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I have a question regarding the nature of the particle spectrum at ALICE as a function of momentum. The spectra in question can be seen here.

My question is, why is it that the particle spectrum in the low momentum range is rising, then reaching a maximum and then beginning to decrease again. From what I have understood it has something to do with the Fermi theory of beta decay. It would be awesome it anyone knew and you give me a hint on it.

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  • $\begingroup$ Is it just me or did they really go with this illegible font? $\endgroup$ – Demosthene Mar 19 '15 at 16:50
  • $\begingroup$ Out of curiosity, have you looked at the papers referenced? The hydrodynamic model is not something I am familiar with, but it may explain some or all of the structure seen here in relatively simple terms. Of course the plot is of non-trivial complexity: its a double differential cross-section as a function of transverse momentum at for maximally central events. Presumably each of those facts (double differential; depending on transverse momentum; maximally central events) are important. $\endgroup$ – dmckee --- ex-moderator kitten Mar 19 '15 at 17:18
  • $\begingroup$ I have tried to look at hydrodynamic model, but can't find anything about it. I was thinking that it may be because of the collision, that High momentum particles are unlikely and the low momentum particles are Also unlikely because of the forces and the limited energy avaliable. But i have no Clue why $\endgroup$ – Morten Sode Mar 19 '15 at 17:30
  • $\begingroup$ High-A collision physics is far enough outside my specialization that I hesitate to say anything. I think that maximum centrality implies roughly equal Borjken-x for the active partons, but that is as far as my knowledge goes. $\endgroup$ – dmckee --- ex-moderator kitten Mar 19 '15 at 17:37
  • $\begingroup$ Maybe it's just me, but I would think that the rise & fall just be an effect of the cross section increasing (causing the rise) then the particle population decreasing (causing the decline). $\endgroup$ – Kyle Kanos Mar 19 '15 at 21:01

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