Minutes of the E89044 group meeting, March 26, 1999, at Jefferson Lab


List of participants:
Akio Hotta
Bogdan Wojtsekhowski
George Chang
Martin Epstein
Kevin Fissum
Xiaodong Jiang
Jim Kelly
Konrad Aniol
Michael Kuss
Marat Rvachev
Nilanga Liyanage
Gilles Quemener
Sabine Jeschonnek
Arun Saha
Shalev Gilad
Jeff Templon
Eric Voutier
Zhengwei Chai

Arun Saha ...
... presented the "prospective final" experiment schedule for the second half of 1999. Modification to the "tentative schedule" is that E89044 is swapped with E93049 (pol. transfer in 4He(e,e'p)). Thus, E89044 will start on Dec 11 and run till mid March 2000. The "prospective tentative" schedule for the first half of 2000 shows an accelerator downtime in January. The old schedule was motivated by the fact that Hall C would run 3He till December which was assumed to be needed by E89044. Now there is another source ("Barry Berman Helium") which together with the "Gerry Peterson Helium" is a sufficient amount.
The schedule in detail is for E89044 to run from Dec. 11 to Dec. 23 and then to start again at the end of January, 2000 and finish around mid March.

Marty Epstein ...
... presented the updated run schedule. The main change is that instead of running at \vec{q} of 1 and/or 2 GeV/c we will run at 1.5 GeV/c in perpendicular kinematics. The parallel kinematics that are planned are very similar to what had been proposed before. In addition there will be time set aside for data taking in the large Emiss region. As the discussion showed those settings are an outline, they will have to be modified anyway. Most likely the maximum beam energy we will get is about 4.5 GeV. The other requested energies seem to be uncertain and have to be adjusted/negotiated due to the needs of the other halls. In the discussion two more things were mentioned:
  1. maximum field cannot exceed 4 GeV (in HRSE).
  2. minimum field so far used was 400MeV (E89033 "Oxygen" and E91026 "deuteron"). At that time field control was difficult because the "low field" probe didn't find a resonance. It was mentioned that now the "high field" probe can be used alone. It was asked what the lowest possible field is. Someone mentioned that if one leaves the range where people have measured previously one may not know that the "is-field" is actually the "set-field".
Shalev renewed the discussion about a third epsilon point which apparently wasn't on the run plan presented. The following things were discussed:
  1. a third point relies strongly on the beam energies available and may not be in the middle of the low and high epsilon.
  2. a third point does not need to be in the middle, it simply needs to be a measurement which is independent from the previous, e.g. moving spectrometer and field and try to reproduce.
  3. there appears to be a bug in the code which optimizes the times to be spent for the different settings (flux was not squared).
To 3 and 4 of the beam time request (large Emiss):
Jeff et al. will spend time to work that out. He also mentioned that from his simulation q=450MeV/c should be favored over 300MeV/c (less radiation background). Marty also proposed to cover the largest Emiss possible. Asked how far we can go. See Jeff's talk in the afternoon.

Marty Epstein ...
... presented a list of problems that have to be solved. During the discussion other topics were mentioned, and people volunteered/agreed to think about and give a presentation in the next meeting. Those were:
  1. spectrometer precision and pointing ("Do we get the precision we need?")
    Nilanga, Arun
  2. collimator thickness for continuum measurement ("At which Emiss for (nnp) do we see the (pd) channel punch-through?")
    George
  3. complete simulation including spectrometer optics. We still have no general simulation program in hall A. Xiaodong is working on a simulation for E94010 ("GDH") based on SNAKE. Jeff mentioned that the "Hall A software group" agreed that MCEEP should be favored. Following people have volunteered:
    MCEEP:
    (radiation tail has to be incorporated)
    Kevin, Marat, Eric, Gilles
    AEEXB:
    (radiation tail is in)
    Jeff et al.
    Hall C simulation:
    (Jeff mentioned that hall C has a very fancy radiation code)
    Michael
  • Emiss resolution achieved with thick target (replay of data):
    Jeff, Michael
  • review of calibration/normalization, ep scattering, elastics:
    (What is the status of H(e,e'p) and 3He(e,e'p)? What do we need? Hydrogen foil target or extended target? There should be a possibility to fill the Helium cell with Hydrogen [gaspanel-->Michael].)
    Marty, Shalev, Michael
  • preparation of kumacs: has low priority, should be done by the students with help of the post-docs.
  • kinematics optimizer:
    Arun, Grenoble, Marty
  • optics studies: (see also Nilangas talk in the afternoon)
    Nilanga, Marat
  • luminosity monitoring:
    Konrad, Akio
    • It was also decided that the next meetings should be:
    Saturday, April 24
    Saturday, May 22 (collaboration meeting is 23-25)

