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    User name A. Deur

    Log entry time 01:44:43 on August11,2003

    Entry number 110062

    This entry is a followup to: 108004


    If, as it seems from the 4.2 GeV 6 degree analysis the pions are coming from the glass window getting into the acceptance due to multiple scattering, (see entry 108004), then we should see almost pions from C12 runs.
    I compared a He3 run at kinematics 8:15 with the C12 run.
    The pi/e ratio for He3 is 40%
    The pi/e ratio for C12 is 30%
    So the ratio is a little less but not much so, assuming that the pi/e ratio don't change significantely with the target material (no EMC effect !), this contradict the previous assumption about pion originating from glass and coming in by multiple scattering.
    Also, if this was true, I would have expect less pions at 9 degree, which does not appear to be true.

    I look at the yt origin of the pions. It still seems it comes from the windows. In fig 1, I put yt without pid cut (left) and with anti-pid cuts to keep only the pions (right plot). The top plots are for a He3 cell while the bottom ones are for an empty cell. The shoulder for the He3 plot is largely enhanced by anti-pid cuts, showing a large pion production from the window. The anti-pid cut has almost no effect on the empty ref cell run.

    In fig 2, we see clearly that most of the events from the empty ref cell run are indeed pions: The top plot shows a preshower vs shower plot for He3 run and the bottom plot is a run for the empty cell run.

    So it seems clear where the pions are coming from (mostly) the windows. But it is not clear how the make it to the acceptance.

    FIGURE 1

    FIGURE 2