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Hyperon Polarization in Heavy ion Collisions

Hyperon Polarization in Heavy ion Collisions. C. C. Barros Jr. Universidade Federal de Santa Catarina Brasil. Strangeness in Quark Matter 2013 University of Birmingham. 1976 – Bunce et al. ( Phys . Rev. Lett . 36, 1113). 300 GeV. A totally unexpected result –

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Hyperon Polarization in Heavy ion Collisions

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  1. HyperonPolarization in HeavyionCollisions C. C. Barros Jr. Universidade Federal de Santa Catarina Brasil Strangeness in Quark Matter 2013 Universityof Birmingham

  2. 1976 – Bunceet al. (Phys. Rev. Lett. 36, 1113) 300 GeV A totallyunexpectedresult – Polarizationeffectsshoudvanishat Highenergies (theoreticaland experimental expectative)

  3. In thefollowingyears – many data for Y (L,S,X)andantihyperons (E761,...) Andother...

  4. Polarization in pA Collisions • Hundredsof GeV • Normal to theproduction plane • Be, ... • Hyperonandantihyperon

  5. Polarization in pA Collisions • A verychallengingproblem. • Manymodels: - OPER - Quark recombination - Lund strings - Constituent quark models... • Explainthe data, butthere are problems, specially for theantihyperons (mostofthesemodels does notapply) • Y. Hama, T. Kodama (1993) – Hydrodinamical elements+ optical potential – final state interactions

  6. Collision Hot expanding Hadronic matter (final stage) Final particle interactions (and statistical fluctuations)

  7. TheModel - Hydrodynamical aspects + • LowenergypYfinal-stateinteractions (the relative energy is small) • Most of the produced particles are pions – this is the dominant interaction (for baryons) • It is a indirect production mechanism

  8. LowEnergypYInteractions • Few data for theseinteractoins • Effectivechirallagrangians – a goodchoice (describe quite wellpNandNN lowenergyinteractions) • Treediagrams + sigma term (loop) • Manyintermediateparticlesconsidered (resonances, mesons...)

  9. LowEnergypYInteractions

  10.  Interaction

  11. Some loops

  12. Coupling Constants Sigma term results

  13. interactions results - At low energies the cross Section is dominated by the S(1385) resonance. • Similar behavior for the other Hyperons

  14. LowEnergypYInteractions HyperCP (2003/2004) - (X decays -Fermilab) (Chakravorty et al. , Phys. Rev. Lett. 91, 031601) Calculations (C.C.Barros Jr and Y. Hama, Phys. Rev. C (2001))

  15.  Interaction

  16. Interaction

  17. Rapidity Distribuitions Produced pions (inside the fluid) Fluid

  18. Rapiditydistributions Data – W. Bell et al., Z Phys, C 27, 191 (1985)

  19. Reactions

  20. Final Polarization

  21. Final Polarizations

  22. dependence

  23. AA Collisions • STAR data (Abelev et al. 2007) – Global polarization Noncentral relativistic nucleus-nucleus collisions possesses large angular momentum Angular momentum of the system, L, is Defined normal to the reaction plane Reaction plane is determined by the beam direction and the impact parameter b

  24. AA Collisions • Some models are availabe (previous talks, for example) • These system is a interesting place to apply the model • BRHAMS pseudorapidity distributions are used to determine the fluid propreties and hydrodinamical parameters

  25. Velocitydistribution - Fluid (longitudinal and transversal expansion) Particlesinsidethe Fluid (pions) Observedparticles Distribution

  26. RHIC It is possible to obtain quite well the parameters BRHAMS data 200 GeV Au-Au PHENIX data

  27. Polarization (the effect of final-state interactions) STAR data – Abelev et al. Phys. Rev. C 76 024915 (2007) One more time shows that the results are consistent

  28. LHC Perspectives • With the presented mechanism, for LHC systems, for all Hyperons and Antihyperons the Global polarization (for many reasons, b, incoherent processes...) Large angular momentum effect?

  29. LHC Perspectives • pA collisions? • It could be possible to find a small polarization, in the production plane • At the moment it is just a conjecture, the calculations are not ready yet...

  30. Conclusions • A model that works to produce polarization in pA collisions is considered (hydro+final-state interactions) • Significant in “old” pA collisions • Global Polarization is almost totally washed out in AA collisions – compatible with the RHIC data • LHC pA collisions? • Where to find? Normal to production plane at small angles (a possibility)

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