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or little Big Bang

Equilibration of Matter Near QCD Critical Point Larissa Bravina / Konrad Tywoniuk, University of Oslo. or little Big Bang. Content. Motivation. Why 40 AGeV? Conditions of thermal and chemical equilibrium Statistical model of ideal hadron gas Relaxation to equilibrium in central cell

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or little Big Bang

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  1. Equilibration of Matter Near QCD Critical Point Larissa Bravina / Konrad Tywoniuk, University of Oslo or little Big Bang

  2. Content • Motivation. Why 40 AGeV? • Conditions of thermal and chemical equilibrium • Statistical model of ideal hadron gas • Relaxation to equilibrium in central cell • EOS of hot and dense matter in the cell • Features of anisotropic flow around 40 AGeV • Summary and perspectives

  3. Motivation Why 40 AGeV?

  4. Equation of State Critical point is located around 10-40 GeV (LQCD) We have to explore this energy range to study the possible phase transition QGP can be formed already at low energies H. Stoecker, nucl-th/0506013 L. Bravina et al., PRC 60 (1999) 024904; 63 (2001) 064902

  5. Experimental Indications Onset of deconfinement or transition from baryon to meson dominated matter? M. Gazdzicki, nucl-th/0512034 J. Cleymans et al., Phys. Lett. B 615, 50

  6. Central cell: Relaxation to equilibrium

  7. Equilibration in the Central Cell Kinetic equilibrium: Isotropy of velocity distributions Isotropy of pressure Thermal equilibrium: Energy spectra of particles are described by Boltzmann distribution Chemical equlibrium:Particle yields are reproduced by SM with the same values of

  8. Statistical model of ideal hadron gas input values output values Multiplicity Energy Pressure Entropy density

  9. Pre-equilibrium Stage Homogeneity of baryon matter Absence of flow The local equilibrium in the central zone is quite possible

  10. Kinetic Equilibrium Isotropy of velocity distributions Isotropy of pressure Velocity distributions and pressure become isotropic at t=8 fm/c (for 40 AGeV)

  11. Thermal and Chemical Equilibrium Evolution of yields Energy spectra Thermal and chemical equilibrium seems to be reached... STEADY STATE

  12. Negative net strangeness density Net strangeness density in the central cell at 11 to 80 AGeV Net strangeness in the cell is negative because of different interaction cross sections for Kaons and antiKaons with Baryons

  13. Equation of State T vs. energy, etc

  14. Isentropic expansion Expansion proceeds isentropically (with constant entropy per baryon). This result supports application of hydrodynamics

  15. EOS in the cell energy vs. baryon density temperature vs. energy Infinite nuclear matter at normal nuclear density and zero net strangeness. Dense and hot equilibrated (almost) matter is formed Beginning of temperature ”saturation”

  16. EOS in the cell pressure vs. energy

  17. Elliptic flow of pions and protons at 40 AGeV Significant dip at midrapidity for proton flow in central events C. Alt et al. (NA49), PRC 68 (2003) 034903

  18. Elliptic flow of pions and protons at 40 AGeV However, the dip at midrapidity disappears if one uses the {2} or {4} cumulant method C. Alt et al. (NA49), PRC 68 (2003) 034903

  19. Elliptic flow of pions and protons at 40 AGeV

  20. Conclusions

  21. Summary and perspectives • There is a kinetic equilibrium stage of hadron-string matter in the central cell at t > 8 fm/c • The ratio P/e is approximately constant and equals 0.12 (AGS), 0.14 (40 AGeV), and 0.15 (SPS & RHIC) => onset of saturation • Entropy per baryon ratio remains constant during the time interval 8 fm/c < t < 20 fm/c. This supports application of hydrodynamics • Anisotropic flow at 40 AGeV : directed flow is nicely reproduced, while the situation with elliptic flow remains an open question

  22. Applicability of different models

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