Figure. The mid-rapidity strange particle yields versus the negative hadron yield as measured by STAR in Au-Au collisions at sqrt(s)=130 GeV. All measured particles reveal a smooth, near linear, increase.

One of the original Quark Gluon Plasma (QGP) signatures was that of a large increase in strange particle production. The liberation of quarks and gluons within a QGP means that quark anti-quark pairs can be created without the need to expend extra energy creating the other quarks required to bind them into hadrons. The strange quark mass is ~150 MeV, whereas the energy needed to produce a strange quark in a hadron gas is at least 530 MeV via pi + N -> Lambda + K and that to produce an anti-strange quark requires ~1.5 GeV through K + pi -> anti-Lambda + N. As the QGP cools quarks are once again bound within hadrons but the increased s quark yield remains. Therefore it was predicted that, should heavy-ion collisions result in QGP formation, a dramatic rise in strange particle yields would be observed. It is expected that only the more central events produce a medium that is sufficiently hot and dense so as to produce conditions suitable for the phase transition. As the centrality of the collision is believed to be correlated with the scale of particle production a sudden jump in the strange particles yields versus the charged hadron yield could be taken a possible evidence of QGP formation. As we can see there is a smooth, near linear, increase in all strange (anti)particle yields as a function of produced negative particles at mid-rapidity as measured by STAR at sqrt(s)=130 GeV.

Mid-rapidity Lambda and Lambda bar Production in Au + Au Collisions at sqrt(s_nn) = 130 GeV
Phys. Rev. Lett. 89 (2002) 092301
e-Print Archives (nucl-ex/0203016): Abstract | PS | PDF
Journal article: Phys. Rev. Lett. server

Kaon Production and Kaon to Pion Ratio in Au + Au Collisions at sqrt(s_nn) = 130 GeV
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e-Print Archives (nucl-ex/0206008): Abstract | PS | PDF
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Multi-strange baryon production in Au-Au collisions at sqrt(s_nn) = 130 GeV
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e-Print Archives (nucl-ex/0307024): Abstract | PS | PDF
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