Re: Draft multiplicity paper. BRAHMS 200AGeV.

From: Stephen J. Sanders (ssanders@ku.edu)
Date: Mon Oct 22 2001 - 17:23:30 EDT

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    Hi,
      As JJ has indicated, the 200 mult paper running on a fast track and we 
    hope to have a
    final version by the time JJ gets back  (JJ is the principal author of 
    the current
    draft).  While undergoing the hardship of a meeting
    in Mali (Hawaii), I did have a chance to chat with Kharzeev concerning his
    calculations and the overall question of model comparisons.  He brought up
    several points, in particular, that we need to consider for the "next" 
    draft:
    1)  The Hijing Npart numbers are known to differ from the Glauber values for
    more peripheral events.  The reason for this discrepancy is apparently 
    not well
    understood, since Hijing uses Glauber to calculate these numbers.  In 
    any case, Phobos,
    Phenex, and Kharzeev now all have the same Npart numbers based on Glauber.
    The clear suggestion is that we also adopt the newer (correct?) numbers.
    2)  For central collisions, Npart is modified (increased) due to quantum 
    fluctuation.
    This increase is NOT accounted for in the present calculations and, 
    therefore,
    when the theory curve shows a "flat" dependence of 2*(dN/deta)/Npart vs. 
    Npart for
    central events, the data are expected to rise as Npart increases because 
    of the
    fluctuations.  (Motto, theorists are crafty...).  This suggests to me 
    that an attempt
    to fit a functional form like A*Npart + B*Ncol may not be very useful.
    3) Both Kharzeev and Wang have suggested that what IS useful is the ratio
    of the 200/130  (dN/deta)/Npart results.  Here we can expect scaling 
    errors of the
    experiment and some inadequacies of the theory (such as fluctuation) to 
    partially cancel.
    Hiro is working on this figure now and we expect a new draft with the 
    revised figures
    by mid-week.
    
    While moving the discussion of the draft from the paper committee to the
    "committee of the whole" is undoubtly burdensome, the hope is that getting
    feedback early will speed up the final submission.   These results are 
    clearly
    of great interest to the community. (...and, we are not the only group 
    that has
    done this measurement...)
    
    Regards, Steve
    



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