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

From: Peter H. L. Christiansen <pchristi@nbi.dk>
Date: Fri Dec 12 2003 - 10:57:28 EST
Hi Pawel 

I introduced most of your comments into the text.

> 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.

I'm looking into this now. It is at least clear that the values in the 
plot before were incorrect. I think that here in Copenhagen we would 
prefer to use equation 1 on the double gauss fit so that we treat AGS, 
SPS, and RHIC in the same way. I think the idea with the double gaus is 
very nice, but it is for a longer paper I feel.
I try to get the values fromn E917 for the fit-parametrization.  

> 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?
I put 5 Gev/fm^3 to be consistent with the high-pT paper. This value was 
calculated by JJ using the E-T from Djam and my analysis and t-o = 1fm/c 
and the overlap geometry.

Cheers
   Peter

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Received on Fri Dec 12 10:57:54 2003

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