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Therese Renstrøm

Strangeness enhancement as a signal of Quark-Gluon Plasma and a signal of the onset of deconfinement. Therese Renstrøm. Confinement Deconfinement, asymptotic freedom Quark-Gluon Plasma. Fig.1 The effective coupling constant in QCD,

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Therese Renstrøm

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  1. Strangeness enhancement as a signal of Quark-Gluon Plasmaanda signal of the onset of deconfinement Therese Renstrøm

  2. Confinement • Deconfinement, asymptotic freedom • Quark-Gluon Plasma Fig.1 The effective coupling constant in QCD, dependence of momentum exchange between the interacting hadrons

  3. QGP Fig. 2 An incredibly simplified picture of the creation of Quark-GluonPlasma • How to get so hot and dense? • Answer: Ultrarelativistic heavy ion collisions

  4. Signatures of Quark-Gluon Plasma • Electromagnetic probes (direct photons and dileptons) • J/psi-suppression • High pT suppression • Jet modification and correlations • Elliptic flow • Strangeness enhancement

  5. Strangeness Content: for matter at thermal and chemical equlibrium Schwinger model for particle production gives production probability In a nucleon-nucleon collision the ratio of strange to non-strange pairs is ca 0.1 Strangeness in hadron gas Counting the valence quarks of kaons and pions, gives the relation In nucleon-nucleon collision this ratio is very small (p-Be, ratio=0.05)

  6. Strangeness in hadron gas at thermal and chemical equilibrium • What about nucleus-nucleus collisions? • Produced hadrons: mainly pions and kaons • What is the ratio of strange to non-strange pairs if it is allowed to reach thermal and chemical equlibrium? • Obtain strangeness content fraction by treating the system of pions and kaons as an electrically neutral(!) boson gas in thermal and chemical equlibrium • Use of Bose-Einstein statistics, and setting the chemical potential to zero is justified.

  7. Now we can express the density one type of meson as The above intergral leads to the result Where K2 is the Bessel function of order 2

  8. At temperature T=200MeV Notice that the summands of the two sums converge rapidly Considering only the first summand in both sums, corresponds to using the Maxwell-Boltzman distribution And following the ratio of strange to non-strange particles: Notice that the ratio is considerably enhanced! (0.05 for p-Be)

  9. Strangeness in QGP in thermal and chemical equlibrium • Strangeness content in QGP is governed by the dynamical state of the plasma • Thermal equilibrium- momentum distribution of particles do not change • Chemical equilibrium- densities of particles reach steady state • What are the densities of the different kinds of quarks if the plasma has a lifetime long enough to establish thermal and chemical equlibrium?

  10. Quarks = fermions, using Fermi-Dirac statistics We have the following number density of one type of quark Current mass, sincedeconfinement The presence of an antiquark corresponds to the absence of a quark in a negative energy state, so

  11. Looking at chemical potential equals zero, we see that the predicted number density of s quarks equals that of u and d quarks. Gives a strange/nonstrange ratio of 1/2! Strongly suggests strangeness enhancement as a signature of QGP!

  12. Approaching chemical equilibrium in QGM So what are the mechanisms of strange pair production in QGP?

  13. Fig. Lowest order Feynman diagrams for strange anti-strange production from quark antiquark annihilation (a) and gluon fusion (b),(c),(d).

  14. Cross-sections for the reactions

  15. Rate of production of strange anti-strange pairs from quark annihilatons and gluon fusion

  16. So, the final expressions for the rate of production per unit space-time are: Notice the similarites of the these two integrals. The cross sections are of the same order of magnitude, The difference between the Fermi-Dirac and the Bose-Einstein distribution functions are negible at high temperatures,

  17. The main difference comes from the degeneracy factors We can conclude that the main source of strangeness production in QGP comes from gluon fusion This was theoretically predicted by J.Rafelski and B.Muller in 1982

  18. The equalibration time of the strangeness production The knowledge of the equilibrium strange quark denstity and the rate of change gives us an estimate of the equilibration time

  19. Phase-transitions Strangeness as a way of determining the order of phasetransition

  20. The kink, horn and step • Three characteristics were predicted to exist if the fasetransition from the hadron gas to QGP was of first order • The theory was tested experimentally of the NA49-collaboration • The experimental results confirmed the theory

  21. The kink Fig. Energy dependence of the mean pion multiplicity per wounded nucleon.

  22. The horn Fig. Energy dependence of the <K+>/<π+>

  23. The step Fig. Energy dependence of the mean inverse slope parameter T for K+ spectra.

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