Minutes : N-star meeting, CEBAF, June 30, 1997
Submitted by Ralph Minehart
I. Commissioning Run:
A. V. Burkert reported on the just completed commissioning run
between June 8 and June 30. Although a lot of effort and time
was expended in gettting a beam, there was initially a good start
with 1.6 GeV, but after a short run of good data
further efforts at 1.6 GeV were not very successful.
We did get reasonably good beam at 4.0 GeV and 2.4 GeV.
Many problems with the drift chambers were gradually cured over
the course of the run and towards the end a lot of data under a
variety of conditions were obtained with good enough acceptance
to make studies of multi-particle final states worthwile.
It is important now to analyze the data, since only by looking
at a variety of exclusive reactions will we learn whether we will
be ready to take data in Sept.
Luminosites up to 10**34 were studied. At the upper limit, Volker
thinks the data are probably analyzable but the beam conditions were
not optimal. Background problems clearly exist, since the target
full/empty ratio for the drift chamber currents is only a factor of
2. Volker also said that he could see tracks in region 1 pointing
to a downstream point. It is possible that some lead shielding was
left
out during the assembly.
The calorimeter provides the most reliable trigger, but it includes
a lot of cosmic ray triggers. The coincidence (inner x outer)
suppresses cosmics but it is not 100% efficient. This combination
with high threshold on both inner and outer gives a pretty clean
electron trigger. A useful trigger for hadrons is [inner(low)xouter(low)],
which has a good track efficiency.
Time-based tracking is important in order to get reasonable resolution
in angles and momenta. Francois Rudot, Richard Cline and Richard Thompson
are working on this. It is also important to get the TOF working and
Latifa
reported that this project was underway, with the first step being
calibration
using laser data. For help in getting information from the electronic
log book,
it was suggested that Elliot Wolin was the person to see.
Stepan Stepanyan will make a list of good runs that should be
of interest to N-star people.
B. Drift chambers:
Mac Mestayer reported on the drift chambers. A number
of broken wires will be removed from two sectors of region 3. Broken
wires in the corresponding sectors of region 2 will be removed if possible.
It may be difficult to get at them, since region 3 sectors will only
be
pulled back about 4 feet. The broken wires in region 1 will be removed.
Mac also reported that most of the electronic problems have been fixed.
A large number of mis-connections were fixed. Discriminator thresholds
were adjusted to reduce random noise in region 3. Efficiency plateau
curves were obtained and used to set operating points. The chambers
are better than 98% efficient per layer. There is some intermittent
noise in the inner layer of region 3 and the inner and outer layers
of region 2. This leads to occasional huge events that are hard on
the data acquisition system. The source of the noise has not yet
been determined.
C. Cerenkov counters:
V. Burkert reported that the installed Cerenkov counter appears
to be working very well, with good efficiency in the fiducial region.
The single photoelectron peaks have been identified, so that it is
possible to determine the number of photo-electrons in a pulse.
Alexis concludes that the counter is operating at close to design
performance, with an average number of photo-electrons between 8 and
10.
Two more Cerenkov counters, sectors 1 and 4, at 9:00 and 3:00 respectively,
are essentially ready to be installed. Sector #5 (the one that exploded),
located at 5:00, is now being prepared and should be ready by mid-August.
Sector 3, at 1:00, will begin mirror installation soon.
Volker expects that five detectors will be installed by Sept.
He also noteed that the chamber gas leakage is at acceptable levels.
In addition to refining the study of the Cerenkov electron efficiency,
a study of the effects of knock-ons is needed.
D. Beam quality:
At 4 GeV the observed beam quality was not as good as it probably could
be.
One problem is that the target is 5 mm below the beam line, so that
it was
necessary to bring the beam in with a vertical slope. This problem
will be
studied to determine whether the beam line should be lowered. Volker
pointed
out that the beam rastering system can be used to compensate for any
additional
displacements that may occur with time. Beam monitoring devices are
being
developed this summer. Low current PPM's now have a high priority and
should be
ready. Problems with the Lambertson magnet ( resulting in interference
between Hall A and B) will be solved by Sept.
II. GSIM
A report on GSIM activities from Maurik Holtrop was read to the group.
K. Joo presented some preliminary results on studies using the new
geometry for the mini-torus developed by Dale Conwell. This has been
checked in, but it is being further revised to try to make GSIM run
faster with it.
III. Graduate student projects:
Four new graduate students who will use the Sept. run for their theses
were identified:
1. Simeon McAleer - FSU - electro-production of lamda's and lamda(1520)'s,
based on proposal E89-043.
2. Min Jeong Kim - Korea - pi+ production in the delta region at low Q2
3. Alan Coleman - W&M - omega production
4. Hovannis Egiyan - Yerevan
Volker agreed to make a list of Ph.D. projects. After review by the
N-star
spokespersons, this list will be put on the web.
IV. Discussion of the fall run: The E1 run is scheduled to begin on
Sept. 11.
It could get shifted some depending on what happens in the commissioning
runs at the end of the summer. We are scheduled to take data at the
energies:
1.6, 2.6, 2.8 and 4.0 GeV. We have previously decided that a minimum
of
4 Cerenkov counters was required for the run. We also are going to
require
a reasonably smooth acceptance in physical variables. The experiments
were
designed with data rates of the order of 1000/s, so that high data
acquisition
rates are needed (either an ATM or fast Ethernet lines). It appears
that we will have to use a liquid target, although our proposals were
generally
developed around gas targets. Getting the beam centered stably on a
small window
in a gas target does not look feasible at this time. It was agreed
that beam
currents of approximately 5 nA stable to 10% were required. Low current
beam
position monitors are essential to monitoring the beam. It is also
hoped
that the Faraday cup will work well. In any case it can be calibrated
against the elastic electron scattering cross section.
V. Miscellaneous:
A. N-star web page. Latifa Elouadhriri is developing an N-star web page.
It should be public in a week or so. It is important for participants
to contribute to the information on this page.
B. Latifa has some students working on the N-star data base,
which will ave cross sections in a multi-dimensional table
(W,Q2,cos theta, phi)
C. Larry Dennis talked about the use of the farm for data analysis
and simulation. He would like people with experience using the farm,
or experience in being unable to use it, to complain to him so that
he can produce a useful web form to submission of jobs.
D. An N-star workshop will be held at GWU at the end of October.
VI. The next meeting will be on Aug. 22, 1997. The chair notes that
there were complaints about lack of cookies and coffee,
and resolves to do something about that for the next meeting.
Attendance:
Volker
Burkert burkert@cebaf.gov
Haluk Denizli
halukd@cebaf.gov
Larry Dennis
larry@fsulcd.physics.fsu.edu
Steve Dytman
dytman+@pitt.edu
Latifa Elouadhriri
latifa@cebaf.gov
Herbert Funsten
funsten@cebaf.gov
Jerry Gilfoyle
gilfoyle@cebaf.gov
Ken Hicks
khicks1@ohiou.edu
Kyungseon Joo
kjoo@cebaf.gov
DongHee Kim
dkim@cebaf.gov
Min Jeong Kim
mkim@cebaf.gov
Mikhail Kossov
kossov@cebaf.gov
Sebastian Kuhn
kuhn@jlab.org
Simeon McAleer
mcaleer@jlab.org
Mac Mestayer
mestayer@cebaf.gov
R. Minehart
minehart@virginia.edu
Jim Mueller
mueller+@pitt.edu
John Price
pricej@jlab.org
Stepan Stepanyan
stepanyan@cebaf.gov