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HBD R&D update:

This update provides a summary of the main activities over the last 3 months, focusing on completing the proof of principle for the proposed HBD concept. Topics covered include measurements with cosmic rays, stability and cross-talk solutions, and hadron blindness suppression. The conclusion outlines future milestones and areas of study.

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HBD R&D update:

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  1. HBD R&D update: Itzhak Tserruya DC Upgrades meeting October 9, 2003

  2. Summary • Main activity over the last 3 months: complete the proof of principle of the proposed HBD concept: - Measurements with cosmic rays to demonstrate the expected yield of ~40 photoelectrons and the necessary hadron rejection factor of ~200. - Stability and cross talk problems solved.

  3. Cosmic trigger S1.S2.S4 • pth 3.8 GeV • 1.30 m long • rate  1/min C: CO2 radiator • 50 cm long • directly coupled to detector CF4 Radiator • triple GEM + CsI • test with Fe55, UV lamp,  Detector Box Cosmic ray tests: Experimental Set-up C S4 S1,S2

  4. Cherenkov response to S1.S2.S4 S1.S2.S4.C  mip S1.S2.S4.C  “electron” Cosmic ray tests: Experimental Set-up C S4 S1,S2

  5. Hadron Blindness: response to mip * Signal collected on a single pad ED = 1 KV/cm (“collection”) ED = -0.5 KV/cm (“repulsion”) Average amplitude dropped by a factor of ~2.5 and rate dropped by a factor of 12 Strong Hadron Suppression

  6. Hadron Blindness: response to “electrons” * Signal collected on more than one pad ED = 1 KV/cm (“collection”) ED = -0.5 KV/cm (“repulsion”) Signal = mip + Cherenkov photons Signal = Cherenkov photons All spectra calibrated into pe using the response to Fe55 x-rays, assuming 5.9keV x-ray produces 109 primary electrons in CF4 .

  7. Photoelectron yield vs. cosmic μ momentum Saturated npe ≈ 45!

  8. Conclusion and Outlook • I think that the proof of principle exists. • We still have a number of issues to study: - asymmetric operation of GEMs - HV segmentation - operate without pumping …. • Next milestones: - Monte Carlo simulations: can the HBD do the job alone? - Detector design

  9. Hadron Blindness (I): UV photons vs.  particles At slightly negative ED, photoelectron detection efficiency is preserved whereas charge collection is largely suppressed.

  10. CsI photocathode QE The most attractive option: • Transmissive photocathode • Relatively high quantum efficiency Very large bandwidth: 6 – 11.5 eV Very large N0 940 cm-1: 60 e in a 50cm radiator or ~40 pe taking optical transparency losses of mesh and GEM into account electron efficiency > 90%

  11. Powering scheme Overall Set-up Detector Box HV Independent powering of the mesh 50 cm long CF4 Radiator Am241 or Fe55 R D2 UV Lamp Mesh HV 1.5mm R GEM1 1.5mm R GEM2 R 1.5mm GEM3 R R 2mm 2R PCB Detector box (9 3x 3 cm2 pads) R = 10MW Resistive chain Powering of triple GEM Set-up

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