Baryon Number Flow in High-Energy Collisions

Abstract

It is not obvious which partons in the proton carry its baryon number (BN). We present arguments that BN is associated with a specific topology of gluonic fields, rather than with the valence quarks. The BN distribution is easily confused with the difference between the quark and antiquark distributions. We argue, however, that they have quite different x-dependences. The distribution of BN asymmetry distribution is nearly constant at small x while q(x)-\bar q(x) \propto \sqrt{x}. This constancy of BN produces energy independence of the \bar pp annihilation cross section at high energies. Recent measurement of the baryon asymmetry at small x at HERA confirms this expectation. The BN asymmetry at mid-rapidities in heavy ion collisions is substantially enhanced by multiple interactions, as has been observed in recent experiments at the SPS. The same gluonic mechanism of BN stopping increases the production rate for cascade hyperons in a good accord with data. We expect nearly the same as at SPS amount of BN stopped in higher energy collisions at RHIC and LHC, which is, however, spread ove larger rapidity intervals.