Minutes of the E89044 group meeting, May 22, 1999, at Jefferson Lab

List of participants:

Konrad Aniol
Zhengwei Chai
George Chang
Martin Epstein
Kevin Fissum
Ross Hicks
Jesse Hines
Sabine Jeschonnek
Michael Kuss
Jean-Marc Laget
Laura Marcucci
Pete Markowitz
Itaru Nakagawa
Dimitri Margaziotis
Arun Saha
Silvano Simula
Jeffrey Templon
Eric Voutier
Zilu Zhou

Arun Saha ...

... opened the meeting. He showed the updated run plan and the experiment schedule. Note that the linac energies were modified compared to the draft of the tentative schedule, as requested by E89044. He also addressed a list of items that need long term attention.

• Currently, the momentum resolution of the HRSs is determined by the beam energy spread, the intrinsic resolution is better. The OTR monitor to measure the spread is installed and will be tested. The beam energy spread can be minimized by tuning the phase between the linacs and the injector.
• We still need a reliable method to monitor the target density.
• Collimator thickness
• Complete simulations
• Spectrometer pointing/angle precision
• Other issues related to Emiss resolution
• Spectrometer optics

Jean-Marc Laget ...

... talked about calculations for ³He(e,e'p). Results for one of our settings were already presented in the March experiment group meeting by Gilles Quéméner. Jean-Marc announced he will stay at JLab during the summer (July 10 - September 6). A good time for theorists and experimentalists to discuss with him and calculate around. Particular interest should be on the high E_miss region where the correlations should show up. However, Jeff Templons studies show that the extraction of this cross section is hindered by the radiative tail of the d ground state. He presented all the diagrams which are included into his model. Rescattering is introduced by a scattering series. Because the transition form factor will decrease with increasing momentum transfer he expects to have a small contribution from p-rescattering. However, he pointed out that his calculations are not exact. If we want these Faddeev calculations have to be performed, e.g. from Glöckle. Konrad mentioned that he considers to use a third arm to identify the ³He(e,e'p)np channel. This would veto the ³He(e,e'p)d\gamma contribution from the radiative tail from the ground state. He pointed out that it may also give a handle to unravel rescattering contributions, due to a possible different angular distribution. Discussion remained open.

Martin Epstein ...

... presented the new, fine-tuned runplan.

Zhengwei Chai ...

... reported about optics optimization for E94010 (GDH). With the final data base, the y_tg resolution is sigma<2mm, and for the momentum 2.5·10^-4. Arun Saha emphasized that the momentum resolution is dominated by the beam energy spread. But we don't know at the present time how much the beam energy spread has contributed to the observed E_miss resolution in experiments already completed.

Kevin Fissum ...

... presented the plans for optics at high energy. He introduced the different choices we had:

• Kapton foil stack. Discarded because too low counting rate.
• Waterfall target. Discarded because it needs modification and also introduces overhead due to installation time.
• Liquid Hydrogen target with slit mask.

Kevin summarized that of the three choices the last should be the preferred one. Zilu Zhou proposed that it may be easier to use ep coincidences. The HRSH can be used to define y_tg slices for the HRSE. Additionally, Kevin presented numbers on the behavior of the magnets at high field (large current). Because the quads are current driven they don't exhibit saturation effects. Studies for the dipole, which is "iron" driven, showed that the effective length, which accounts for the Integral(Bdl), is changed by just 400µm, neglegible. From this he proposed two different scenarios for a delta scan, both for fixed beam energy:

1. Changing the spectrometer angle. This will keep the spectrometer field constant, but survey of spectrometer angle and pointing is neccessary.
2. Changing the spectrometer field. This works fine if the optics of the spectrometer scales with field.

George Chang ...

... extended his GEANT simulations studying particle punch-through the collimators. The collimators are quite effective to stop electrons. Protons however, punch through losing about 360MeV. For long target, if they intersect the edge of the collimator they may loose anything between 0 and 360MeV, polluting the high E_miss region of interest. More studies are neccessary.

Michael Kuss ...

... reported for Akio Hotta. Akio studied different methods for a luminosity normalization.

1. magnet type: it would be nice to have a third spectrometer, like A1 at Mainz. We don't have.
2. non magnetic type: third arm detector (e.g. 7/11). A single third arm detector may have background problems.
3. other ways:
   1. using prescaled singles in HRSE
   2. mapping carefully the target density as function of beam current, fan speed and raster size.

It seems we still have no striking idea, but c.1. will link luminosities for fixed HRSE setting, and c.2. may work if the target density does not vary too much with changes in fan speed, beam current, and raster size.

The next meeting will be end of July. Proposed dates are Monday, 26 and Friday, 30. Please send email if you prefer one of the days in particular.