1. Compton counting photon analysis
Recent activity:
Found and fixed statistical bug.
Improved stability with better energy behavior of response function.
Investigated χ2 and time variation.
Monte Carlo study of pileup's effect on cut dependence (Zafar Ahmed).
Spectrum fit quality, absorber effects.
22 Jul 2008
R. Holmes / Compton counting photon analysis

2. Why we learn statistics
Asymmetry nonlinear in N+, N- -- error propagation bad when N± small.
Bad averages! Fix: sum pairs before doing asymmetry. Big slopes at high E are gone.
22 Jul 2008
R. Holmes / Compton counting photon analysis

3. χ2, time variation of polarization
22 Jul 2008
R. Holmes / Compton counting photon analysis

4. R. Holmes / Compton counting photon analysis
Cut dependence
22 Jul 2008
R. Holmes / Compton counting photon analysis

5. R. Holmes / Compton counting photon analysis
Accidentals
Monte Carlo: Accidentals (pileup) induce cut dependence.
3 causes: RF distortion, calibration distortion, high asymmetry. RF distortion dominates.
Effect is ~ ½ what we see.
Truncation of RF fit range greatly reduces cut dependence in Monte Carlo.
Truncation does not reduce cut dependence in data!
22 Jul 2008
R. Holmes / Compton counting photon analysis

6. Response function distortion
22 Jul 2008
R. Holmes / Compton counting photon analysis

7. R. Holmes / Compton counting photon analysis
Absorber effects
These differences
are significant
Absorber correction doubles cut dependence!
22 Jul 2008
R. Holmes / Compton counting photon analysis

8. R. Holmes / Compton counting photon analysis
Spectrum residuals
10x larger with absorber correction!
22 Jul 2008
R. Holmes / Compton counting photon analysis

9. R. Holmes / Compton counting photon analysis
RF width vs time
22 Jul 2008
R. Holmes / Compton counting photon analysis

10. R. Holmes / Compton counting photon analysis
Ydet vs time
Looks like an alignment problem
22 Jul 2008
R. Holmes / Compton counting photon analysis

11. R. Holmes / Compton counting photon analysis
Open questions
Something wrong with absorber correction?
Misalignment?
What happened late in the run?
Why does RF fit range truncation not fix cut dependence in data?
Can we find good canaries for problems?
What are the sizes of our systematics?
22 Jul 2008
R. Holmes / Compton counting photon analysis