Minutes of the E89044 group meeting, November 12, 1999, at Jefferson Lab


List of participants:
Fatiha Benmokhtar, Algiers
Zhengwei Chai, MIT
George Chang, Maryland
Eugene Choudakov, JLab
Martin Epstein, CalStateLA
Kevin Fissum, Lund
Shalev Gilad, MIT
Doug Higinbotham, MIT
Akio Hotta, UMass
Michael Kuss, JLab
Nilanga Liyanage, JLab
Dimitri Margaziotis, CalStateLA
Jean Mougey, Grenoble
Eli Piasetzki, Tel Aviv
Milan Potokar, Ljubljana
Marat Rvachev, MIT
Arun Saha, JLab
Simon Sirca, Ljubljana
Riad Suleiman, MIT
Paul Ulmer, ODU

Arun ...
... opened the meeting. He showed the final experimental schedule as published November 5. There are minor changes compared to the tentative schedule published a month before. He also showed the updated kinematics table. The high pmiss and Emiss points still have to be added. He mentioned the problem of the post which have to be placed to stabilize the slits in the scattering chamber. They will be placed at around 110o on both sides. Shalev took advantage to mention that during E89044 there will be another experiment running parasiticly. The 7/11 third arm detector will be placed at about 120o on the HRSH side to detect a third particle.

Marat ...
... spoke about the absolute normalization and luminosity monitoring scheme he and Konrad Aniol are working on. The general procedure is described in Konrad's write-up. There were questions about how the single rates are really a reliable luminosity monitor. It was mentioned that the "real" singles rate can be reconstructed from the "latched trigger pattern" in the data stream. Marty mentioned he learned from Meme's report that the dead time correction works even if, e.g., the coincidences are scaled. Shalev mentioned to be careful not to run the monitor in a kinematics were the yield changes strongly with a particular spectrometer parameter. A small change of this parameter may fake a change in luminosity. Marat and Doug will be responsible for quality control of the normalization runs through the experiment.

Paul ...
... spoke about the status of MCEEP. He said that several bugs were found in version 3.0, they will be corrected in 3.1 to be issued soon. The solid angle for a long target was not taken into account correctly. Also, the smeering to simulate the finite resolution of the detector systems was not working correctly. MCEEP treats the energy loss of the particles in the gas correctly. It uses a constant thickness for the target cell wall, thus it neglects the change due to non vertical intersection. It has exteral and internal Bremsstrahlung. For internal it uses Borie/Drechsel in peaking approximation. It also has second order corrections for multi photon emission. Here is still some discussion about the correct method to use. Both give slightly different results, but the uncertaincy is in the few % range. If the user does not trust in this feature there is a flag to turn it off. For tracing the particle through the spectrometer it has John Lerose's functions for backward and forward tracing. The backward function in 3.1 will be modified due to a change in effective field length. Also the tuna can incorporated by Marat and Riad will be in the next release. There was an inconsistency in the integrated cross section weighting for two different outputs, it is fixed too.

Arun ...
... spoke about the beamline related issues. He reported that the current calibration is a well established procedure. The hall A beamline current cavities are well calibrated to the OLO2 monitor in the injector. The VtoF scalers again are calibrated to the cavities. They are linear down to the some 100nA region.
For the energy, the Bdl measured with the 9th ARC dipole is constant to 10-5. This information will be fed into the data stream. Shalev suggested to have some write-up for the shifts to tell people what to check. There was a discussion about what should be monitored by the shift and what written automatically into the halog. Michael agreed to distribute a "trial run sheet".

Michael ...
... reported on the commissioning run plan. However, first he reported that the 3He is on it's way from MIT-Bates and is expected in any time.
The commissioning run period actually consists of four independent topics. The beam energy will be 0.845GeV.
  1. Nilanga's optics studies with 12C at forward angles (16.54o)
  2. the actual commissioning studying the target density under different beam and target conditions
  3. elastic runs at different Q2 for absolute normalization
  4. data taking of kinematics #17 and #27 which were actually intended to run at 1.003GeV
It was recommended to use the HRSH instead for the commissioning. Thus HRSE can remain at 16.54o for the first Q2 point. Also, it should start with the highest target density possible (970mg/cm2) and also commission at 1/2 and 1/4 density. The commissioning run plan reflects these recommedations.

Dimitri ...
... spoke about the shift schedule. Seems December is pretty good filled, though there are still some shifts left. Check the web page for sign-up. For target operator training, new operators will be trained as usually, old operators will get their 3He upgrade during their first shift with the Helium target. One issue is the uncertaincy when the commissioning will actually run. It will be difficult to get external shift people on short notice, thus it may have to be manned with JLab locals.

Kevin ...
... worked on the kinematics matching. He pointed out that it is not possible to simultaneously match Emiss, pmiss, omega and q exactly, there has always to be kind of a balance to get the most information. One important topics is how to choose the high Emiss settings. Though one dimensional plots seems to show a good overlap of Emiss and pmiss two-dimensional plots unravel that it is not the case for the high Emiss. However, due to the spectrometer acceptances there is an overlap with settings taken at other adjacent pmiss. Also, Kevin proposed to change the HRSH momentum by about 40MeV/c for all settings. The current run plan is for central kinematics for the two-body state, this modification moves the latter of the center and allows for higher Emiss.