Cooler-CSB Group Meeting Minutes

April 29, 2002 - (EJS)

Present: Chris Allgower, Andy Bacher, Chris Lavelle, Hermann Nann, John Olmsted, Tom Rinckel, and Ed Stephenson

NSF SITE VISIT

The NSF will be here May 20 for a site visit to evaluate IUCF after the first year of physics under the new 3-year grant. Ed will give a 20-minute presentation covering mostly progress on CSB.

There will be a poster session in the afternoon. The posters from this group will be:

  1. [Chris Allgower] A summary of the experimental design and the performance of the detectors.
  2. [John Olmsted] A summary of the experience to date with commissioning, with particular emphasis on the software tools to identify good events and how well the tools work.
  3. [prepared by Chirs Lavelle, with possible presentation by Paul Pancella as Chris will be out of town] A summary of the luminosity system with performance demonstrations.

Pb-GLASS TIME SPECTRA

John Olmsted reported on further investigation of the correction of the Pb-glass time for changes to the trigger timing with changing alpha particle energy. Using the 3-He data for reference, he found that the best slope, as defined by the most narrow time peak, was 0.78. Some single spectra suggested larger values. This produced time peak FWHM of 2.6 and 3.0 ns on the left and right sides respectively. This study used the earliest valid time within each cluster, rather than the time of the highest energy deposition.

OTHER ANALYSIS NOTES

John also reported that a change of the missing mass reconstruction algorithm from producing energy vs. TOF to momentum vs. TOF seemed to produce a slightly better fit.

Some improvements in data readout were made to the display program. A problem with energy values appearing instead of time was corrected.

PERSONNEL FOR THE UPCOMING RUN

Tom Rinckel will be on vacation from May 5 through 19 (overlapping the run). Jack Doskow will be here.

Paul Pancella arrives the weekend of the first run, and will be in the lab on May 13.

Jack Rapaport arrives Thursday, May 9, and will leave again on Tuesday, May 14.

The was no suggestion of a change to the basic assignment of people to shifts. We should plan on being available starting Wednesday, May 8 for some evening or overnight duty. For the long runs, visitors will help to give local people breaks.

Pb-GLASS SHIELDING

The most recent tests with the steel shielding for the Pb-glass showed that there are only small gain shifts on beam right. The ones on beam left are larger, but manageable. We need to repeat these tests.

MISSING MASS RECONSTRUCTION

Ed reported on some investigations of missing mass reconstruction. The original missing mass resolution for 3-He applied to the data taken with the 0.95-degree cone. That gives a FWHM of about 0.28 MeV. If you look at the 1.55-degree data, this width increases to 0.8 MeV.

The problem is more apparent in a plot that shows missing mass as a function of time-of-flight. There is an intense band in this plot that makes a figure-8 shape about the line at 135 MeV. This comes about because of dispersion in the 6-degree magnet. This effect shifts the high energy 3-He events to the right and the low energy to the left relative to the channel centerline. Thus the transverse momenta added to the longitudinal component are not correct. To compensate for this, a shift was introduced that introduces a slope of 0.058 (X channels)/(TOF channels) centered in both distributions. This correction eliminates the figure-8 and reduces the 1.55-degree FWHM to 0.5 MeV.

Ed also looked at the effects of offset errors in the z-component of momentum. These take the ridge at 135 MeV in the plot of missing mass by TOF and tilt it, so that the projection of the rigde on the missing mass axis is larger. Ed looked for evidence in the alpha data of a tilted ridge, and found none. Nevertheless, the missing mass reconstruction is very sensitive to such errors, and the values of the parameters from the 3-He run may not give the best result, thus obscuring the alpha+pi0 peak in online analysis.

DISCUSSION OF THE RUN OBJECTIVES

The purpose of the development time during the week of May 6 is to find the Cooler setup that produces the best (2-3 mA) beam for this experiment. Crucial issues will be:

  1. finding the intensity limits in the Cooler.
  2. exploring whether harmonic = 1 can be used to spread the beam in time by reducing the RF power level without losing cooling. Monitors of pileup include multiple hit spectra for the MWPCs and tests that show multiple delta-E hits.
  3. mapping the lifetime as T_WIDE is scanned across the aperture. This will tell us if the jet target is in the middle of the Cooler acceptance.

The main issue will be to continue to search for a better reconciliation between the luminosities measured with the silicon system and the scintillator system (25 - 44 degree detectors). The plans include:

  1. raising and lowering the beam with T_LIFT and look for changes to the silicon luminosity measurement. This checks for shadowing of the silicon detector.
  2. checking coincidence timing for all systems, with particular attention to the TFA for the silicon detector.
  3. adding 1/4-inch delta-E paddles in front of the 25-degree detectors to make sure that the forward deuteron flux is not contaminated with protons.
  4. checking the silicon system by removing the copper absorbers. A passing scintillator may be added at the end of the stack. We want to resude reaction losses, but not pick up extraneous protons from breakup. Such protons will initially have the same velocity (and thus dE/dx) as beam deuterons.

We can add Cooler RF timing to see whether it helps to sort out spurious events.

As the rate increases, we need a monitor of PMT gain sag. Ed will look into spectra showing pulse height as a function of flattop clock. We may also need to patch signals upstairs for inspection. There was some discussion, but no conclusion, about whether thick shielding could be added to block some of the unwanted particle flux.

It was decided to swap the TFC for the channel, but to make sure that the old system was calibrated against a pulser before removing it. Then the gain of the new TFC could be adjusted so that the pulser gives the same result. We should go back to the original cable used with the 3-He run.

We also discussed looking at the timing down the channel for particle groups other than 4-He. This might force us to remove one of the veto detectors from the trigger.