5. Strange enhancements

Particle enhancement versus strangeness content for various particles produced in lead­lead (Pb­Pb) and proton­beryllium (p­Be) collisions. The enhancement for a particular particle is defined as the number of that particle produced per participating nucleon in Pb­Pb collisions, divided by the number produced per participating nucleon in p­Be experiments. There is an enhancement of 1.3 for all non-strange particles, h^­, in these collisions; these are mainly negative pions that do not contain any strange quarks. Such enhancement is natural in a quark­gluon plasma and can also be accounted for by conventional reaction scenarios. However, the production of particles that contain one strange quark, such as the neutral kaon (K_S⁰) and the lambda particle, is enhanced by a factor of about three; the enhancement factor rises to about five for the doubly strange xi particle (and its antiparticle, the anti-xi), and to about 15 for the omega particle, which contains three strange quarks, and its antiparticle. The particles in the right panel have no valence quarks in common with the projectile nucleons (e.g. an anti-lambda contains three antiquarks, including one strange antiquark). These results were obtained by considering particles emitted at "mid-rapidity" in 158 GeV per nucleon Pb­Pb interactions. The data are from the CERN WA97 experiment.

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