[Brahms-l] A short comment on stopping models

Hi,

At QM NA49 has shown some comparisons to UrQMD calculations that seems to 
reproduce the trends seen in rapidity loss, see the parallel talk by C. 
Blume.

This is in my opinion a postdiction and one argument for why it is not 
always a good idea to quote postdictions by models as real understanding 
is to look at the paper:
Baryon junction loops and the baryon-meson anomaly at high energies
Phys. Rev. C 70, 064906 (2004) (11 pages)

If you look at Figure 6 in the paper you will see that all the model 
calculations describe the data perfect, but if you look at the data they 
have used and compare to our data you will see that their net-baryons at 
y=0 are around 10 while ours are around 15. They have misunderstood the 
correction we mention *2/3 to get feeddown corrected protons and *2 to get 
net-baryons, BUT NOT BOTH AT THE SAME TIME!

So their model can apparently pretty much describe everything.... and 
maybe they should have thought a little bit more about the huge 
disagreement they get with our energyloss calculation on the page before 
even though the fit curves looks similar to their model curves!

I mentioned this to Flemming one year ago and was surprised that not 
everybody in BRAHMS knew about this. I think it is an important point, 
because you clearly see that model calculations needs a lot of 
(correct:-) data to be constrained.

Cheers,
    Peter

:-) --------------------------- )-:
  Peter H L Christiansen
:-D --------------------------- \-:
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