Strangeness Production at SIS Energies

SQM 2007International Conference on Strangeness in Quark Matter

Xavier Lopezx.lopez@gsi.de

• 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 ρ0) 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

2ssu

2K

2K mOssuumm

2

1fm

GeV49.2E

GeV58.1E

K

,K

• 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. v1)

• Complex K- production mechanism

- strangeness exchange reactions: π + Y ↔ K- + B

- strong attractive potential (~ 70 MeV at ρ = ρ0)

- 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

K- stopped in 12C

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 (Bmodel = 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 7Li

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)

The FOPI Detector

• FOPI

- angular coverage close to 4π

- identification of fragments (1 < Z < 12)

- identification of p, d, t, 3He, 4He, , K

- reconstruction of resonances (, K0, , ,...)

• 2 high statistic experiments: study of strangeness production and propagation

- Ni+Ni and Al+Al at 1.9 AGeV (108 Evt, 10 TBytes)

πp→Λ -

Production of Λ and K0 in Ni+Ni at 1.9 AGeV

• High Λ and K0 statistics (> 4·104 counts) and huge rapidity coverage

- Λ/K0 produced at mid-rapidity

- K+/K0 KaoS - FOPI data in agreement

- Λ colder than protons and emitted from different region

• No kinetic equilibrium between Λ and p

IQMD model: C. HartnackM. Merschmeyer, X. Lopez et al. (FOPI), submitted to PRC (2007), nucl-ex/0703036

MeV780μ

MeV70T4080b

64

Al+Al

Λ and K0 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

Tm

T reff 2

3

23

2 20

K(892)

Strange resonances production

• Measurement of , K(892) and Σ(1385) in Al+Al at 1.9 AGeV

S = 185± 17S/B = 1.9MEAN = 1020 MeV/c2

σ = 4 ± 2 MeV/c2

Σ(1385)

(1020)

• First sub-threshold measurements

- K(892) (< 800 MeV)

- Σ(1385) (< 400 MeV)

1-2 counts/105 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) 4.3 50.7 39.4

c (fm) 46 4 5

Eth (GeV) 2.6 2.75 2.33

preliminary

Strange resonances and thermal model

6 independent ratios with 5 strange particles: p, π-, K0, (Λ+Σ0), , K*0(892) and Σ*±(1385) in Al+Al at 1.9 AGeV

- canonical ensemble (γs = 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 Tch ~ [70-80] MeV Difficult to get a clear picture from thesemodel assumptions

Need to include γs 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 AGeVwith 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 s½ = 2.7 GeV Data UrQMD

P(Σ*±)/P(Λ+Σ0)0.125 ± 0.026 (stat.)

± 0.033 (syst.)

0.177

P(K*0/K0)0.032 ± 0.003 (stat.)

± 0.012 (syst.)0.1

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 = ρ0

Γ = -2Im[Σ]Σ(1385) = 76 MeV

Mean mass: attractive potential ≈ - 45 MeV

Σ(1385) Al+Al

• Σ*±(1385) measurement in Al+Al s½ = 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

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/c2)

- bound state (H-dibaryons)

- partial inv. mass of heavier state (e.g. 4

ΛHe)

• Excess located to target rapidity region → cold protons

S-BSignal BKG

Target cm Proj.

Strange clusters could probe the cold and dense baryonic matter

FINUDA

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 m2 (150 MMRPC)

- channels: 4800

- t < 100 ps and < 0.5 cm

- PiD π±, K± up to p = 1 GeV/c

resonances productionK- flowsearch for strange clusters

K- and productionsearch 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 (2007-2009)

SQM 2007International Conference on Strangeness in Quark Matter

Xavier Lopez, x.lopez@gsi.de

The FOPI CollaborationBudapest (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