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Evaluation of WALTA’s CASA counters

Evaluation of WALTA’s CASA counters. WALTA Summer 2004 workshop Toby Burnett. Methodology. Study data Form a hypothesis for a model from a subset Check it against other similar data If OK: use as a prediction for new data Otherwise: modify (or abandon) hypothesis.

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Evaluation of WALTA’s CASA counters

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  1. Evaluation of WALTA’s CASA counters WALTA Summer 2004 workshop Toby Burnett

  2. Methodology • Study data • Form a hypothesis for a model from a subset • Check it against other similar data • If OK: use as a prediction for new data • Otherwise: modify (or abandon) hypothesis

  3. The data: singles (noise+signal) and signal vs. threshold • Use the UW muon telescope to define a clean muon beam; place CASA counter on top CASA A QNET card UW muon telescope B C UW Configuration: HV=1900 VA,B,C thresholds: 100, 200, 250 mV

  4. QNET setup, procedure • Channel 0,1,2 connected to A,B,C • Channel 3 to the CASA counter under test • Use scalars to measure rates for singles of each of 4 counters, and 4-folds • Adjust threshold, and measure rate for ~2500 triggers (2% statistics). Record threshold, singles rate on chan 3, 4-fold rate

  5. Verification of the geometry, setup • Move the counter under test by 5 cm in any direction: no change in 4-fold rates. Telescope CASA

  6. The data: note log-log plots

  7. Tentative observations • Singles rate is a power law (v is threshold voltage) • Signal rate approaches a constant at low threshold, falls off like a power law

  8. Initial Model Hypotheses • The exponent in the power law is universal • The signal and noise power law exponents are the same • The signal/noise ratio does not depend on the HV setting: changing the HV only changes the gain

  9. Model functions • Background: pure power law • Signal Note: v is threshold in mV, A the rate in Hz, v0 a reference So, how does it work?

  10. Apply to 1.25 kV 10-stage tube data Parameters: =1.8v0=40 mVAS=20 Hz AN=123Hz

  11. Checks • Apply to other data sets • Do TOT distributions agree with the model?

  12. Possible Implications, extensions • Simplified plateau procedure: measure enough points to determine parameters • Requires valid measure of the signal rate • Can predict efficiency vs. noise for any threshold given An/As and t0 • This is empirical: can one understand the power law exponent

  13. Differential, according to model

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