Ohio University Qweak Status Report: 05/13/2004

• New trigger scintillator scheme
  
  
  1. The dimension of the scintillator is 210 x 23 x 1.0 cm, with a 45 degree triangular light-guide and a 3 cm long cylindrical light-guide on each side. The 30 cm long 3" PMT is perpendicular to the scintillator.
     
     
  2. According to the guideit simulation results of above design, the photon rate is 5.8% for the PMT at close end, and 1.8% at far end. For 1.0 cm thick scintillator, assuming 20% efficiency of PMT, we will have about 72 electrons at far end PMT and 232 electrons at close end PMT.
     
     
  3. Allena had sent the new scintillator scheme to the company asking about the price quote. Hopefully, we will have the first set of scintillator and light-guides arriving at JLab before July to begin the bench tests.
  
  
  
• Study to determine the shielding wall window size and position
  
  
  1. Firstly, we change the electron scattering angle (Theta) range from 4 - 12 degree to 0.32 - 35 degree, and run the simulation with 500k incoming electrons (only the ep elastic reaction) for both no wall and 1.0m wall cases. The results are shown in Fig.1 (electron) and Fig.2 (photon). Fig.3 (electron) and Fig.4 (photon) show the original positions where the "secondary" electrons and photons are coming from.
     
     
     1. No wall, 4734 photons hit Cerenkov bar at Z=530 cm, of which
        2788 > 1 MeV, and
        10 KeV < 1946 < 1 MeV.
        There are 21020 e- hitting Cerenkov bar with E_mean = 1122 MeV, of which 15 are "secondary" electrons.
        
        
     2. 1.0 m wall, 6107 photons hit Cerenkov bar at Z=530 cm, of which
        3756 > 1 MeV, and
        10 KeV < 2351 < 1 MeV.
        There are 21077 e- hitting Cerenkov bar with E_mean = 1121 MeV, of which 93 are "secondary" electrons.
        
        As shown in Fig.3 and Fig.4, there are significant amount of photons and "secondary" electrons generated at the edge of the shielding wall window.
        
        
  2. Secondly, we change the electron scattering angle (Theta) range back to 4 - 12 degree, and run the simulation with 100k incoming electrons (only the ep elastic reaction) for no wall case. Firstly, we have the whole spectrometer filled with air. Then, we have the spectrometer filled with helium gas. The results are shown in Fig.5 (electron) and Fig.6 (photon).
     
     
     1. When filled with air, 6359 photons hit Cerenkov bar at Z=530 cm, of which
        3782 > 1 MeV, and
        10 KeV < 2577 < 1 MeV.
        There are 28361 e- hitting Cerenkov bar with E_mean = 1121 MeV, of which 13 are "secondary" electrons.
        
        
     2. When filled with helium gas, 520 photons hit Cerenkov bar at Z=530 cm, of which
        321 > 1 MeV, and
        10 KeV < 199 < 1 MeV.
        There are 29388 e- hitting Cerenkov bar with E_mean = 1141 MeV, of which none is "secondary" electron.
        
        As shown in Fig.5 and Fig.6, using helium gas, instead of air, can reduce the photons and "secondary" electrons hitting Cerenkov bar.