Minutes of the E89044 group meeting, October 15, 1999, at Jefferson Lab


List of participants:
Zhengwei Chai
George Chang
Martin Epstein
Shalev Gilad
Akio Hotta
Michael Kuss
Nilanga Liyanage
Dimitri Margaziotis
Marat Rvachev
Arun Saha
Riad Suleiman
Larry Weinstein
Eric Voutier

The next meeting will be held Friday, November 12, 1999, at Jefferson Lab.

Arun ...
... opened the meeting. He reminded us that the goal of the meeting was to finalize the run plan, in all details. Such a plan is also requested by the lab, as well as preparing a conduct of operations (COO), a radiation safety assessment document (RSAD) and an experimental safety assessment document (ESAD). He already worked on the COO and is now on the RSAD. The RSAD may be a problem because running with full target density we may exceed the lab limit, which would trigger a lab review that may request shieldings. But we would not use 100µA and full target density.
In an email to Ed Folts he summarized the preparations that have to be done in the hall. Main tasks are the Helium target and the LVDT system for spectrometer pointing. He reported that we also have to communicate to Ed the angle ranges for both spectrometers as soon as possible. Eventually the floor space has to be cleared.
For the experiment schedule, there is still no final schedule for Jan-Jun 2000, and even the December schedule may change. So far there are only rumors, but changes may be:
  • December 8-10:
    Hall B will run 2-pass, hall A 1-pass.
  • December 17-23:
    Hall B may ask for 2GeV, which is also on our run plan. Thus, CEBA has to be tuned for 0.4GeV per pass, instead of 1GeV. Arun said that such a low energy was never done before, so there are some doubts in MCC that this will be straightforward. But nominally, we will get the energy we asked for, so there is nothing we can do about that.
  • February and March:
    Experiment e1 and g3 may trade places. Under those circumstances, also the CEBA energies have to be modified, and we have to redesign our energies and planned settings. The strongest impact might be that we would not get 4.795GeV in February [1]. We have to resolve this issue soon, i.e. the lab management has to come to a decision, in order to finalize the run plan.
  • We plan to have a third epsilon point, a detailed discussion is below.


Nilanga ...
... spoke about the status of the spectrometer optics and the data still to be taken, please check his transparancies. Due to the problems with the polarized gun he could take most of the optics data we need, mainly to determine matrices for the HRSE at 4.0GeV and the HRSH at 2.8GeV. The analysis of these data is in progress, he promised to have them finished till December. The main issues remaining are the spectrometer constants, which are known only to 3·10-3. He plans to take the neccessary data during the cryotarget commissioning. The full procedure includes a survey of the spectrometers, beam energy measurements and 12C(e,e) elastic scattering. Thus, he prefers a low beam energy, which is now also favored for the commissioning.

Marty ...
... spoke for Konrad about the absolute cross section normalization and luminosity monitoring. Please check Konrad's document for detailed information. Briefly, the singles rate in the electron arm will be used as a relative luminosity monitor. This singles rate will be linked to the elastic 3He(e,e) cross section. Finally, because this cross section is not well known over the entire Q2 range utilized, these measurements have to linked to the cross section at the lowest Q2 which is known to about 0.9%. There was agreement that this scheme is the best scheme we have. Shalev questioned the error estimate which gave about 2%.

Akio ...
... spoke about a third arm detector as a luminosity monitor. Details you find in his and Ross Hicks Luminosity Monitor for E89-044 report. The new design does not consist of a single detector but of three scintillators (thin and small size) oriented on an axis pointing to the target at an angle of 120o. Well aligned, only events originating from the center of the target will trigger triple coincidences. Simulations show that accidental triple coincidences due to background radiation can be suppressed by using the fast timing gate and fast electronics. This telescope has the advantage that it is able to monitor the relative luminosity change in short time intervalls (one to a few minutes), assuming reasonable counting rates. The absolute accuracy has to be checked using the spectrometers (measuring the 3He elastic cross section). An absolute accuracy better than 5% would require further tests. In practice, some effort would be needed to tune the telescope in order to achieve optimum performance. It was also doubted that the device will be much better than 5%.

Riad ...
... talked about scattering on Hydrogen. Having the Hydrogen filled into the Helium cell one can check the capability of the simulation program to model the spectrometer acceptances, because the elastic Hydrogen cross section is well known. This method was already applied in E91026 (deuteron). Because the change to Hydrogen takes about two shifts, all Hydrogen measurements should be done in one block, prefereably at the end of the beam time, when we stay at 1.2GeV for the entire March. Both coincidence and single-arm data should be taken. The proton kinematics are adjusted to the same scattering angle as for the absolute normalization 3He(e,e) data. Riad promised to distribute a table of the settings [2].

