Notes from Meeting Mar 13, 2009

• HAMC Simulation Comparisons

• Discussion about Dustin's HAPLOG 1557 -- comparing x,y spectra of HAMC with real data.
• HAMC comparison with HAPPEX-II hydrogen 2005 test data at ~3.18GeV and 6 degree scattering looks good for the dispersive (x) direction, but is significantly different for the transverse(y) direction. Should investigate first order transport matrix elements between HAMC and real data to see if any significant differences exist.
• For the Pb comparisons (2005 test data at 1.1GeV and 6 degree scattering), the x again is not too bad, but the y comparisons are "un-impressive and under-developed". Someone noted that it is ~embarrassing that we cannot reproduce the y spectra for Pb and furthermore that getting the y distributions right is important for PREx (unlike many or all previous hall A experiments).
• Next steps for improving the simulations is to incorporate Guido's forward transport matrix into HAMC and see if this improves the comparisons.

• Forward Matrix Studies

• Discussion about Guido's HAPLOG 1555 -- Optics target calibration for 2005 test data at 3.18GeV and 6 deg.
• After calibration of the forward matrix using run 3050, delta-x distributions (difference between focal-plane x from VDC data and new forward matrix) gives 1.6 mm sigma using the downstream carbon foil and ~2.5mm sigma using the center foil (both of these results use the full angular acceptance of HRS).
• Question for Guido. How did the delta-y distributions look?
• Kent and others requested that Guido give Dustin and Bob his forward matrix for the 3.18GeV run (to incorporate into HAMC) and then work on calibrating the forward matrix using the optics run 3133 at 1.1GeV (useful for Pb comparisons). Once this is complete, again send it to Dustin and Bob for using in HAMC.

• ADC Testing

• Discussed Luis's latest ADC tests of non-linearity in HAPLOG 1553 and 1550.
• Differences between the 16bit and 18bit ADC non-linearities discussed during the last meeting were found to be due to a pedestal mis-calibration. After addressing this, both the 16 and 18bit tests gave consistent results with respect to the (beta * N0) term and the Integration Time (IT) scans.
• Luis will continue to map-out the ideal settings (PMT HV, ADC gain, IT windows) for optimal linearity under various input light level conditions.
• He noted that the linearity is great for light levels at or below 2nA, and that for input currents above 10nA we need to carefully study the ideal settings for each PMT/ADC combination.

• FADC Compton Asymmetries during d2n Runs

• Discussed Diana's latest HAPLOGs 1558, 1552, and 1551.
• From 1551 -- which looked at 7 different runs during 3 (1/2)-wave plate flips, consistent asymmetries were found between each of the runs/wave plate flips as well as between the two different accumulators analyzed--accum 1 (ALL) integrated all charge while accum 2 (WIN) integrated between a high and low threshold.
• Also noted here was the proper use of the CML-bit -- which reduced the pedestal width by a factor of 7 to 10 resulting in the much smaller error bars achieved for the asymmetries.:)
• Entry 1558 examined the correlation between the Moeller measurements and Compton asymmetries which looked very linear with the exception of one run 60527.

• Compton Electron Detector

• This past week, new shielding was installed in the e-detector; 100um Al was replaced with 500um Cu (this should cut down on dark current). Alexandre noted that the e-detector u-strips looked fine (no visible beam damage to hardware).
• Alexandre noted that he has taken a few runs and will examine data in detail. For now, he noted that he adjusted the threshold but still doesn't see good tracks or any correlation between Laser on/off, but does see correlation with beam on/off and that the detector rates track linearly with beam current.
• Next steps are to use a source to help troubleshoot this after the d2n run ends--Monday (Mar 16, 2009) morning.

• PREx Collimator Be Plugs

• Discussion about Bob's HAPLOG 1546 and 1545.
• There was a mistake made in the calculation of the thickness of the Beryllium plugs needed to give the desired momentum shift in the focal plane (for monitoring the transverse beam polarization during PREx with satellite detectors). The result is that very thick Be plugs (~1cm) are needed which result in significant multiple scattering effects -- which make having two plugs in one collimator not possible, thus the plan is to have only one plug for each collimator. Details are still being worked out.

• Hall A Moeller Upgrade

• During Moeller meeting last week it was agreed that the upgrade would proceed this summer (as planned).
• Javier will lead/oversee the effort. Since Sasha is leaving soon and Eugene is very busy with Hall D, Arun Saha has been asked by Kees to be involved in the upgrade.

• Green Cavity Development at Jlab (Abdurahim reporting)

• Mirrors: Have learned which chemicals work best for cleaning mirrors. Also realized that mirrors are being scratched when cleaning them. Will send unopened mirrors back to vendor for cleaning.
• Past achievement: Able to lock 240ppm (lowest finesse) mirrors without cleaning them using the fiber-laser to give ~1kW of cavity power. Bob comments that perhaps we should simply pick the best mirrors that have been proven to work and push forward with the cavity construction.
• Abdurahim is currently working on measuring the laser polarization in the cavity.
• He also reported that work on the feedback/locking electronics is slow-going since the lead engineer, Dan Sexton, can only dedicate very little of his time to this task.
• Gordon gives Abdurahim some technical advice on the final step in cleaning high-finesse cavity mirrors..."Drag and Drop" and "Single Swipe" techniques using methanol and Kodak Lens paper...

• Parity Collab Meeting Scheduled for Apr 17 and 18, Agenda TBA



Comments to: Dustin McNulty