Present: Andy Bacher, Anders Gardestig, Chris Lavelle, Hermann Nann, John Olmsted, Tom Rinckel, and Ed Stephenson
Shop work
An actual silicon detector has not been tried in the new mount. The shop is working on the dog-leg vaccuum pipe. The parts for the Pb-glass mounts are probably finished and need to be checked. The parts came in from the outside shop for the magnet field clamp. These were assembled and everything looked OK. So Tom had the assembly painted. The plate for the snout came in. It needs to have its beam exit hole cut.
This week we need to come to final agreement on the scintillators that need to be made.
Tomorrow we start to assemble the target box in place. This, after alignment, will locate the mating flange to the 6-degree magnet. That will be tack welded in place, then made leaktight in the shop.
Detectors and stuff
The replacement controller for the high voltage supply works well. There are a few non-functioning channels.
All of the Pb-glass detectors have been checked for light leaks. All have been wrapped with mu-metal. This check should be done again as the Pb-glass is assembled.
Schedule
The schedule between Thanksgiving and Christmas will contain proton running. It will start with the run for the Michigan group that was postponed in September. Given startup time, this will take about 2 weeks. The remaining time will go to CSB to run the p+d -> 3He+pi0 checkout of the Pb-glass. After the Christmas break, we will change to the deuteron vanes and begin deuteron beam running. Concern was expressed that this offered no contingency in case anything happened to the checks with the proton beam. For the "end-game" in which we are presently caught, the only option is to slip the schedule until each objective is met. There is no future time to which you could return later. For CSB, this would mean picking up again in January if the December run is not complete.
Luminosity run
Two options have been considered for doing the calibration of the luminosity detectors. Both would involve a cross-calibration with HD gas between d+d and d+p elastic scattering. They are:
E-mail messages were exchanged with Antonio Fonseca about the angle range he would like for a set of d+d elastic scattering data. His choice is to go for wide angles that would stretch to 90 degrees in the center of mass, provided that there is no deep diffraction minima that would be hard to calculate. We don't know how to anticipate what we will see, so we choose the large angle scheme. This is best met with the PINTEX detectors in their present place, augmented by the silicon detectors to provide coincidence measurements to constrain the elastic scattering locus in the midst of many breakup protons. For the luminosity system in particular, this does not argue for the small angle capability.
The second question involved how steeply the cross section varies across the detector acceptance. We can anticipate this only for d+p scattering. The closest data set covering the right angle range is for 140 MeV nucleons (or 280 MeV deuterons). We will run 231 MeV deuterons. For Paul's elastic scattering angles of 3.8 to 4.7 degrees, these would be 11.7 to 14.5 degrees in the center of mass. At 140 MeV, this angle region is just on the outer edge of the Coulomb-nuclear interference region where the Coulomb is getting to be very small. The cross section here tends to be rather flat with angle and thus is not particularly sensitive to small changes in beam position or direction. This argues that we do not really need information on the slope of the cross section at the luminosity monitor.
Both of these considerations argue for doing the cross calibration in the T-region with the luminosity detectors. HD molecular gas has been ordered. We would use a local mix of H2 and D2 for tuneup.
One possibility is to divide the front scintillator (two will be needed for particle identification) in theta. Any change in the relative rates would signal a change in the beam.
Theory consideration of a new channel
Anders suggested that we might want to be aware that the system will also accept events from the d+d -> 4He+pi0+gamma reaction. This is isospin allowed and enhanced by about two orders of magnitude, but is also suppressed by a factor of about alpha because of the additional gamma. These two factors tend to cancel, giving the possibility to see this channel as though it is part of the 4He+gamma+gamma background. (The extra gamma would likely be at too low an energy to trigger the Pb-glass.) Spin and parity conservation require that there is an additional factor of (k/M)**2 because P-waves are the lowest allowed pion wave. This tends to suppress this process further. The phase space would only permit this channel to fall between the pion and the 138-MeV endpoint in missing mass. The phase space shape is not known.
Experimentally this is likely to become confused with the 4He+gamma +gamma channel, so it would be a distortion to the phase space shape of the 4He+gamma+gamma channel in the region where the phase space is not modulated by the channel acceptance.
It was agreed that Anders would communicate this to the rest of the theory group. It might be possible that power counting could help to make a better estimate of the rough size of the cross section.
Future meeting schedule
Running on STAR at Brookhaven will take Chris Allgower and Ed Stephenson away for a number of future meetings. Various possibilities were discussed. It was decided for the short term to meet again next Monday.
Future short term tasks include:
Next week is the fall meeting of the DNP in Hawaii. Ed Stephenson will present a 15-minute talk (the Maui meeting standard contributed talk length) on the plans for CSB.