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Motivations Results on Σ (1385) with FOPI detector Results on Λ p correlation

Towards strange multi-baryonic clusters, measurement of Σ (1385) at SIS energies. Motivations Results on Σ (1385) with FOPI detector Results on Λ p correlation Conclusions / Outlook. X. Lopez for the FOPI Collaboration. R.J. Oakes, PR 131 (1963) 2239. R.L. Jaffe, PRL 38 (1977) 195.

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Motivations Results on Σ (1385) with FOPI detector Results on Λ p correlation

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  1. Towards strange multi-baryonic clusters, measurement of Σ(1385) at SIS energies • Motivations • Results on Σ(1385) with FOPI detector • Results on Λp correlation • Conclusions / Outlook X. Lopez for the FOPI Collaboration

  2. R.J. Oakes, PR 131 (1963) 2239 R.L. Jaffe, PRL 38 (1977) 195 K- +d reaction: the search for dibaryonsvia Λp correlations (1963-1985) Prediction of strange partner of the deuteron {10} (1963) and octet of dibaryons (1977): both cases assume H1+(Λp) Experiments show an excess at 2.13 GeV/c2. The major source of background proposed is ΣN interactions, H1+ not yet discovered. K-+d→π-+X+ 1.06GeV/c K-+d→π-+Λ+p at rest K-+d→π-+X+ 0.92GeV/c First excess measured in Λp inv. mass at 2.13 GeV (Γ=17 MeV) C. Pigot el al., NPB 249 (1985) 172 T.H. Tan, PRL 23 (1969) 395

  3. K- stopped on 4He, 7Li, 12C (2005-2006) T. Yamazaki and Y. Akaishi nucl-exp/0609041 M. Agnello et al., PRL 94, (2005) 212303 T. Yamazaki et al. Prediction of K- bound state to explain Finuda results (KeK) K- stopped in 7Li Controversies start on Λ(1405) description E. Oset et al., attributes the structure to final state interaction (FSI) → no peak in pp reac. K- stopped in 12C Excess in Λp inv. mass [2.2;2.3]GeV/c2 (Γ=67 MeV) V.K. Magas, E. Oset nucl-th/0601013

  4. With Heavy Ion Collisions A. Andronic et al., NPA 765 (2006) 211 Thermal model predicts a high production yield of anti-kaonic clusters in heavy ions collisions at SIS energies. Σ* • Λp correlations status: • Mass position unknown (M= 2.13, 2.25 GeV/c2) • Width unknown (Γ=17, 67 MeV) • Evaluation of the background complex • Need a reference analysis of ΛX correlations • Measurement of Σ(1385): • Known resonance: M=1.385 GeV/c2, Γ=40 MeV, Λπ at 88% • Σ(1385) measured by STAR in heavy-ion collisions • Therm. model predicts similar Σ* and cluster yields at SIS energies (P(Σ*/Λ)~10-2) SIS

  5. FOPI Detector at GSI • Angular coverage close to 4π • Identification of fragments (1 < Z < 12) • Identification of p, d, t, 3He, 4He, , K • Reconstruction of resonances (, K0, , ) • High statistic experiments performed • to study strangeness production: • Ni+Ni at 1.9 AGeV, 120 ·106 events (2003) • Al+Al at 1.9 AGeV, 400 ·106 events (2005) Λ

  6. Σ*± →Λ + π± (88%) p + π- (64%) Measurement of Σ(1385) with FOPI Al+Al 1.9 AGeV RHIC DATA: S.Salur, nucl-ex/0410039 THERM. MOD.: .A. Andronic, nucl-th/0511071 URQMD MOD.: M. Bleicher, NPA 715 (2003) 85 FOPI • First sub-threshold measurement of Σ(1385) • Input to fix +Y ↔ K-+B in medium • Fopi detector allows to reconstruct rare (raw yield ~10-5) and wide signal (Γ=40 MeV) STAR M = 1381 GeV/c2Г = 58 ± 7 MeV/c2

  7. Λp Invariant mass spectra from Ni+Ni collisions at 1.9 AGeV Λp in Ni+Ni • Excess found at 2.13 GeV/c2 • At limit of the significance • Structure present also in Al+Al collisions in the same mass region • Effect visible by a complete independent analyses → check of BKG construction (mixed event) in progress PRELIMINARY FINUDA • Excess at 2.13 GeV/c2: • Final state interaction (ΣN), dibaryons H1+(2113) ? • Flat distribution in [2.2;2.4] GeV/c2→ no evidence of the FINUDA structure

  8. Where is located the excessin phase space ? y0>-0.35 y0<-0.35 all Λp in Ni+Ni: y0=ycm -1 Enhancement of the signal by selecting rapidity far off the mid-rapidity (y0=0) Signal BKG S-B Excess distribution around the spectator region: need cold matter to form Λp clusters ? Target cm Proj.

  9. Conclusions / Outlook FOPI detector can identify wide and rare signals (Γ~40 MeV, P~10-3) • Evidence for signal of Σ*(1385) at SIS energies: (i) First sub-threshold measurement (second in HIC) (ii) Comparison to transport models calculations in progress • Λp correlations: (i) Excess found at 2.13 GeV/c2 from 2 different samples of data (ii) "Signal" located in the spectator region (iii) No evidence for FINUDA structure [2.2;2.3] GeV/c2 (iv) Cross check of independent analyses in progress • Ongoing analyses and experiment with FOPI: Other correlations are being analyzed: Λd, 3Heπ- , ... Experiment in 2007: A+A at 1.9 AGeV Program to study p+p at 3.5 GeV

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