Compton and other Issues

1
Compton (and other) Issues
2
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
  effects

See analysis talk
3
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
4
Spectra atlow energy
Low energy spectra have a very complex
shape. Large light output doesnt help.
5
Noise with Integration

• Need pulses near saturation.
• Flip helicity at 120 Hz or more?
• Pedestal noise complex.

6
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
7
Light output of detector

• Need just enough for statisticsgt10PEs/Compton
  edge event.
• Spectrum has messy shape at low energy.

8
Speed of Detector Response

• Must be fast for 3 GeV photon counting analysis
  to keep accidentals low

9
Cavity and Stripline Studies
There is a waist at 4bx with a width near the
electronic noise level
Positions measured and computed from Dithering
C3x
C2x
4bx
4ax
Positions computed by regression (One coefficient
has the wrong sign.)
10
Explanation
ltDMigt
Typical Regression coeficient
ltMi2gt
ltMi2gtlt(Mitd)2gtlt(Mit)2gtltd2gt
Uncorrelated noise reduces coefficients
Need correlated noise to explain data
ltMiMjgtlt(Midi)(Mjtdj)gtltMitMjtgtltdidjgt
11
Electronic noise
If sB sE, electronic and beam noise can be
unfolded (without large subtraction in
quadrature.)
Regression and dithering give different
results Regression is unreliable
Correlations probably invalidate regression
analysis
Dithering implies that both have 1 micron noise
12
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
  BPMs?)