Ohio University Qweak Status Report: 04/29/2004

• Study the position and energy distribution of elastic electrons that hit the Cerenkov bar (200cm x 16cm) at Z=530 cm, for no wall, 0.5m wall, and 1.0m wall cases. From the simulation results, the window size and position of 1.0m wall defined in our euclid file is fine, but some change need to be made for the window size and position of 0.5m wall.
  
  We found:
  
  
  1. No wall, 28.97k e- hit Cerenkov bar with E_mean = 1120 MeV.
     
     
  2. 0.5m wall, 28.83k e- hit Cerenkov bar with E_mean = 1115 MeV.
     
     
  3. 1.0m wall, 28.94k e- hit Cerenkov bar with E_mean = 1118 MeV.
     
     
  4. Position and energy distribution of electrons hitting Cerenkov bar
     
     
• Check the possible photon background that hits the beam pipe or other stuff and finally hits the Cerenkov bar, by changing the electron scattering angle (Theta) range from 4 - 12 degree to 0.32 - 71.49 degree, and running the simulation again with 1 million incoming electrons (only the ep elastic reaction).
  
  
  1. No wall, 4.73k photons hit Cerenkov bar at Z=530 cm, of which
     2.44k > 2 MeV
     2 MeV > 1.44k > 100 keV
     100 KeV > 0.85k > 10 keV
     
     Position and energy distribution of photons hitting Cerenkov, without wall
     
     
  2. No wall, there are 20.69k e- hitting Cerenkov bar.
     
     Position and energy distribution of electrons hitting Cerenkov, without wall
     
     
  3. No wall, there are 5 e+ hitting Cerenkov bar.
     
     
  4. No wall, 43.38k photons hit focal plane at Z=530 cm, but outside the Cerenkov bar, of which
     28.89k > 2 MeV
     2 MeV > 13.28k > 100 keV
     100 KeV > 2.21k > 10 keV
     
     Position and energy distribution of photons hitting outside the Cerenkov at Z=530 cm, without wall
     
     
  
  
• Fix a bug in my guideit input file, and recheck the photon survival rate of the trigger scintillator (210 x 23 x 1.0 cm) with two different light-guide geometry designs. One is a rectangular light-guide (5 x 23 x 7.62 cm) + cylinder light-guide (3 cm long, with a diameter of 3 inch), and the other is a fishtail shape light-guide. These two geometry designs are shown in fig. 1. Right now, we assume to use a 3 inch PMT, instead of a 2 inch PMT.
  
  
  1. When using rectangular shape light-guides, the photon rate is 7.3% for the PMT at close end, and 2.2% at far end. For 1.0 cm thick scintillator, and assuming 20% efficiency of PMT, we will have about 88 electrons at far end PMT and 146 electrons at close end PMT.
     
     
  2. When using fishtail shape light-guides, the photon rate is 5.3% for the PMT at close end, and 1.8% at far end. For 1.0 cm thick scintillator, and assuming 20% efficiency of PMT, we will have about 72 electrons at far end PMT and 106 electrons at close end PMT.
     
     
  According to above results, the rectangular light-guide is better than the fishtail light-guide. To avoid the PMT (which is around 30 cm long) being hit by the electrons passing through the shielding hut windows, we plan to add a triangle light-guide (45 degree) before the rectangular light-guide on both side of the scintillator, and move the rectangular, cylinder light-guides and PMT upward perpendicular to the scintillator.