1. pe Collection Efficiency in CF4 Revisited HBD Meeting 04/15/08 B.Azmoun, A.Caccavano BNL

2. Set-Up VUV Beam from Spectrometer Beam SplitterMesh-CsI plane PC Monitor PMT Vessel: Vac or Gas Collect pe’s in “parallel plate” config— drift pe’ from PC to mesh—not into GEM holes PMTMonitor allows a correction for changes in lamp intensity Collection Efficiency is defined as the ratio of PC current at a given field to the max (plateau current) in Vac The plateau current is reached quickly in Vac

3. Coll. Eff.Vs Wavelength Monte Carlo Simulation J.Escada et al Collection efficiency f in CF 4 for photoelectrons emitted from a CsI photocathode irradiated with a continuous VUV Hg(Ar) lamp with a spectrum peaked at 6.7 eV (185 nm). A. Breskin, et al L. Coelho, et al J.Escada et al Real Data For the parallel plate config. Illustrated, in CF4, the Coll. Eff. doesn’t reach 100% even at relatively high field and the plateau is not perfectly flat The Coll. Eff. exhibits a wavelength dependence: smaller wavelengths suffer greater losses at a given field  not good for HBD Data and MC simulation agree relatively well BNL and Univ. of Coimbra data agree reasonably well

4. QE in CF4 Loss in pe Coll. Eff. Is reflected in lower QE in CF4 gas Gas Transmittance was measured simultaneously during QE measurement and was nearly 100% A wavelength scan w/ dV(DG)=300V shows the plateau value of the coll. Eff. across a wide range in wavelength

5. Reproducibility Most of the results presented were performed several times in the past and show very reproducible quantities

6. Integrated pe yield CsI QE folded into Cherenkov yield calc (also corrected for mesh and GEM trans.) Vac  36.6pe’s (110-200nm) CF4  27.2pe’s (110-200nm)—in this case used simple linear fit to QE data 27.2 pe

7. Applicable to HBD? D-1: Calculations performed by the simulation software, MAGBOLTZ Reference: S. Biagi, Nucl. Instr. and Meth. A421 (1999) 234 Fig. 1. Electron scattering cross- sections in Ar, Ne and CF 4 used in the Monte Carlo simulation: elastic momentum transfer (σ m ), vibrational excitation (σ ν4, σ ν3, σ νind ), electron attachment (σ a ), dissociation (σ d ), excitation (σ exc ), and ionization (σ ion ). J.Escada et al ~0.15mm 1.5mm If pe losses are similar over distances which differ in scale by an order magnitude, then all losses must happen very early in pe’s trip through gas—need detailed simulation which takes into account all interaction cross sections as pe traverses gas