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    User name Jin Huang

    Log entry time 20:41:16 on July 05, 2010

    Entry number 330311

    This entry is a followup to: 330259

    keyword=Optics Check: Locating foils on optics target

    To clarify VZ problem reported in last log, more runs (1752-1764) are
    taken to scan beam vertical (y) positions. For each run, vz is
    constructed with LHRS and its preliminary database. Quality of
    reconstruction for central ray was demonstrated in Halog 329242
    (http://www.jlab.org/~adaq/halog/html/1007_archive/100701033232.html).
    
    For each run, there 4 plots are generated:
    * Left top: track angle at target (tg_th:th_ph) 
    * Right Top: momentun deviation (tg_dp) 
    * Left Bottom: vertex z vs tg_ph correlation
    * Right Bottom: vertical raster VS vertex z
    
    +y is up
    
    As Fig. 1, when beam was left at y=0, it's hitting some thick target at
    vz=~-15cm. Only down going particle was seen. Naive guess it's holder of
    upstream carbon foil. 
    
    For Fig. 2~3, beam was moved to -3 and -5mm, vz=-7.5cm(?) and +15cm foil
    has became more and more clear. Also, angular coverage has became more
    symmetric. 
    
    Therefore, a naive guess is when beam is at y=0, it's hitting foil
    holder. We should take more data at y=-5mm to get better vertical angular
    coverage as well as avoiding hitting the foil holder. 
    
    At y=-4 mm, more data was taken with raster off, which was shown in Fig
    5(LHRS) and Fig6 (RHRS). It seems vz peak at ~z=0- was much stronger than
    downstream carbon foil.  They both showed on RHRS VZ:tg_ph correlations,
    although less clear.
    
    It still confuses me why,
    1. beam y=0 was OK for 1 pass elastic run on LHRS, but now seems hitting
    holder. 
    2. There are only two vz peak at run 1762. One stronger than other. Could
    the stronger one be two foil or we lost the upstream carbon foil?
    3. Also for run 1762, there is a shadow on the small vz side (more upstream).
    
    


    A copy of this log entry has been emailed to: riordan, vasulk, schuster@slac.stanford.edu, ntoro@stanford.edu



    Figure 1: Run 1752, Beam y~0



    Figure 2: Run 1761, Beam y~-3mm



    Figure 3: Run 1762, Beam y~-5mm



    Figure 4: Run 1764, Beam y=-4mm, Raster off



    Figure 5: Run 1764 for R-HRS.