Present:
Chris Allgower, Andy Bacher, Hermann Nann, John Olmsted, Tom Rinckel,
and Ed Stephenson
Pb-GLASS POSITIONS
Chris Allgower reported that he is about half finished with the sketching of the positions of all Pb-glass counters onto large sheets of paper. The front and rear positions of the boundaries between counters are marked on pieces of poster board which are then located with respect to the support plate. These are transferred to a full scale sketch which shows the boundaries between detectors. The actual detector size will be something less than the space shown on the drawing. Accuracy for the front positions is expected to be about 1/8 inch. Information has also been gathered on the vertical position. On beam right, there is some tendency for the top counters to slope toward the target.
RESEARCH EXPERIENCE FOR UNDERGRADUATES
Chris suggested that putting the real detector information into a GEANT array and running simulations of the response would be a good REU summer project, to be done in collaboration with Mark Pickar. Andy has talked to Mark about this, and a writeup is being prepared.
It was discussed, but not decided, whether there would be another project involving management of the data expected to come in during the run.
DATA ANALYSIS
John Olmsted reported on a number of short topics.
He confirms that the shift in the Pb-glass timing peak between the 3He and 4He data is about what is expected from the change in the trigger timing. That change was expected to be 8x4 = 32 ns and found to be 29-30 ns.
Traceback to the target for 4He events shows a clustering similar to that seen for 3He events.
Lowering the Pb-glass energy thresholds to 150 channels from their previous values (320 for left and 470 for right) increases the number of two-gamma events in the most restrictive sample to 18 from 12.
In pb-glass time by energy plots, the timing peak continues to the lower pulse heights used above. A look at the locations of hits that are out of time shows that they appear predominantly in those counters located downstream. These counters are the ones affected by the change in gain from the field of the 6-degree magnet, but their location is also consistent with being at the smallest scattering angle relative to the beam. So it is not clear whether we are dealing with a noise (greater gain) or a rate issue.
Pileup was examined in two different ways. First, hits in the A, B, or C sections of delta-E(1) were used to gate delta-E(1)[D]. There were roughly twice as many hits for harmonic 1 as for harmonic 6, in contrast to the report earlier that looked at "pileup" locations in the scintillator spectra. A check of MWPC multiplicity showed a similar result, almost twice the multiple hits for harmonic 1 beam.
Ed suggested that we try a replay looking at Pb-glass clusters for the earliest time rather than the time for the highest pulse height to see if this improves resolution.
SHIELDING
Tom reported that he and Ted Hall worked on rearranging the plates of shielding steel on beam right. Now there is a 1/4-inch plate as well as the two 1/8-inch plates. Some work is needed to make sure that the detectors can be rolled into position. After that, there should be another test of gain changes with and without the 6-degree magnet.
CALENDAR
On Friday, there will be a workshop in Albuquerque for the theory group working on the calculation of d+d -> alpha+pi0. This will be held in the Boardroom North at the Hyatt Regency Hotel. The program alternates between speakers and discussion periods. The speakers are:
10:00 - 10:45 Ed Stephenson, Experimental Results
10:45 - 11:00 Jerry Miller, Homework Problem
11:30 - 12:00 Antonio Fonseca, dd Wavefunctions
lunch break
2:00 - 2:30 Andreas Nogga, alpha Wavefunctions
3:00 - 3:00 Anders Gardestig, Co-ordinate Space Calculation
This will be followed by a discussion of future plans.
Anyone who is interested and will be at the meeting is invited to attend.
As some people will be staying for the APS meeting immediately afterward, there will be no group meeting on April 22.