Figure. The mid-rapidity, pt integrated, anti-baryon/baryon ratio in Au-Au
collisions at sqrt(s)=130 GeV compared to that in Pb-Pb collisions at
Anti-baryon to baryon ratios are close to unity
The anti-baryon to baryon ratio supplies information about the amount of
baryon transfer from the colliding nuclei to the central collision region.
At RHIC there is a gap of 12 rapidity units between the two beams.
Therefore a baryon needs to be transported through 6 units of rapidity to
be observed at mid-rapidity. The proximity of the anti-baryon/baryon ratio
to unity tells us that the net baryon number is close to zero at
mid-rapidity for Au-Au collisions. At RHIC the anti-proton to proton ratio
at colliding energies of 130 GeV/c is measured by STAR to be 0.71, which
means that 70% of the protons are produced via pair production. This is
very different to the measurements made at SPS where nearly all the
measured protons are derived from the colliding nuclei.
The ratios increase with increasing strange quark content of the
particles and have been shown to be approximated by a multiplicative factor
given by the K+/K- ratio. This trend is predicted by quark coalesence and
Related STAR papers
Strange anti-particle to particle ratios at mid-rapidity in sqrt(snn) = 130 GeV Au + Au collisions
Phys. Lett. B 567 (2003) 167
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