Minutes of the E89044 group meeting September 17, 1999

Minutes of the E89044 group meeting, September 17, 1999, at Jefferson Lab

List of participants:

Konrad Aniol
Martin Epstein
Serge Kox
Michael Kuss
Dimitri Margaziotis
Jean Mougey
Gilles Quéméner
Arun Saha
Riad Suleiman
Paul Ulmer
Bogdan Wojtsekhowski

Due to hurrican Floyd several collaborators could not make it to the meeting. Thus, the agenda could not be followed exactly. It was decided that the next meeting will be held on Friday October 15, 1999.

Marty ...

... gave a brief introduction. He discussed the report Status of Preparations which was submitted to Kees the week before. The first paragraph dealt with the helium target. Michael reported that the transfer of the ³He from Bates to JLab was stalled due to some forms being missing. They are now in the local DOE office for signature. The amount will be about 4000 liters. The GWU ³He will not be available, Arun reported Barry Berman is reluctant because his contract forbids the use of the Helium before finishing his experiment. If neccessary, we will have to add Hall C ³He during the December running period.
Marty also discussed the items mentioned in the second half of the report:

Item b): The 4 GeV optics study for HRSE was done in August, Nilanga is analyzing it to get the matrix elements. Because there is still no optics study with a beam energy measurement, the spectrometer constants couldn't be redetermined.

[1]

Item d): E93050 (VCS) has demonstrated that the protons punching through the collimator can be separated by appropiate software cuts. These are cuts that require that the particles in both spectrometers originate from a common vertex in the target. Simulations done by George Chang show that an active collimator will do no better than the software cuts in eliminating proton punch through. Thus, the plans for installation of an active collimator are abandoned.
Item e): Marty reminded us that Jeff Templon's AEEXB simulations have demonstrated that one has to go to higher p_miss to study high E_miss unpolluted from the deuteron ground state radiative tail.
Item c): George Chang's Second Report on GEANT Simulation studies the target density effects on the E_miss resolution. George used for his simulation a beam energy spread of 2·10^-4 [2]. He also did a simulation for a target with one half the maximum density. Arun mentioned we have to be prepared if we cannot achieve the desired resolution with the nominal density.

Marty considers items a), c) and f) (luminosity and absolute cross section) as still to be resolved.

Marty ...

... reported for George Chang. From George's simulations it is not clear if we can separate the deuteron ground state from the break up channels. George's simulation contains a beam energy spread and energy loss of incoming and outgoing particles in the target material. It also contains radiative effects from external Bremsstrahlung, but not from internal and also no explicit broadening due to spectrometer resolution resulting from multiple scattering in the focal plane region. Arun commented that the intrinsic resolution of the spectrometers is of the order 10^-5 [3]. Clearly beam energy spread is important in obtaining good resolution and we need to consider ways to maintain a good quality beam. It was proposed to make a second, independent simulation using MCEEP. Paul said his code contains the different radiative and target effects including Landau straggling. However, it contains only the beer can type and not the tuna can type target shape. Marat and Riad will work on including the tuna can into MCEEP. It contains the spectral function for the ground state and break-up, one can run both channels separately or, with some trick, simultaneously. Marty volunteered to coordinate the simulation works of George (GEANT) and Riad and Marat (MCEEP).

Konrad ...

... showed how to monitor the luminosity and to normalize the cross section. His procedure is described in detail on the CalState web page. The problem is that there is no third spectrometer for luminosity monitoring like A1 at Mainz and also no possibility to normalize to the ³He elastic cross section at all Q² due to lack of precise data. Konrad's work-around is to measure at each setting the ³He elastic cross section at the most forward angle. These measurements will be repeated (same Q²) preferably at 1.245 GeV beam energy (see schedule). The setting at the lowest Q² will be linked to the world data and all other measurements to this one. The other spectrometer (HRSH) will be used as relative luminosity monitor to link the settings.
There was overall agreement to follow Konrads plan. It should be done independently of the effort UMass is putting into the developement of a luminosity monitor, in case the desired accuracy cannot be achieved. A detailed nomalization procedure has to be included into the run plan.
Bill Bertozzi's idea (mix a fraction of the ³He with a small amount of ⁴He) was not further investigated since the last meeting.

Michael

... reported on the cryo target status.

The purchase request for shipping Gerry Petersons ³He from MIT-Bates to JLab is out. Right now a form sheet for transfer of DOE property is in the local DOE office.
The target cell block was installed in March.
The gas handling system sits in the EEL almost completed and pressure tested.
Michael and Chris Keith of the target group are/will work on the target controls. Routines have to be added for the additional ITC502s for the GUI and for read-out of the gas panel status. It is not planned to operate the gas compressor remotely from the counting house.
The safety documents are to be prepared.
Gas handling operating procedures have to be developed.
Michael has to contact the cryogenic group on the status of switching between the 4K and 15K cryogen.

