Dear Steve,
when comparing dN/dEta distributions from
different energies should
we compare them at the same rapidity or the same
rapidity/(beam rapidity)?
Yours Michael
Quoting "Stephen J. Sanders" <ssanders@ku.edu>:
> 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
>
Michael Murray, Cyclotron TAMU, 979 845 1411 x 273, Fax 1899
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