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    User name R. Feuerbach

    Log entry time 13:44:11 on March 20, 2006

    Entry number 167590

    This entry is a followup to: 167525

    keyword=BB elastic electron trigger efficency is 50%

    There were a couple of errors in the referenced analysis, so below is the line of reasoning for calculating the trigger efficiency: 

    N3 = number of T3-only triggers = Ni*eS*eC*(PS-1)/PS
N2 = number of T2-only triggers = Ni*eS*(1-eC)/PS
N23= both T2 and T3 fired evts  = Ni*eS*eC/PS
    where Ni is the "pristine" number of elastic events (needed from a calculation), eS is the single-arm (BB) trigger efficiency, eC is the coincidence trigger efficiency (prob. of detecting proton in the ND), and PS is the prescale factor for T2 events. We're assuming the prescale for T3's is 1. I'm also neglecting the livetime contribution, since it will simply scale up the efficiency.

    In 167520 we found eC=26%. Given: 

    N3 = 9334
N2 = 2601
N23= 1043
and Ni = 73000  (from a calculation neglecting radiative effects and with
rough geometrical acceptances).

    Solutions for eS are: 

    eS = (N2 + N23)*PS/Ni
   -> eS = 0.499

eS = N3/(eC*Ni) * PS/(PS-1)
   -> eS = 0.526

eS = (N3 + N2 + N23)/Ni * 1./(eC*(PS-1)/PS + 1/PS)
   -> eS = 0.518

    So, NOT correcting for livetime (~20%?) or radiative effects, we are getting an electron-detection efficiency from run 2485 of ~50%.