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?)