Michael ...
... reported on the cryo target status. What he had to report about the 3He shipping became obsolete in the afternoon when Jim Bennett (local DOE office) brought news. He said that DOE Savannah River permitted the shipping of the 3He used by Gerry Peterson at Bates. A fax is being sent to Bates to authorize the shipping.
The work on the controls is going on. The temperature sensors are working and can be controlled by the GUI. Modifications for the pressure transducers and the compressor controls are going on. He does not expect problems because the hardware that will be used worked when tested, and the software could read those channels.
Michael presented also a brief draft for the target commissioning. The performance of the fans and the overall gas panel can be tested after the first cool down. For the test of the target heating effects, he proposes to use a beam energy of 0.8GeV instead of 4GeV from the run plan, and to study elastic scattering instead of quasi-elastic. At an angle of 40o he expect about 500Hz from the elastic scattering, at a beam current of 100µA. If the break-up drives the rate above 2kHz, the rate can be easily adjusted going backward with the spectrometer. This setting then will be kept unchanged during the commissioning. In addition to the heating studies he plans to study the gas density as function of time when the target is instable, i.e. if the beam is switched of and on. Comments were that also the behaviour of the target at different densities should be studied, and also the temperature sensors have to be studied. Michael reported that the data logger works, but the data logger GUI to visualize the data not. He will work on it.

Larry ...
... convinced us that a third epsilon point is highly recommended when performing Rosenbluth separations. It is a good tool to understand systematic errors. Thus, it is useful if the data are dominated by the systematic error. It was concluded that we should measure at a third epsilon for the data points with pmiss=0MeV/c and 150MeV/c, and we should split the high epsilon points at 300MeV/c into two separate runs.

Eric ...
... proposed some modifications to the run plan. Here are his transparancies: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. The modifications were mainly triggered by the fact that the HRSH momentum for setting #23 is below 300MeV/c, which he considered to avoid. But in the discussion it was agreed that this low momentum does not establish a problem, so we should not change the plan. He also proposed how the given beam time should be shared among the various settings, in order to get the most information out of the data. Essentially, his presentation led over into a discussion during which a table of settings was decided. This table will be checked during this week and will be posted in the next.

Dimitri ...
... sent out an email to the halla_coll mailing list asking for participation in E89044. You can sign up for shifts by going to the web page he prepared.

Marty ... ... reported on the status of the simulations. He summarized that we have now five separate groups that are or were working on simulations.
  • Jeff Templon et al.: radiation tail using AEEXB
  • George Chang: Emiss resolution using GEANT
  • Marat Rvachev: Emiss resolution using MCEEP
  • Grenoble group: kinematics optimization using MCEEP
  • Kevin Fissum: omega-q matching using MCEEP

Marat ...
... reported on his simulations using MCEEP. Here are his transparancies: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13. The first goal was to check George's results. Those simulations predict that it will be difficult to separate the deuteron ground state from the break-up channels using the full target density. MCEEP, like GEANT, includes ionization loss in the target and external Bremsstrahlung, but additionally also internal Bremsstrahlung. For particle tracing MCEEP uses John LeRose's transfer coefficients. Marat and Riad added the tuna can geometry to MCEEP. For the beam energy uncertaincy Marat uses a gaussian distribution with a FVWM [3] of 2·10-4, which should be equivalent to the box with a width of 2·10-4 George is using. Arun proposed that MCEEP is also used to analyze past experiments and check if it can reproduce the resolutions which were achieved there. The overall feeling was that the following should be done:
  1. use identical parameters to compare the GEANT and MCEEP simualtions.
  2. Check older data taken with point-like targets (no target effects expected), e.g. 16O(e,e'p) or recent 12C(e,e'p) runs.
  3. Check older data taken with extended targets, e.g. H(e,e'p).
In this frame there was also a discussion about the status of the OTR for monitoring the beam energy spread. Arun reported that the OTR is in, and we can use the OTR digitizer because Hall C is not running for most of the time. However, really utilizing the analyzer requires some experience.
[1] Marty checked on Saturday: running at 4.1GeV instead of 4.75GeV would not completely ruin the data point, though a lower beam energy means a larger scattering angle (loss in Mott) and a lower epsilon (loss in lever arm).
[2] Here is the table.
[3] In the meeting Marat reported a sigma of 2·10-4, which was commented to be much to wide, and he should use about 5·10-5. He checked later, and he had used a FWHM of 2·10-4.