    List of students:
    Marat Rhachev MIT Bertozzi
    Volker Kuhlmann UGa Templon
    Fatiha Benmokhtar Algiers Amroun

    Arun initiated that everyone becomes cryo target operator. Procedure is:
    1. read the "Cryogenic Target Control System User Manual". It is on the target web page, accessible from our web page.
    2. ask one of the experts (JP, Kathy, Gary and Michael) to give a training (takes about 3h). This is possible only if the target is at LH2 and there is no beam on the target, i.e. during short maintenance periods. Michael will make a table of those periods for 1999 and put it on the web page.
    3. Sit a few shifts (two is the average) during a regular experiment. Another certified operator will be on shift too.
    4. If you feel experienced and your trainer feels comfortable enough JP will certify you.

    Michael ...
    ... presented some thought on target conditions. The Cernox temperature and the pressure transducers available are good enough to control the density within a few 0.1%. The discussion raised the following questions:
    1. How reliable are the Cernox? Those installed showed radiation aging.
    2. Is the pressure at the gas panel the same as in the loop? The fan may cause a pressure gradient.
    3. How do we know from the information measured elsewhere the conditions in beam?
    The discussion about luminosity monitoring came up again.

    Nilanga ...
    ... presented an overview about previous optics studies. He pointed out:
    1. previous studies with the waterfall target gave 2.5-4*10-4 for momentum resolution. We should not expect to be better with an extended target.
    2. At 3.7GeV/c (current run plan) we are deep into saturation. Optics studies moving the elastic line over the focal plane should be performed at constant field (changing beam energy or scattering angle), which adds complications.
    3. VCS used the Hydrogen target for dp and angle studies (because of the cross section) and the dummy targets + carbon (7 foils in total) for y_tg studies.
      Arun mentioned there is now a Kapton foil on the solid target ladder. We should test this foil for high beam currents, and if successful, build a foil stack to be mounted on the target ladder. It should be checked when the tests are possible (the next "facility developement time" is May 8-10). The target stack has to be ready end of May to be installed while the fan of loop 2 will be replaced (Michael was volunteered).
    There was also some discussion about using commissioning time to do optics studies. The only time available at resonable beam energy is in November 99.

    Jeff ...
    ... presented his simulation for high Emiss. He pointed out that:
    1. for the Mainz He(e,e'p) the strength above 30MeV was essentially radiative tail.
    2. due to the uncertaincy of a radiative tail correction (20%) one should measure in a region were the expected strength outruns the radiative tail contribution.
    3. his simulations show that the higher the momentum transfer the larger the range of Emiss accessible.

    Gilles ...
    ... investigated the possibility to study the proton recoil polarization pn parasitically. He had predictions of Laget and compared that with the statistical error he can achieve. Results were that only in one kinematics the error would be less than the predicted value. Additionally, to also minimize the systematic error extended studies would be neccessary. Conclusion is that it is not worth trying.
    Second part showed updated simulations of the precision we can achieve for the three response functions. He assumed systematic errors between 2 and 5%. An interesting result was that the overall precision does not change so much except for RL. Thus, we are not totally killed if we do not achieve the overall goal, as some of us believed.

    There was a discussion whether or not it makes sense to spend a lot of beam time on pmiss=0.55GeV/c, because the error for RL will be about 90% (essentially an upper limit). Arun pointed out that even that already would constrain theory, and we still lack of predicitions beyond PWIA. Marty also supported Arun's remarks. Thus, we will proceed with the measurement at pmiss=0.55 GeV/c.