1. Strangeness Production at SIS Energies SQM 2007 International Conference on Strangeness in Quark Matter Xavier Lopez x.lopez@gsi.de

2. Introduction The FOPI Detector Strange resonances in medium Search of strange multi-baryonic states Conclusions / Outlook Strangeness Production at SIS Energies

3. In medium effects could be induced by a partial chiral symmetry restoration Decreasing part of quarks condensate Beam energy close or below the production threshold of strange particles High baryonic densities (2-3 ρ 0 ) reached during a relatively long time (~ 10 fm/c) The physics of strangeness at SIS (2 AGeV) SIS B. Friman et al., EJPA 3 (1998) 165 W. Weise, Prog. Theor. Phys. Suppl. 149 (2003) 1

4. K + and Y essentially produced via secondary reactions: Δ + N → K +,0 + Y + B K +,0 produced during the earlier stage of the collision (high densities) - repulsive potential (KN ~ 20-30 MeV from diff. v 1 ) Complex K - production mechanism - strangeness exchange reactions: π + Y ↔ K - + B - strong attractive potential (~ 70 MeV at ρ = ρ 0 ) - coupled in the medium with Σ(1385), Λ(1405) and Λ(1520) Strangeness at SIS: Production mechanisms M.F. M. Lutz et al., NPA 700 (2002) 309 C. Hartnack nucl-th/0507002

5. K - stopped in 12 C V.K. Magas, E. Oset nucl-th/0601013 Akaishi and Yamazaki: K - N bound-state of -27 MeV prediction of the existence of K - pp state K - pp → p + Λ + 263 MeV B = 48 MeV, Γ = 60 MeV Measurement: FINUDA peak at 2.25 GeV and Γ = 67 MeV (B model = 115 MeV) Weise and Doté: absorption KN→ πΛ, πΣ KNN→ ΛN, ΣN K - NN state of Γ = 100 MeV, B = 60 MeV Magas and Oset: final state interaction Therm. model: abondance of kaonic clusters ~ strange resonances yields at SIS K - N potential: prediction of bound states T. Yamazaki and Y. Akaishi nucl-exp/0609041 M. Agnello et al., PRL 94, (2005) 212303 K - stopped in 7 Li Search for KNN bound states in HIC at SIS energy A. Andronic et al., NPA 765 (2006) 211 A. Doté and W.Weise hyp2006 nucl-th/0701050 N.V. Shevchenko et al., Phys. Rev. Lett. 98, 082301 (2007)

6. The FOPI Detector FOPI - angular coverage close to 4π - identification of fragments (1 < Z < 12) - identification of p, d, t, 3 He, 4 He,  , K  - reconstruction of resonances ( , K 0, , ,...) 2 high statistic experiments: study of strangeness production and propagation - Ni+Ni and Al+Al at 1.9 AGeV (10 8 Evt, 10 TBytes)

7. Production of Λ and K 0 in Ni+Ni at 1.9 AGeV High Λ and K 0 statistics (> 4·10 4 counts) and huge rapidity coverage - Λ/K 0 produced at mid-rapidity - K + /K 0 KaoS - FOPI data in agreement - Λ colder than protons and emitted from different region No kinetic equilibrium between Λ and p IQMD model: C. Hartnack M. Merschmeyer, X. Lopez et al. (FOPI), submitted to PRC (2007), nucl-ex/0703036

8. Al+Al Λ and K 0 in Ni+Ni and Al+Al at 1.9 AGeV Test of kinetic and chemical equilibrium kinetic temperature - strange particles systematically colder than non-strange hadrons - radial flow in Ni+Ni, almost no expansion in Al+Al - same kinetical freeze-out temperature in Al+Al and Ni+Ni (~ 90 MeV) thermal model reproduce ratios with T ~ 70 MeV - kinetical T ~ 90 MeV > chemical T ~ 70 MeV ?? - limited number of particle species - need to extend the study to strange resonances production: , K(892), Σ(1385),... THERM. MOD.:.A. Andronic et al., NPA 772 (2006) 167

9. K(892) Strange resonances production Measurement of , K(892) and Σ(1385) in Al+Al at 1.9 AGeV S = 185± 17 S/B = 1.9 MEAN = 1020 MeV/c 2 σ = 4 ± 2 MeV/c 2 Σ(1385)  (1020) First sub-threshold measurements - K(892) (< 800 MeV) - Σ(1385) (< 400 MeV) 1-2 counts/10 5 events ! X. Lopez et al. (FOPI), submitted to PRL (2007) short life time resonances should probe finite density   K + + K - K* 0  K + +  - Σ* ±   +  ± Γ (MeV)4.350.739.4 c (fm)4645 E th (GeV)2.62.752.33 preliminary

