Transcript Slide 1

SQM 2007
International Conference on
Strangeness in Quark Matter
Strangeness Production
at SIS Energies
Xavier Lopez
[email protected]
Strangeness Production
at SIS Energies
• Introduction
• The FOPI Detector
• Strange resonances
in medium
• Search of strange
multi-baryonic states
• Conclusions / Outlook
The physics of strangeness at SIS (2 AGeV)
In medium effects could be induced
by a partial chiral symmetry restoration
m 2K f K2  
SIS
 
1
m u  ms  uu  ss  O ms2
2
• Decreasing part of quarks condensate
W. Weise, Prog. Theor. Phys. Suppl. 149 (2003) 1
• Beam energy close or below the production
threshold of strange particles
E K  ,  1.58 GeV
E K   2.49 GeV
• High baryonic densities (2-3 ρ0) reached
during a relatively long time (~ 10 fm/c)
B. Friman et al., EJPA 3 (1998) 165
Strangeness at SIS: Production mechanisms
C. Hartnack nucl-th/0507002
• 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)
M.F. M. Lutz et al., NPA 700 (2002) 309
K-N potential: prediction of bound states
• 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
K- stopped in 7Li
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
T. Yamazaki and Y. Akaishi
nucl-exp/0609041
A. Doté and W.Weise hyp2006 nucl-th/0701050
N.V. Shevchenko et al., Phys. Rev. Lett. 98, 082301 (2007)
M. Agnello et al.,
PRL 94, (2005) 212303
K- stopped in 12C
• Magas and Oset: final state interaction
• Therm. model: abondance of kaonic
clusters ~ strange resonances yields at SIS
A. Andronic et al., NPA 765 (2006) 211
V.K. Magas, E. Oset nucl-th/0601013
Search for KNN bound states in HIC at SIS energy
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)
Λ → p  π-
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
M. Merschmeyer, X. Lopez et al. (FOPI), submitted to PRC (2007), nucl-ex/0703036
IQMD model: C. Hartnack
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 ??
Teff 
2  m0
3 
r 2  T 

3 2
2 
T  7064 MeV
40
μ b  78080
MeV
Al+Al
- 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
Strange resonances production
• Measurement of , K(892) and Σ(1385) in
Al+Al at 1.9 AGeV
 
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
(1020)
±
preliminary
S = 185± 17
S/B = 1.9
MEAN = 1020 MeV/c2
σ = 4 ± 2 MeV/c2
• First sub-threshold measurements
- K(892) (< 800 MeV)
K(892)
Σ(1385)
- Σ(1385) (< 400 MeV)
1-2 counts/105 events !
short life time
resonances should
probe finite density
X. Lopez et al. (FOPI), submitted to PRL (2007)
Strange resonances and thermal model
A. Andronic, private communication
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 these
model assumptions
Need to include γs in the model (fit the ) ?
Measurement with an heavier system ?
preliminary
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 ~ 12-15 fm
- dominant production channel:

76% Λ+π→Σ* σ ~ 37 mb
Σ* 12% Σ+π→Σ*
K*

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
70% K+π→K* σ ~ 20 mb
30% N*(∆)+B →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) 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
Need to include spectral
function in transport
codes
Murat M. Kaskulov, E. Oset, PRC 73 (2006) 045213
Σ(1385)
Al+Al
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. 4ΛHe)
• Excess located to target
rapidity region → cold protons
FINUDA
Signal
BKG
Strange clusters could probe the
cold and dense baryonic matter
Target
cm
Proj.
S-B
FOPI upgrade and scheduled experiments
• 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
• Heavy ion program (2007-2009)
- Ni+Ni and Ni+Pb at 1.9 AGeV
- Ru+Ru at 1.69 AGeV

resonances production
K- flow
search for strange clusters

K- and  production
search for strange clusters
• Elementary processes (2007-2009)
- π beam on p and Pb at 1.7 GeV/c
- p beam on p/d at 3 AGeV
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 2007
International Conference on
Strangeness in Quark Matter
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)
Xavier Lopez, [email protected]
THE END