Update on Simulation Studies of the CEDAR Optics Helen Heath 9 th December 2009

Reminder (see N.Brook’s talk from August) Use Lau’s CEDAR simulation provide Cerenkov photons to current quartz window -> position(x,y,z) and direction(n x,n y,n z ) and wavelength Optical path simulation Use ROOT and its geometry manager 2

Z=646mm 3 Z=996mm

Parabaloidal “cones” 10mm depth25mm depth 4

Summary of results in August 10mm cone 82-87% photon reach PMT cathode 68-90% of photons reflected off cone reflect off PMT window 25mm cone 87-91% photon reach PMT cathode 29-67% of photons reflected off cone reflect off PMT window 5

Cone v Parabaloid Efficiency for photons to reach the PMT cathode v z position 6

Efficiency for different cone depths Shown for conical collection cones Note: there is little increase in efficiency one the cones are above 15mm in length The parabaloid is similar but the efficiency falls more quickly 7

Source of Losses Previous simulations assumed losses at surfaces due to 5nm roughness for mirror 10nm roughness for cones Look at cone roughness 8

Photon loss v cone depth z=646 9

Escapees 10

Photon loss v cone depth z=646 11

Photon loss v cone depth z=646 12

Summary of Efficiency Studies Dominant contributions to the photon loss are Photons escaping the system for depth<7mm Reflection from the PMT surface 7mm<depth<~10mm Beyond 10mm the loss at the cone surface may become the dominant contribution but it increases slowly above ~15mm 13

Photon distributions at PMT Nick’s studies observed a double peak in the photon angle at the PMT. Confirmed to be photons reflected from the cone and those that enter directly (see next slide) Also noted that the distribution across the PMT face is different for these two cases 14

10mm cone, photon angle to PMT face. Red photons not reflected from cone, blue photons reflected from cone 15

25mm cone, photon angle to PMT face. Red photons not reflected from cone, blue photons reflected from cone 16

17 25mm cone, photon position at PMT face. Red, photons not reflected from cone, black photons reflected from cone

Efficiencies for photons from Pions photons 25mm cone Efficiency 0.10% for all z 18

Future plans To look at the muon halo Feed in any mechanical design constraints 19