10. Strange resonances and thermal model 6 independent ratios with 5 strange particles: p, π -, K 0, (Λ+Σ 0 ), , K* 0 (892) and Σ* ± (1385) in Al+Al at 1.9 AGeV - canonical ensemble ( γ s = 1) - adding resonances increase T - the  is not describe at all - chemical T ε [70;80] MeV < kinetical T (90 MeV) Taking into account strangeness production at SIS leads for T ch ~ [70-80] MeV Difficult to get a clear picture from these model assumptions Need to include γ s in the model (fit the  ) ? Measurement with an heavier system ? preliminary A. Andronic, private communication

11. Strange resonances and transport model Σ* ± (1385) and K* 0 (892) in Al+Al at 1.9 AGeV with UrQMD model (M. Bleicher, S. Vogel) - no in medium effect (cascade mode) - production time t ~ 7-8 fm - reconstruction at t ~ 12-15 fm - dominant production channel: 70% K+π→K* σ ~ 20 mb 30% N*(∆)+B →K* 76% Λ+π→Σ* σ ~ 37 mb 12% Σ+π→Σ* 12% N*(∆)+B →Σ* Al+Al s ½ = 2.7 GeVDataUrQMD P(Σ* ± )/P(Λ+Σ 0 ) 0.125 ± 0.026 (stat.) ± 0.033 (syst.) 0.177 P(K* 0 /K 0 ) 0.032 ± 0.003 (stat.) ± 0.012 (syst.) 0.1 Σ*Σ* K* preliminary Yield of K*(892) over-estimated → measurements allow to fix limits on Kπ & Λπ fusion cross section within this model

12. Strange resonances and Chiral theory Σ* ± (1385) and the Chiral Unitary theory (E. Oset) Σ(1385)→Λπ(Σπ) at ρ = ρ 0 Γ = -2Im[Σ] Σ(1385) = 76 MeV Mean mass: attractive potential ≈ - 45 MeV Σ(1385) Al+Al Σ* ± (1385) measurement in Al+Al s ½ = 2.7 GeV - no broadening observed (PDG values with errors) - relevance to have a measurement of Σ(1385) from heavier systems Murat M. Kaskulov, E. Oset, PRC 73 (2006) 045213 Need to include spectral function in transport codes

13. KNN clusters: search for Λp correlations Excess observed in Ni+Ni and Al+Al with significance ~ 5 Interpretation unclear - final state interaction - ΣN interaction (2.13 GeV/c 2 ) - bound state (H-dibaryons) - partial inv. mass of heavier state (e.g. 4 Λ He) Excess located to target rapidity region → cold protons S-B Signal BKG Target cm Proj. Strange clusters could probe the cold and dense baryonic matter FINUDA

14. FOPI upgrade and scheduled experiments Heavy ion program (2007-2009) - Ni+Ni and Ni+Pb at 1.9 AGeV - Ru+Ru at 1.69 AGeV Elementary processes (2007-2009) - π beam on p and Pb at 1.7 GeV/c - p beam on p/d at 3 AGeV FOPI ToF Upgrade: MMRPC - size: 6 m 2 (150 MMRPC) - channels: 4800 -  t < 100 ps and   < 0.5 cm - PiD π ±, K ± up to p = 1 GeV/c resonances production K - flow search for strange clusters K - and  production search for strange clusters

15. Conclusion / Outlook Strangeness physic at SIS energies with new probes from the medium ! - sub-threshold measurement of K(892), Σ(1385) resonances - K - potential and the  production are not understood - strange multi-baryonic states could probe the cold and dense medium - measurements of resonances from heavier system are already scheduled (2007-2009)

16. SQM 2007 International Conference on Strangeness in Quark Matter Xavier Lopez, x.lopez@gsi.de The FOPI Collaboration Budapest (Hungary) Bucharest (Romany) Clermont-Ferrand (France) Darmstadt (Germany) Dresden (Germany) Heidelberg (Germany) Lanzhou (China) Moscow (Russia) Munich (Germany) Seoul (South Korea) Split (Croatia) Strasbourg (France) Vienna (Austria) Warsaw (Poland) Zagreb (Croatia)

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