Does anyone know any way of estimating the net baryon density in collision experiments, e.g. in LHC, RHIC, or the upcoming ones at GSI-FAIR?

I have comes across many hand-waving arguments, sample -

  1. Electron-positron colliders start with $\rho_B = 0$, and since conservation laws have to respected, matter and anti-matter must be produced in equal amounts. Hence, barring inhomogeneities, LHC is essentially in the $\rho_B \approx 0$ regime.

  2. Antikaon-proton interaction is known to be attractive, through various model-dependent calculations, so if we have a ${\bar K}-p$ collision experiment, it shall involve the formation of quasi-matter having a larger density than usual, and hence, via these kind of reactions, GSI-FAIR plans to study QCD matter at high densities (especially in the Compressed Baryonic Matter experiment), while it remains inaccessible at LHC.

(Please correct me if the hand waving is inappropriate.) I am wondering, if there is any way of making this a little more calculation oriented, though I understand that a fully rigorous calculation would be very difficult. (I don't want that, too.)

Also, is it possible to have any model-independent answers, since model-dependent answers can be found with a bit of googling, e.g. Phys. Rev. C 72, 034613 (2005), which even has the evolution of these densities in lead-lead collisions. Though these calculations are the order of the day, model-independent calculations, if possible, teach you much more.

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    $\begingroup$ The answer is no, imo. Either you develop a model that you can calculate which will be fairly complicated as it is many body on many body scattering ( arxiv.org/abs/1205.0579 ), or you hand wave. $\endgroup$
    – anna v
    Commented Jun 1, 2014 at 7:31
  • $\begingroup$ @ anna v - Thanks, at least some one responded. I completely buy the fact that a rigorous calculation is very complicated. But since you are an experimentalist in particle physics (if I'm right), you are in good position to assess these arguments. Is my understanding of FAIR's high density experimentation correct? Is this the right hand-waving argument for how these guys plan to reach all these fantastic densities ($\sim 4$ times the nuclear saturation density). Thanks :) $\endgroup$
    – 299792458
    Commented Jun 1, 2014 at 10:37
  • $\begingroup$ @ anna v - I'm not thrusting the issue that it necessarily has to be this K-p business. It is a popular version that people `sell' in casual conversations. I gave that example since I felt, you were in a better position to judge as compared to me, on the basis of your background. Thanks :) $\endgroup$
    – 299792458
    Commented Jun 3, 2014 at 6:58
  • $\begingroup$ see , back in the 1970's my thesis was on K-proton scattering at 7 GeV , so I am curious of the claim you gave. At high energies K- and K+ scattering crossections converge. $\endgroup$
    – anna v
    Commented Jun 3, 2014 at 7:01
  • $\begingroup$ My casual reflection is that at you can't see any of this at 7 GeV! These are typically low energy experiments. No intention to compete with the `high' energy colliders. $\endgroup$
    – 299792458
    Commented Jun 3, 2014 at 7:04


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