PREX Issues
Outline
• New issue: souce systematics and Aug.
07 run.
• Update on old issues.
• Progress at SU
Running With Other Halls
• Helicity-correlations with beam position
much worse with high current operation in
other halls.
• Possible causes:
– Cathode (Hall B and C).
– Cross-talk in the linac (Hall C only)
• Depends on Laser set-up.
• Need realistic test to dermine of PREX
must run alone
10 Day test run in Aug07
• Study cross-talk issues.
• Compton tests (Integration)
• Noise test with LUMI, 18 bet ADC’s, etc.
• Detector (Use Moller spectrometer as test
beam.
Compton-Biggest Issue
• New Hardware
– Green laser
– New photon and electron detectors
• Data analysis
– Rewrite code in C++ style
– Understand systematics
• Integration and Low energy
– Achieve good systematics (<1) with
integration.
Recent Compton Progress
• See later talks
• Observed Compton peak with FADC.
• Work at SU (see below).
Integration test with IR light
• Need to take extended Compton data with
electron analysis, conventional photon
analysis, and integrated Compton analysis
and ahcieve agreement better than 1%.
Plan for 850 MeV Compton
• Assume that some of the time the electron
analysis will work: need to get near
enough beam to get half of spectrum
• Demonstrate linearity of photon detector
response with coincidence data.
• Compute linearity with MC-effect of GDR
neutron production?
• Show that integral and electron agree on
good days.
Warm Septum
• Plan A
– NSF MRI: Request submitted to SU, approved
at Smith (Smith and SU will build the
magnets).
• Plan B
– Build at JLab if proposal not funded.
Open issue: Can the new magnet use the old
Vacuum system?? Other issues? Needs
Focus at JLab.
Need 100 ppm pair noise
• 18 bit ADC’s have arrived.
• Can/should we use Qweak electroncs?
• Do we have difficult ground-loop
problems?
• What is our pedestal noise with the new
setup?
• Critical test: <100 ppm noise with LUMI.
Target
• This spring, a 1/3 thickness Pb target with
diamond cooling will be used in a Hall A
experiment.
• This will test radiation damage of diamond
cooling, radiation, etc.
• Is this a good opportunity for a LUMI test?
• Check cavity-stripline agreement?
Detector
• Only option: thin quartz. Same as Qweak.
• Need to show narrow response to single
electrons: earlier test failed.
• Quartz PMT? More light, less neutrons.
Other Issues (see memo)
• High Field Moller (Compton Cross-check)
–Eugene
• Detector Linearity
• Pole-tip Monte Carlo
• Management of large transverse beam
asymmetry
• Angle measurement
• Low current running issues
Compton analysis at SU
• Fix bugs
• Understand goofy runs
• Study line-shape systematics
Fits to spectra look good
Tails now under control
Difference between poly
and dual exponential
Spike shows up where
Dual exponential
Has discontinuity in
2nd derivative
Noise in FADC
• To integrate, we must add 6x106 samples
without adding too much noise.
• Following data looks promising, but issue
is not trivial.
• Is there more noise running in the hall?
Bin half of one window
Pedestal noise
Is not statistical.
The χ2 gets
Worse the longer
The window
Fanout adds noise
Cavity Monitors: Work in Progress
• Show great promise: Resolution at least
as good as stripline. (Redundancy).
• Gossip: G0 had excellent performance;10
ppm pulse pair width??
• Problems isolated
– Cross talk
– Oscillation
Difference between cavity and
stripline position for one slug
See oscillation
In time (beat
Frequency)
See the same
In the current
Frequency of noise not stable
Plot every fourth point to slow observed frequency and see long times