Re: [Brahms-l] Stopping: Y/ybeam

From: Pawel Staszel <ufstasze@if.uj.edu.pl>
Date: Tue Dec 09 2003 - 15:53:41 EST
Hi Peter;
First of all we find the analysis a very nice piece of work.
However, we have a few comments on the draft dated on Nov. 26. 2003.

1. Regarding Michael's comments:
Equation (1) should be divided by N_part/2, rather then 197  because
we normalized the net baryon dN/dy to the number of participants.
This also means, that we restrict the rapidity loss only to the
inelastic NN processes. Maybe we should mentioned this explicitly
in the text.

Formula (2) should contain N_Labmda-LambdaBar, and also you have to correct
the description of the Eq. (2).

2. Looking at the requested by Michael plot of net dY/dy/y_beam it is
difficult to understand why there is the same
<dy>/y_beam at AGS and SPS - nevertheless this is what we can find in
the literature.

The quoted AGS and SPS values where obtained by  averaging dy over
rapidity range from 0 to y_beam with
measured net baryon dN/dy. You applied the same method (this can be
suspected from eq. (1)) which is consistent
with AGS and SPS points in terms of comparison made in Fig. 4.
  However, there is another method (which was applied both to AGS and SPS
data in Ref. [4]) that based on two Gaussian fit to the measured net
baryon dN/dy. The <dy> is therefore
related to the Gaussian centered at positive rapidity - and the
averaging range  can be from -inf to +inf.
  From [4] one can learn that the systematic uncertainty between both
methods is
15% for AGS (10.8GeV)  and 3% for SPS. This uncertainty
should vanish when the contribution to net baryon
from target and projectile are well
separated along the rapidity. So, one can expect that
for our data it is even less than 3%.
Moreover, we think that the second method is more suitable to use for
comparison between AGS, SPS and RHIC
energies because this method is not affected but the large overlap in
the mid-rapidity region.
It is also strange, that we use scaling factor of 0.64 from the fit to
AGS point ignoring the SPS
point which has a much smaller uncertainty related to the method applied.

3. You quote 5GeV/fm^3 for the energy density. From my estimates it is
about 4GeV/fm^3 assuming <E_t>=0.5GeV, Au radius 6 fm, tau_0 =1fm/c and
assuming that charged particles carry out 2/3 of the total energy.
However, now we know better <E_t> and it is rather larger than 0.5GeV.
Is it the reason for your estimates?

4. In the sentence: "...  at least 2 sigma from the K.",  we should
specify which
sigma and what does it mean K (probably the mean value of the K m^2
distribution).

5. Regarding the efficiency corrections for proton ID via RICH:
in the veto mode, certainly, you should subtract 5% of pions+kaons due
to inefficiency, but
above 15GeV/c you can better add 5% of identified proton yield.


Best regards
from Krakow group.

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Received on Tue Dec 9 09:49:42 2003

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