Arun ...

... presented the run schedule for December, February and March. Most of the time Hall C is not running, so we can utilize the Hall C laser to maximize the beam current in Hall A. He also showed the table of planned kinematics and pointed out that we need a detailed run plan which includes not only the times needed for physics settings but also for optics, normalization, beam energy and current, spectrometer angle and field setting etc. Also spectrometer pointing was discussed. Later in the afternoon we were told that the LVDT system used in E91026 (deuteron) and E93050 (VCS) will be installed again. It requires removal of the radiator. Alternatively/additionally we can determine the spectrometer mispointing by quasi-elastic ¹²C runs looking at y_tg position. On the energy measurement Arun reported that the ep system still does not work at low beam energies. For the ARC energy measurement, an additionally shielding on the first Compton quadrupole shadows the PMT used for the scanners 3 and 4, yielding a poor signal. A solution has to be found.

Gilles ...

... reported about the activities of the Grenoble group. Alain Romeyer studied Two or Three Epsilon Values for RLT Separation? His simulation showed, assuming the same finite amount of beam time available, that a third point does not help much. Here a controverse discussion started. It was agreed that the statement is correct in the absense of systematic errors but a third point may help understand systematic errors, by having all three points on a line. Michael recalled that we had the same discussion in one of the past meetings. There Shalev Gilad mentioned that a third point does not neccessarily mean a third epsilon but also can be a repeated measurement of the forward point to study systematic errors. The majority agreed that a third epsilon point is not needed.
Brian Tighe studied Acceptance Averaging Effects on the Determination of the Response Functions. He showed that one introduces a systematic error using different cut widths in the determination of the separated structure functions. However in most cases these systematic errors are small and are largest only on the smallest response functions. Arun commented that this is not the way the E89003 (Oxygen) analysis was done. They didn't average over the acceptance but separated into several bins before separation.
For Rosenbluth Separation in the Continuum Region Alain Romeyer proposed a new set of slightly modified kinematics. This report triggered some discussion on the E89044 mailing list. The point raised was to ensure keeping the omega-q matching of forward and backward point. Gilles discussed Tables 3 and 4 which you find on page 5 of the report. The Grenoble group will redo the tables, e.g. use one common electron momentum setting for the settings of Table 3, some differ only by a few 100 keV. Please send comments and concerns to Gilles Quéméner, Jean Mougey or Eric Voutier.

The Discussion about open tasks ...

... brought the founding of working groups. For each item one person is responsible as the leader. The few other people mentioned have already volunteered or were volunteered. Everybody willing to contribute please contact the responsible leader.

Sieve slit measurements: Nilanga Liyanage
Determination of final kinematics: Eric Voutier, Gilles Quéméner, Jean Mougey, Arun Saha, Marty Epstein
Detailed run plan: Konrad Aniol, Arun Saha, Jean Mougey, Michael Kuss, Nilanga Liyanage
omega-q matching: Kevin Fissum
Luminosity monitoring, absolute normalization: Konrad Aniol, Akio Hotta, Marat Rvachev
Hydrogen scattering: Riad Suleiman
Energy measurement, current calibration, pointing: Arun Saha, Nilanga Liyanage (Arun asked for volunteers who would like to learn how to perform energy measurements and current calibration. A separate email on this issue will follow)
Online data analysis: Gilles Quéméner, Marat Rvachev, Fatiha Benmokhtar, Marty Epstein, Michael Kuss, Riad Suleiman
Simulations: Marty Epstein, George Chang, Riad Suleiman, Marat Rvachev, Fatiha Benmokhtar, Eric Voutier
Target commissioning run plan: Michael Kuss, Konrad Aniol, Dimitri Margaziotis, Jian-Ping Chen
Shift assignment: Dimitri Margaziotis
Offline data analysis: Konrad Aniol, Marat Rvachev, Fatiha Benmokhtar

After the meeting:
[1] John LeRose: The spectrometers should be good for momenta as low as 100 MeV/c, at least. The NMRs may not lock anymore at momenta lower 400 MeV/c (or only the high field one). To accurately determine the momentum one has to calibrate the Hall probes against the NMR, with the field as close as possible to the desired field, and also as close as possible in time.
[2] George: ... used a square distribution with a width of 2·10^-4.
[3] Nilanga: Accounting for all the foils and air gaps the resolution in the middle of the focal plane should be about 0.5·10^-4. At the edges, however, the resolution should be only about 2·10^-4 due to the missing sextupoles.