Strangeness Production at SIS Energies SQM 2007 International Conference on Strangeness in Quark Matter Xavier Lopez

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

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

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 ~ 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/

K - stopped in 12 C V.K. Magas, E. Oset nucl-th/ Akaishi and Yamazaki: K - N bound-state of -27 MeV prediction of the existence of K - pp state K - pp → p + Λ 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/ M. Agnello et al., PRL 94, (2005) 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/ N.V. Shevchenko et al., Phys. Rev. Lett. 98, (2007)

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)

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/

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

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) c (fm)4645 E th (GeV) preliminary

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

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 ~ 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 ) ± (stat.) ± (syst.) P(K* 0 /K 0 ) ± (stat.) ± (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

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) Need to include spectral function in transport codes

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

FOPI upgrade and scheduled experiments Heavy ion program ( ) - Ni+Ni and Ni+Pb at 1.9 AGeV - Ru+Ru at 1.69 AGeV Elementary processes ( ) - 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:  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

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 ( )

SQM 2007 International Conference on Strangeness in Quark Matter Xavier Lopez, 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)

THE END

Conclusion / Outlook Measurement of resonances in Ni+Pb s ½ = 2.7 GeV - highest beam kinetic energy / projectile mass - enhancement of the number of nucleons in the target - best compromise between s ½ and ρ - better acceptance/ PiD of kaons K -, , K(892), Σ(1385),... K clusters: Λp and Λd corr. chiral predictions (e.g. Σ(1385), ,...) higher statistics of K(892) and  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 - measurement of resonances from heavier system

with gamma s

Directed flow of K + P. Crochet et al., PLB 486 (2000) 6 Ru+Ru 1.69 AGeV Study of integrated sideward flow of K + : absence of K + flow doesn't due to columbian repulsion (K 0 ) co-production of K + and Λ but different propagations Study of differential sideward flow of K + : anti-flow at low p t and flow at high p t good agreement with the version of model which take into account a repulsive K-N potential (~ 20 MeV) Evidence of in medium effects on K + propagation J.L.Ritman et al., ZPA 352 (1995) 355

Consistent results between FOPI and KAOS Sign of V 2 for K + and K - show in-medium effect The trend of V 2 for K + and K - is different compared to the models Elliptic flow of Kaons A. Mishra et al. PRC 70(2004) in plane out of plane Y-J. Kim, to be submitted to PRL KAOS data: F. Uhlig et al. PRL 95(2005) K+K+ K-K- Ni+Ni at 1.93 AGeV

Rapidity distribution of K - /K + ratio: enhancement of the ratio at mid-rapidity version of the model which take into account an attractive (repulsive) potentials for K - (K + ) reproduce the data K - /K + ratio function of the number of participant: constant for a light system (Ni) decrease for heavy system (Au) Ambiguity for the evidence of in medium effect on K - production Strangeness exchange reaction could be the reason:  +Y ↔ K - +B K - /K + ratio K. Wisniewki et al., EPJA 9 (2000) 515 A. Förster et al., PRL 91 (2003) AGeV

Strangeness exchange reactions A. Förster et al., nu/ex Transport model predict a later time production of K - with respect to K + → different emission time caused by  +Y ↔ K - +B (Y=Λ, Σ) Centrality and system size dependence similar for both K + and K - Experimental results and models predictions confirm that strangeness exchange reactions are the dominant process for K - production → Need to extend the study of production and propagation of strangeness to other particles species: K 0, Λ, Σ(1385),... α=1.25±0.12 α=1.22±0.27 α=1.26±0.06 α=1.34±0.16 α=1.0±0.05 α=0.96±0.05 N+Δ→K + +Λ+p π+Λ→K - +N

Summary and perspectives Adams et al., PRC 71 J(2005) FOPI Al+Al PRELIMINARY ? RHIC DATA: STAR Collaboration, PRL 97 (2006) THERM. MOD.:.A. Andronic, NPA 772 (2006) 167 URQMD MOD.: M. Bleicher, NPA 715 (2003) 85 X. Lopez et al., to be submitted to PRL

K(892) with K + π - in 1.9 AGeV K*K* K*K* BW FIT Adams et al., PRC 71 J(2005) F FIT Effect of PS function: colder temperature ↔ high Inv. Mass Mean Value of P t = 422 MeV "Freeze out temperature": T fo = 65 MeV Final parameters (mass, Γ) in agreement with PDG

