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:
- maximum field cannot exceed 4 GeV (in HRSE).
- 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:
- a third point relies strongly on the beam energies available and may
not be in the middle of the low and high epsilon.
- 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.
- 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:
- spectrometer precision and pointing ("Do we get the precision we
need?")
Nilanga, Arun
- collimator thickness for continuum measurement ("At which Emiss for
(nnp) do we see the (pd) channel punch-through?")
George
- 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:
- read the "Cryogenic Target Control System User Manual". It is on the
target web page, accessible from our web page.
- 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.
- Sit a few shifts (two is the average) during a regular experiment.
Another certified operator will be on shift too.
- 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:
- How reliable are the Cernox? Those installed showed radiation aging.
- Is the pressure at the gas panel the same as in the loop? The fan may
cause a pressure gradient.
- 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:
- 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.
- 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.
- 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:
- for the Mainz He(e,e'p) the strength above 30MeV was essentially
radiative tail.
- 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.
- 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.