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

K - +d→π - +Λ+p at rest T.H. Tan, PRL 23 (1969) 395 K - +d reaction: the search for dibaryons via Λp correlations ( ) C. Pigot el al., NPB 249 (1985) 172 R.J. Oakes, PR 131 (1963) 2239R.L. Jaffe, PRL 38 (1977) 195 K - +d→π - +X GeV/c K - +d→π - +X GeV/c 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/c 2. The major source of background proposed is ΣN interactions, H1 + not yet discovered. First excess measured in Λp inv. mass at 2.13 GeV (Γ=17 MeV)

K - stopped in 12 C M. Agnello et al., PRL 94, (2005) V.K. Magas, E. Oset nucl-th/ T. Yamazaki and Y. Akaishi nucl-exp/ E. Oset et al., attributes the structure to final state interaction (FSI) → no peak in pp reac. K - stopped on 4 He, 7 Li, 12 C ( ) T. Yamazaki et al. Prediction of K - bound state to explain Finuda results (KeK) Excess in Λp inv. mass [2.2;2.3]GeV/c 2 (Γ=67 MeV) Controversies start on Λ(1405) description K - stopped in 7 Li

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. SIS Σ* Σ* Λp correlations status: Mass position unknown (M= 2.13, 2.25 GeV/c 2 ) 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/c 2, 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 )

FOPI Detector at GSI 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, ,  ) High statistic experiments performed to study strangeness production: Ni+Ni at 1.9 AGeV, 120 ·10 6 events (2003) Al+Al at 1.9 AGeV, 400 ·10 6 events (2005) Λ

Measurement of Σ(1385) with FOPI RHIC DATA: S.Salur, nucl-ex/ THERM. MOD.:.A. Andronic, nucl-th/ URQMD MOD.: M. Bleicher, NPA 715 (2003) 85 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) Σ* ± → Λ + π ± (88%) p + π - (64%) STAR FOPI Al+Al 1.9 AGeV M = 1381 GeV/c 2 Г = 58 ± 7 MeV/c 2

Λp Invariant mass spectra from Ni+Ni collisions at 1.9 AGeV Excess found at 2.13 GeV/c 2 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 Λp in Ni+Ni Excess at 2.13 GeV/c 2 : Final state interaction (ΣN), dibaryons H1 + (2113) ? Flat distribution in [2.2;2.4] GeV/c 2 → no evidence of the FINUDA structure FINUDA PRELIMINARY

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

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/c 2 from 2 different samples of data (ii) "Signal" located in the spectator region (iii) No evidence for FINUDA structure [2.2;2.3] GeV/c 2 (iv) Cross check of independent analyses in progress Ongoing analyses and experiment with FOPI: Other correlations are being analyzed: Λd, 3 Heπ -,... Experiment in 2007: A+A at 1.9 AGeV Program to study p+p at 3.5 GeV Conclusions / Outlook