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    User name jpchen

    Entry time Mon Aug 16 18:11:52 EDT 1999

    Entry number 71

    keyword=Minutes of 8/11 analysis meeting and angle inf summary

    Present: Alexandre Deur, Pibero Djawotho,Marat Rvachev, Xiaodong Jiang, Haiyan Gao, Jian-ping Chen.
    Seonho is on the phone from Temple.

    Seonho: Productions completed for all the inelastic He3 runs.
    Working on a program to check runs, so that the students can use to go through all the data.

    Alexandre: This week I worked mainly on the elastic asymmetry at 0.8 GeV (2 DAQ).
    It turns out that the big jump (that cannot come frome statistical fluctuations)
    do not appear in the raw assymetry computed from scalers. So it's easy to
    correct them and the asymmetry at 0.8 GeV, after this correction, looks pretty
    good: they are close to the expected value but I have not the definitive value
    of the NMR (they are not expected to change, Steffen is working on it) and I did
    only the cross section average correction. I still have to do the acceptance
    correction, quasi elatic correction and radiative correction (but as the breakup
    is far away in comparison to 1.7 GeV, the correction should be smaller), the
    detector efficiency correction and the N2 dillution.
    It's still not clear what cause these big jump. It's a
    deatime-like correction to give but I don't know yet why we have to do it ? Bob
    Michael told me this effect was seen before (for exemple by Nilanga) and is due
    to frequent beam trip. But the beam current is very stable for run 2855 (the run
    that need the biggest correction). Unless I did a mistake in plotting, the beam
    look to have no trip during run 2855. I am investigating the deatime now to see
    if there is a correlation between the bad runs and a strange deatime beahavior.
    The helicity affectation looks fine (we are not throwing away events because of
    a indefined helicity as people strongly supposed at the begining).
    I went back also at the asymetries at 1.7 GeV (1 DAQ). We have
    to do the same correction also in the case of 1 DAQ (for some reason it's less
    important that at 0.8 GeV). The correction looks the same for electron and
    hadron arms. The corrections on the 1.7 GeV elastic asymmetry are visible but
    not dramatic. they did raise a little bit the experimental averaged asymmetry
    (but it's not systematic: for 0.8 the correction make the averaged one smaller).

    Some discussion followed the presentation.For the questionable run (Run2855)
    there is a online note that it has dead time problem. Why the deadtime has
    helicity correlation is unclear. It could be just fluctuations that when deadtime
    jumped high (many time during the run), it happened to be more in one helicity
    state than the other one. During that period whenever tape copying (to mass storage)
    was going, deadtime jumped high and fluctuated a greatly. Several runs during that
    period have similar problems.

    Pibero: Showed a plot of N2 yield vs. P.
    Discussion on how to make the N2 dilution corrections. Will need to know the
    N2 percentage in the He3 target cell (either from the measurement during filling
    or from comparison of N2 elastic peak from the He3 cell vs. from the reference N2 cell).

    About the H-arm spectrometer angle and offset: After disucssion with Javier and
    the survey group, we found that the only survey done before the experiment was the 9/12
    survey when the spectrometer was at 12.2 degree and the spectrometer was moved to
    37 degree and moved back to 15.5 degree before the GDH data taking start. So the only
    information on the angle and the pointing (from the start to 11/, when the spectrometer
    moved) is from the encoders.There are two encoders for each spectrometer.
    Unfortunately one of the h-arm encoders was (and still is) not working reliablly.
    However, this will be our only information. The encoder readings give the spectrometer
    angle and pointings which are displayed in the spectrometer EPICS window.

    Following is a summary of the spectrometer angles and pointings during the GDH experiment:
    9/25-10/6 10/6-12/12 12/12-12/13 12/13-12/24
    E-Spectrometer angle:(degree) 15.485 15.503 17.492 15.495
    E- Pointing (Horizontal)(mm): 2.67 -0.36 -- 0.48
    (Upstream is positive)
    E- Vertical (mm) (up=positive) -- 0.62 -- 0.58
    Good for Runs: 1621 3216/20550 20580 20607/3480

    H-spectrometer angle: 15.528 15.528 12.526 15.508
    H- Horizontal Pointing: -3.8 -3.8 -- -1.11
    (Upstream=positive)
    H- Vertical pointing: -- -- -- 0.82
    Good for Runs up to: 1621 3216 3271 3480