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    User name horn

    Log entry time 07:54:52 on February 27,2004

    Entry number 437

    Followups:

    keyword=Events in tail of cointime main peak

    In order to examine the origin of the events observed as a "shoulder" to the left of the main peak in the coincidence time spectrum the missing mass distribution was examined. These events are clearly visible in a plot of of the missing mass as a function of coincidence time as shown in the left panel of Fig 1. Two types of events can be discerned. One type of event clearly reconstructs to the correct physical mass, but occurs earlier in coincidence time, the other type occurs in the tail of the missing mass distribution. Both types of events can be eliminated by cuts, but it needs to be determined whether these events correspond to valid physical events.



    First the events that reconstruct to the correct physical mass in the missing mass distribution will be considered. As shown previously, these events show up as a shoulder in the coincidence time spectrum and are correlated with (beta_tof-beta_p). Note that beta_tof refers to the velocity as measured from the time of flight whereas beta_p is calculated from the momentum. The dependence on beta-beta_p suggests that the particle was effectively slower as calculated from the time of flight: (beta-beta_p)<0. This could be attributed to nuclear interactions of pions in the scintillator producing hadrons. It should be noted that these pions were identified as such before reaching the scintillator and based on the theryofre missing mass reconstructs correctly. These events are eliminated by a cut on (beta-beta_p) which reduces the missing mass spectrum to the one shown in the right panel of Fig 1.



    The events occuring in the tail of the missing mass distribution constitute the remaining part of the "shoulder" observed in the coincidence time spectrum. As mentioned earlier, these events can be eliminated by a relatively loose missing mass cut. A larger value of the reconstructed missing mass suggests a modification in the kinematic variables used to calculate this quantity. In particular this could indicate a large energy loss of the pion. Comparing the data to the simulation seems to suggests that if there are pions that deposit a large amount of energy this event occured outside the acceptance.


    FIGURE 1

    FIGURE 2