Minutes of the E89044 group meeting, April 24, 1999, at Jefferson Lab

List of participants:

Konrad Aniol
George Chang
Kevin Fissum
Akio Hotta
Michael Kuss
Dimitri Margaziotis
Arun Saha
Marat Rvachev
Xiaodong Jiang
Bogdan Wojtsekhowski

Arun Saha ...

... openend the meeting. He presented the experiment schedule for the run time of E89044 (comment: as of Saturday, the accelerator energy was 0.9 GeV on the schedule for February 2000. Monday, it was decided in the scheduling meeting to run with 0.95 GeV, as requested by E89044.).
Octavian Filoti, student of Bill Hersman, will participate. See the list of students.

Topic a.: Arun Saha ...

... announced that Javier Gomez will give a detailed talk on the next collaboration meeting. He reported that the LVDT system gives an accurate angle but the spectrometer pointing cannot be reproduced satisfactorily. Here, the accuracy is about 2-3 mm. Arun mentioned that we need to know by about August if we will have a reliable system or not.

Topic b.: George Chang ...

... presented GEANT simulations studying particle punch-through the collimators. As an example, he used the kinematics in the first line of Tab. 2. Electrons don't establish a problem, they don't punch through the collimator. 1.148 GeV protons loose about 360 MeV. Reconstructing missing mass (missing energy) one finds that the ground state (nd) is shifted to about 260 MeV/c². Thus, the continuum at lower M_miss is free of contamination of punch through. However, a more realistic simulation is needed. George will repeat including partial punch through the edges due to long target.

Topic c.: Kevin Fissum ...

... gave a report on the status of simulation programs. Paul Ulmer and John LeRose included SNAKE transport into MCEEP. This allows several apertures in the magnetic system giving a realistic acceptance space. An other modification would be to include a radiative tail simulation into MCEEP, this is not planned right now.
Gilles Quéméner has his own version of MCEEP. He used acceptance functions obtained during E93050 (vcs), and he also put coordinates transport from target up to focal plane using COSY tensors. As a kind of by-product, there will soon be SPIN tensors from COSY.

Topic d.: General discussion ...

... about targets. Michael Kuss reported for Nilanga Liyanage. As a by-product from the optimization of the data base for E93050 he deduced from the E_miss width a spectrometer momentum resolution of about 5*10^-4, assuming the resolution of both HRSs is similar. This is not too bad, compared to 2.5-4*10^-4, achived with the waterfall target. There was a discussion about pro and cons of tuna can opposed to beer can. This discussion was started by other experiments who want to run even higher luminosities. George Chang mentioned that his simulations (comment: now that there is a feeder scanner in Heathers office all the transparacies/copies will be scanned and put on the web. Please allow some time) show that a tuna can has a (marginally) better M_miss resolution. Dimitri Margaziotis mentioned that a prototype was manufactured long time ago, it should be somewhere at JLab. There were concerns that a beer can target will have much more problems with heating due to gas flow parallel to the beam.

Topic e.: Michael Kuss ...

... reported that the Helium gas handling system will allow interchange of ³He with Hydrogen. Thus, we can think of using Hydrogen for acceptance/normalization studies.

Topic g.: Arun Saha ... ... will rerun the kinematics optimizer using the new beam energies and settings.

Topic h.: Marat Rvachev ...

... spoke about the data base optimization he did for E94010 (GDH). E89044 will need optics studies because the highest momentum in HRSE will be 3.96 GeV/c, significantly higher than for E93050 who derived matrizes at 3.0 and 3.5 GeV/c. The differences between both matrizes are small, but beyond 3.5 GeV/c saturation effects should start to play a role. Also, moving the elastic peak over the focal plane cannot be achieved by changing the field, as at low momentum, but by changing beam energy (impractical) or spectrometer angle (may cause a drop in cross section at larger angle). Also, we need a stack of foil targets for y_tg optimization. Three ideas were presented:

• Michael Kuss tested a 2mil KAPTON foil parasitically. There were 2µA beam current for about 5min and 5µA for about 3min on the target. The circular raster was 4mm in diameter. Though calculations guided that the foil should melt the rate was still ok at the end of the test. Thus, the test should be repeated with beam on the target for about one hour, e.g. during an EP measurement. The typical rates will be about 0.2 Hz, taking into account that KAPTON has only 2.6% of Hydrogen. The rates will be increased by using thicker KAPTON foils and having a stack of them, but still they will be low. Additionally, changing to sieve slit will reduce the count rate by a factor of 100. Also, there is not much space on the dummy target ladder attached to the cryo targets.
• Kevin Fissum proposed thinking of the waterfall target. Each fall has a thickness of about 150 mg/cm². Also, it can be used with any beam current, unrastered. The count rate estimate gives at least an improvement of a factor 100 compared to KAPTON. However, the status of the waterfall target is unknown, and though it can be modified to have more falls it is unclear how much work this requires. Additionally, the cryo target would need to be removed first, the waterfall target installed and commissioned, thus the dedicated time needed at least a month.
• Bogdan Wojtsekhowski proposed to place a thin Tungsten slit collimator close to the Hydrogen target. The slits simulate a Hydrogen foil stack. Advantage is that it would not require a target modification. A mechanism is needed to move the collimator in and out, reproducable. Also, it has to be surveyed.

Topic i.: Akio Hotta ...

... reported about luminosity monitoring. The goal is to have a system with a rate proportional to the luminosity. It would be nice to have a third spectrometer like at A1/Mainz. Non-magnetic spectrometers are swamped by background and are not precise enough. One idea would be to monitor pd photo-disintegration, which should be a clean signal. The ³He(e,e) cross section beyond 1 GeV/c is not well enough known to achieve an accuracy of 2%, as mentioned in a previous meeting.

Bogdan Wojtsekhowski ...

... explained his plan to install an additional trigger detector plane, S0. It will be placed between S1 and the gas Cerenkov. The plane will not be segmented, only one paddle, and read-out on both sides. A test is planned to check if low energy particles may be detected in both S1 and S0. If, then the distance between those planes has to be increased.