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Accidental Coincidence Rates

Accidental Coincidence Rates. June 24, 2008. Window. Sci A. Probability of an open window = Rate A • Window length. Noise Hit. Sci B. Coincidence. Chance Coincidence. Window from yesterday = 100 ns Let rate of Sci A = 1 MHz Ex) Probability of an opening = 10 -7 • 10 6 = .1 = 10%

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Accidental Coincidence Rates

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  1. Accidental Coincidence Rates June 24, 2008

  2. Window Sci A Probability of an open window = Rate A • Window length Noise Hit Sci B Coincidence ChanceCoincidence Window from yesterday = 100 ns Let rate of Sci A = 1 MHz Ex) Probability of an opening = 10-7 • 106 = .1 = 10% ------------------------------------------------------------------------------------------------------------- Rate of an ACCIDENTAL Coincidence= Rate of Sci B • Probability of an Opening = RB • RA • Window

  3. Set window from yesterday = 100 ns Rate of scintillator A = 40 Hz Rate of a ACCIDENTAL Coincidence = RB • RA • Window Rate of scintillator B seen from yesterday= 100 Hz Rate of Accidental Coincidence = 100 Hz • 40 Hz • 10-7 = .04 Hz A fluctuation that small is obviously not seen on this graph

  4. Instead of a coincidence rate changing by .04 Hz, is it possible for the rate to fluctuate by 5 Hz? AC = RB • RA • Window RB = 5 Hz / (40 Hz • 10-7) ≈ 12 • 105 Hz 1.2 MHz is a much larger rate for B than was tested yesterday, but if it were to be tested, then one would see that the line for coincidence would deviate from the “plateau” by 5 Hz RA • RB = 5 • 107 Hz2

  5. Why does the coincidence rate rise? • Thermal Noise due to higher voltages • Efficiency = # coincidences / # scintillator hits • Noise in the scintillator, would cause an under-estimate of efficiency • Noise in the coincidence counter, would cause a false increase in efficiency • After-pulse can overlap with a single event, causing a false coincidence http://www.physics.uiowa.edu/~uakgun/FILES/Akgun_Nov04_HCAL_Meeting.pdf

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