scrubbing) HBD-CF4 @ 4.5lpm (Recirculation mode, incl. scrubbing) Transmission Scans

4. “ Traditional” GEM operation charged particle or photon primary ionization HV Mesh drifts ionization trail towards GEM stack Usually operated in Ar/CO2 ~300-400V across GEMs Mesh drifts ionization trail away from GEM stack, but allows Cherenkov photons Operate in CF4 - radiator and avalanche gas ~450-550V across GEMs Hadron Blind GEM operation ~350nm CsI primary ionization HV photo electron Reminder of HBD Principal

5. E-Field Line Directions Forward BiasReverse Bias Lines go to mesh Lines go to pad Lines go to GEM bottom In this simulation… electrons were created at the surface of the GEM. electron path follows E-Field lines recorded PE’s final destination. Reverse Bias (-30V): most (~91%) e’s from the GEM surface end up on pads. ~3% are swept up to mesh. ~6% lost to GEM bottom. note: field line destinations and actual charge destinations are different due to diffusion and avalanche. Line density does NOT represent field strength!

6. E-Field Line Directions Reverse Bias For an intuition of what different negative drift fields look like… notice that “reverse bias” doesn’t turn on immediately Lines go to mesh Lines go to pad Lines go to GEM bot Line density does NOT represent field strength!

7. Experimental results Hadrons (actually 55 Fe) drop suddenly in efficiency as bias goes reverse. Photon-electrons fall off slowly with increasing reverse bias. HBD will operate best when placed “just barely” into the reverse bias mode. Since voltages are roughly 4000 V, need 0.1% precision to get bias correct to 4V!!! 55 Fe Scintillation

8. Spectra in Beam Spectra show two components: –Single Scintillation Electrons (expo) –MIP (Landau) Scintillation MIPs FORWARD REVERSE

9. Goal List for HBD Gain Calibration (Standalone) : –Observe scintillation signal in every channel. –Fit scintillation slope to get gain. –Adjust voltages to get nearly uniform gain. –DONE (better than 10%...WOW) Forward/Reverse threshold (standalone): –Change bias step-by-step. –Search for loss of MIP peak. –DONE (and we thought this would be hard) High Statistics Reverse Bias (tracking) –Determine Hadron Response. –Determine isolated electron response. –Determine “double” electron response. –NEXT UP…

10. DV Scan Color scheme RUN LINE COLOR BIAS 274058 Red +30V 059 Black 0V 060 Green -5V 061 Blue -10V 062 Yellow -15V 063 Magenta -20V

11. EN1 -15VEN2 -10V EN3 -15VEN4 -10V

12. EN5 -10VES1 =-10V red,black (0V)‏ green(-5V),blue(-10V), rest(-15V)‏ ES2 -10VES3 -15V

13. ES4 -10VES5 -10V

14. WN1 -10VWN2 -10V WN3 -10VWN4 -10V

15. WN5 -15VWS1 -15V WS2 -10VWS3 -10V

16. WS4 -10VWS5 -10V

17. Live Area There are several troubles. Minor: –Individual bad strips take away 0.8% of the live area. –Require access for resistor swap on 2 strips. Major: –ES1 (edge of acceptance) has the grid touching a shorted strip. –Unless “burning” works, this sector will not function. –5% of overall area.

18. Summary HBD seems to work well. Data that are forthcoming should show exact single & double electron performance. The upcoming dataset will provide the basis for estimating Run-10 performance to the PAC.