Ohio University Qweak Status Report: 04/01/2004

• Determine the angle between the central ray of the elastic electrons and the beamline by looking at the X projection of the electron envelop at Z =330, 380, 430, and 530 cm and fitting X_mean as a function of Z position. Here, we assume the Cerenkov bar being located at Z=530 cm normal to the central ray, the trigger scintillator at Z=520 cm perpendicular to the beamline, and the region 3 DC chamber will be around 100 cm long along Z direction. The angle between the central ray and beamline is 21.4 +/- 0.5 degree.
  
  
  1. Linear fit to determine the angle between the central ray and beamline
     
     
• Study the affect to elastic electron yield when put in a shielding wall in front of the region 3 chamber, and how well the wall can reduce the background (photons and positrons ) by changing the wall thickness from 50 cm to 100 cm. The back face of the shielding wall is fixed at Z=430 cm, which is a few cm before the region 3 chamber. A window is opened in the wall to let the elastic electrons passing through. The size of the window is determined from our study of electron envelop at the corresponding Z positions.
  
  
  1. Electron envelop before and after the window
     
     
  2. Photon envelop before and after the window
     
     
  
  What we learned from our studies:
  
  
• With a 50 cm thick shielding wall (having window), there are 28.40k elastic electrons passing through the window and hitting the Cerenkov bar (200 cm x 16 cm). Also, there are 6.18k photons, and 121 positrons hitting the Cerenkov bar.
  
  
• With a 100 cm thick shielding wall (having window), there are 28.33k elastic electrons passing through the window and hitting the Cerenkov bar. Also, there are 6.17k photons, and 67 positrons hitting the Cerenkov bar.
  
  
• Without a shielding wall, there are 28.4k elastic electrons hitting the Cerenkov bar. Also, there are 3.82k photons, and 18 positrons hitting the Cerenkov bar.
  
  
• With a suitable window, the thickness of the wall will not affect the elastic electron yield we may get. However, the background (photons and positrons) is increased when put in a shielding wall. On the other hand, a 100 cm wall is better than 50 cm wall to reduce the photon and positron background.