Measurement of K(892) with FOPI First sub-threshold measurement of K(892) at SIS energy Mean and width in agreement with PDG Time production ~7 fm/c Dominant channel in UrQMD K+π→K* Thermal(transport) models under(over)- predicts the K(892)/K 0 yields ratio A temperature of 70 MeV does not reproduce ratio with resonances K *0 K + +π - (2/3) K 0 +π 0 (1/3) cτ = 4 fm E th =2.75 GeV PDG: Mass = 896 MeV Γ = 50 MeV K + + π - Al+Al 1.9 AGeV DATATherm. (T=70 MeV) UrQMD P(K* 0 /K 0 )0.0383± PRELIMINARY

Σ(1385) in transport model UrQMD (M. Bleicher-S. Vogel) Ratio at production time (~10 fm/c) P(Σ* - +Σ* + )/P(Λ+Σ 0 ) = Ratio with reconstructable Σ* (>200 fm/c) P(Σ *- +Σ *+ )/P(Λ+Σ 0 ) = ~8% π Σ* lost in inelastic rescattering Σ* creation processes 76% Λ+π→Σ* σ ~ 37 mb 12% Σ+π→Σ* 12% N*(∆)+B →Σ* Single yields are in agreement with the data Similar rapidity distributions for Σ and Λ Data σ geo ≤315 mb: P(Σ *- +Σ *+ )/(Λ+Σ 0 )=0.125±0.026(stat.)±0.033(syst)

K(892) in transport model UrQMD (M. Bleicher-S. Vogel) Ratio at production time (~10 fm) P(K *0 )/P(K + +K 0 ) = Ratio with reconstructable K* 0 (>200 fm and in K + +π - ) P(K *0 )/P(K + +K 0 ) = ~4% π K* lost in inelastic rescattering K* creation processes Data σ geo ≤315 mb preliminary : P(K *0 )/(K + +K 0 )=0.021±0.005(stat.)±(syst.→P. Velten) 70% K+π→K* (σ under calculation) 30% N*(∆)+B →K*

Kaonic Cluster predictions Clusters of anti-kaons : K - bind with nucleus with strong interaction Hypothesis of discrete states of this objects High binding energy (~100 MeV) New state of the matter Densities could reach 10 times the normal nuclear density Y. Akaishi et al., PRC 65 (2002) T. Yamazaki et al., PLB (2002) A. Doté et al., PRC 70 (2004) V.K. Magas et al., nucl-th/ E. Oset et al., nucl-th/ BUT theoretical controversies !

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

A. Andronic et al., NPA 765 (2006) 211 SIS Σ* Σ* Search for kaonic clusters in heavy ions collisions Thermal model predicts a high production yield of anti- kaonic clusters in heavy ions collisions at SIS energies Decay channels of clusters of anti-kaons accessible with FOPI Excess found at 2.13 GeV/c 2 - limit of the significance - final state interaction (ΣN), dibaryons H1 + (2130) ? - flat distribution in [2.2;2.4] GeV/c 2 → no evidence of the FINUDA structure Structure present also in Al+Al collisions in the same mass region Excess distributed around the spectator region: need cold matter to form Λp clusters ? FINUDA Ni+Ni 1.93 AGeV ΛpΛp

Kaonic clusters in heavy ions 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 Decay channels of clusters of anti-kaons accessible with FOPI : Excess found on Λd analysis, but cluster mass range unknown Need to test analyses on ΛX correlation already measured → Σ*(1385) Resonances measured in heavy ions collisions (RHIC, S. Salur et al., J.Phys. G31 (2005) S179 ) Thermal model predicts similar Σ* and clusters yields at SIS energy (P(Σ*/Λ)~10 -2 ) SIS PRELIMINARY Ni+Ni, 1.93 AGeV

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)

K - N interaction is dominated by sub-threshold resonances () KN potential and states

K * with K AGeV) DATA K+K+ K*K* NEVT= NK + =411941±641 NK * =5792±950

Al+AlNi+Ni Raw yields: ~ 2 times more Λ (due to N events) in Al and S/B better (factor 2.6) for the same set of cuts Λ selected for Σ * analysis in Al & Ni data 10<TMUL<33 25<TMUL<58