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Hypernucleus Formation in High-Energy Nuclear Collisions

Hypernucleus Formation in High-Energy Nuclear Collisions. T. Gaitanos , H. Lenske, U. Mosel. Introduction The Giessen-BUU (GiBUU) transport model Formation of fragments and hyperfragments Applications Heavy-Ion-Collisions (A+A@3AGeV) Final remarks & outlook.

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Hypernucleus Formation in High-Energy Nuclear Collisions

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  1. Hypernucleus Formation in High-Energy Nuclear Collisions T. Gaitanos, H. Lenske, U. Mosel • Introduction • The Giessen-BUU (GiBUU) transport model • Formation of fragments and hyperfragments • Applications • Heavy-Ion-Collisions (A+A@3AGeV) • Final remarks & outlook DPG-Frühjahrstagung, 12-16 März 2007 mit dem Fachverband: Hadronen und Kerne work supported by BMBF

  2. Main topic of this talk Outlook, in progress… Introduction… • At high  hyperons may play an important role in neutronstars Consequence: modified EOS modified masses and radii… • Knowledge of the Y-N and YY interaction? • So far mainly from nuclear structure single-L hypernuclei near stability region • Info on hyperons in neutron rich matter/nuclei needed • Study of hypernucleus in reactionsexotic Hypernuclei Wakai,Bando,Sano, PRC38(1988)748,Wakai, NPA547(1992)89c, and others… • Hypernucleus production accessible in reactions (future experiments): Heavy-Ion-Collisions (HypHI-project, GSI) Antiproton-Nucleus (PANDA-project, GSI)

  3. K L L,S,p,K,... L p p L L L,S,p,K,... K Relativistic Hypernuclei… • Production of Hypernuclei in Relativistic HIC • Production of many hyperons • Secondary rescattering (pNYK) • Multiple coalescence of hyperons with fragments • Theoretical Framework • Phase-Space evolution • (Transport equations of Boltzmann type) • Description of fragment formation ? • (Statistical models of fragment formation (GEM), coalescence models…) • Furihata, NIMB171 (2000) 252… • Hirenzaki et al., PRC48 (1993)2403,Sato/Yasaki, PLB98 (1981)153…

  4. Collision integral • Full coupled channel problem • 61 baryons & 21 mesons in the code • (Manley, PRC29(1984),PDG) More info http://www.physik.uni-giessen.de/GiBUU/ The (Giessen-BUU) GiBUU Transport Model… • Transport Equations of Boltmann type for hadrons • Non-Relativistic (Skyrme-MDI), • Relativistic (Non-Linear Walecka Models, NL2)connection to nuclear structure drift mean field “Lorentz Force”→ Vector Fields pure relativistic term → Relativistic Equations of motion for xm and p*m for „test particles“ + collisions +

  5. Phase-space coalescence model… Fixed energy, N/Z dependence Fixed N/Z, energy dependence • Global fit of coalescence parameters to experimental charge distributions • Problems: de-excitation, sequential decay & evaporation not included…

  6. Coalescence+De-Excitation… De-excitation: Generalized Evaporation Models (in progress…) Alternative-1: simple Coalescence Alternative-2: decay of „hot“ fragments into nucleons & light clusters (d,t,…) Alternative-3: decay of „hot“ fragments according their „probability“ W=Ebind/E (E: Excitation energy)

  7. Heavy System Light System Formation Mechanism of Hyperfragments… Hyperons formed from high- phase rescattering with „spectator“-particles  In collisions of heavy nuclei (Au) difficult separation from pion-background (fireball)  captured by cold „spectator“-clusters with high probability, e.g. 4,6He  Possible in collisions of light systems (Ca+Ca,C+C) without problem of pion-background (Fireball)

  8. Heavy System Light System Hyperfragments vs. Coalescence Methods…  Important sensitivity to the coalescence procedure  Hot fragments do not servive in standard coalescence  Inclusion of excited clusters increases probability of hypernucleus formation

  9. Heavy System Light System Hyperfragments vs. Nuclear Mean-Field… •  Moderate sensitivity to the Nuclear Mean-Field • RMF-NL2 more repulsive (strong momentum dependence)less compressionless Hyperons • In Skyrme MD saturates at high energiesless repulsionmore compressionmore Hyperons • More systematic analysis (include Hyperon-MF from Nuclear Structure…)

  10. Conclusions & Outlook… • Hypernucleus Formation in Relativistic HIC •  Hypernucleus production with moderate probabilities •  Particularly important separation from “coctail”-background • in collisions of light systems • Sensitivities •  Phase-Space Coalescence • (needs comparison with data!) •  Mean-Field dynamics moderately affects Hypernucleus production • In progress •  More sophisticated models of Nuclear Structure • (Density-Dependent Hadronic Field Theory for Baryons…) •  Performe same Analysis also for Antiproton-Nucleus Collisions (PANDA) •  Inclusion of Evaporation Models (GEM) important… •  Inclusion of Nucleon-Antinucleon cross sections…

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