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Compton (and other) Issues
HAPPEX III
• Electron Analysis is already good enough.
• Photon integration as test.
• Photon counting analysis should be good.– Fix present analysis– Taka data at different beam rates to study
rate effectsSee analysis talk
Compton must integrate at 850 MeV
• Serious accidental issues now seen at an energy of 3 GeV
• Lineshape is an issue
• Both problems much worse at 850 MeV
See analysis talk
Spectra atlow energy
Low energy spectrahave a very complex shape.Large light output doesn’t
help.
Noise with Integration
• Need pulses near saturation.
• Flip helicity at 120 Hz or more?
• Pedestal noise complex.
Need Linearity with Known Small Corrections
• Electromagnetic MC shows linearity
• Photo-Neutron production at ~8 Mev is a potential of few % nonlinearity.
• Need Monte Carlo of neutron production
• How big are systematics
• Can we design a feasible test (straightforward test to 1% subject to systematics.)
Linearity
Light output of detector
• Need just enough for statistics;>10PE’s/Compton edge event.
• Spectrum has messy shape at low energy.
Speed of Detector Response
• Must be fast for 3 GeV photon counting analysis to keep accidentals low
Cavity and Stripline Studies
4ax 4bx
C2x C3x
Positions measured and computed from Dithering
4ax 4bx
C2xC3x
Positions computed by regression(One coefficient has the wrong sign.)
There is awaist at 4bx
with a width nearthe electronic
noise level
Explanation
<DMi>
<Mi2>
Typical Regression coeficient
<Mi2>=<(Mi
t+δ)2>=<(Mit)2>+<δ2>
Uncorrelated noise reduces coefficients
Need correlated noise to explain data
<MiMj>=<(Mi+δi)(Mjt+δj)>=<Mi
tMjt>+<δiδj>
Electronic noise222CEBC
222BPMEBBPM
222CEBPMEBPMC
If σB ~ σE, electronic and beam noise can be unfolded(without large subtraction in quadrature.)
Regression and dithering give different results:Regression is unreliable
Dithering implies that both have ~1 micron noise
Correlations probably invalidate regression analysis
Interpretation
• Correlated noise is significant noise limit.
• May be due to bandpass of instrumentation!
• Increases helicity reversal might help.
• Need more analysis (LUMI with both cavities and BPM’s?)