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Strangeness Production at SIS Energies
SQM 2007International Conference on Strangeness in Quark Matter
Xavier [email protected]
• 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, [email protected]
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