Trigger Sensitivity with Dual Mirrors

The dual mirror technique has been proposed as a method to reduce the cost of achieving a small pixel size for a prescribed S/N sensitivity. As a byproduct, the trigger sensitivity is enhanced. This is an important consideration as moonlight threatens to reduce the detector's trigger aperture. The uorescence detector shower resolution depends critically on good angular resolution as well as the signal-to-noise ratio (S/N) as de ned in the Design Report (DR). Important design parameters are the mirror diameter D and the pixel angular width . Since S/N D/ , the signal-to-noise ratio can be increased by increasing D, decreasing , or both. For the Superman 3-eye con guration without dual mirrors, the cost optimization leads to a pixel size which is too large to allow good angular resolution. The dual mirrors technique was proposed [1] as a way to achieve the required small (virtual) pixel size with half as many PMT's as would be needed with the single mirror method. [Note: For the customary single mirror con guration, a \virtual pixel" is just a PMT. With dual mirrors, \virtual pixel" refers to the overlap of two PMT's.] Mirror diameters must increase to retain the same S/N as would pertain to a single mirror system of equal virtual pixel size. Suppose a maximum allowable virtual pixel angular width 0 is dictated by angular resolution criteria, and a minimum S 0 /N 0 is speci ed by X max resolution criteria. One can then calculate the mirror diameter D 0 which would be needed using the traditional single mirror method. What mirror diameter D is needed for each of the dual mirrors to