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
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
- measurement of resonances from heavier system
• Measurement of resonances in Ni+Pb s½ = 2.7 GeV
- highest beam kinetic energy /
projectile mass
K-,  , K(892), Σ(1385),...
- enhancement of the number of
nucleons in the target
K clusters: Λp and Λd corr.
- best compromise between s½
and ρ
chiral predictions (e.g. Σ(1385), ,...)
- better acceptance/ PiD of kaons
higher statistics of K(892) and 
with gamma s
Directed flow of K+
Ru+Ru 1.69 AGeV
P. Crochet et al., PLB 486 (2000) 6
Study of integrated sideward flow of K+ :
• absence of K+ flow doesn't due to columbian repulsion (K0)
• co-production of K+ and Λ but different propagations
Study of differential sideward flow of K+ :
• anti-flow at low pt and flow at high pt
• good agreement with the version of model which take into
account a repulsive K-N potential (~ 20 MeV)
J.L.Ritman et al., ZPA 352 (1995) 355
Evidence of in medium effects on K+ propagation
Elliptic flow of Kaons
A. Mishra et al. PRC 70(2004) 044904
Y-J. Kim, to be submitted to PRL
Ni+Ni at 1.93 AGeV
K+
in plane
out of plane
KAOS data: F. Uhlig et al. PRL 95(2005) 0123101
K-
• Consistent results between FOPI and KAOS
• Sign of V2 for K+ and K- show in-medium effect
• The trend of V2 for K+ and K- is different compared to the models
K-/K+ ratio
1.5 AGeV
K. Wisniewki et al., EPJA 9 (2000) 515
A. Förster et al., PRL 91 (2003) 152301
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
Strangeness exchange reactions
A. Förster et al., nu/ex 0701014
α=1.26±0.06
α=1.34±0.16
M ~ Aαpart
α=1.25±0.12
α=1.22±0.27
α=1.0±0.05
α=0.96±0.05
N+Δ→K++Λ+p
π+Λ→K-+N
• 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 KExperimental 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: K0, Λ, Σ(1385), ...
Summary and perspectives
?
RHIC DATA: STAR Collaboration, PRL 97 (2006) 132301
THERM. MOD.: .A. Andronic, NPA 772 (2006) 167
URQMD MOD.: M. Bleicher, NPA 715 (2003) 85
Adams et al., PRC 71 J(2005) 064902
PRELIMINARY
FOPI Al+Al
X. Lopez et al., to be submitted to PRL
K(892) with K+π- in Al+Al @ 1.9 AGeV
K*
K*
BW FIT
FFIT
FFIT  BW  P S
Effect of PS function:
temperature ↔ high Inv. Mass
colder
• Mean Value of Pt = 422 MeV
• "Freeze out temperature": Tfo = 65 MeV
Final parameters (mass, Γ) in agreement
with PDG
BW 
M Kπ ΓM 0
(M2Kπ  M 02 ) 2  M 02 Γ 2
Γ 0 M  (M  M  M )  4M M 


4
M Kπ  (M  M  M )  4M M 

M 2Kπ  Pt2 
M Kπ

PS
 exp 


2
2
Tfo
M Kπ  Pt


Γ
4
0
2
Kπ
2
0
2
π
2
π
2 2
K
2 2
K
2
π
2
π
2
K
2
K
3
2
Measurement of K(892) with FOPI
Al+Al 1.9 AGeV
K*0
(ds)
K++π-
(2/3)
K0+π0 (1/3)
cτ = 4 fm
Eth=2.75 GeV
K++ π-
PDG: Mass = 896 MeV
Γ = 50 MeV
• 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)/K0 yields ratio
• A temperature of 70 MeV does not
reproduce ratio with resonances
P(K*0/K0)
DATA
Therm.
(T=70 MeV)
UrQMD
0.0383±0.0105
0.0225
0.1
PRELIMINARY
Σ(1385) in transport model UrQMD (M. Bleicher-S. Vogel)
Data σgeo ≤315 mb:
P(Σ*-+Σ*+)/(Λ+Σ0)=0.125±0.026(stat.)±0.033(syst)
• Ratio at production time (~10 fm/c)
P(Σ*-+Σ*+)/P(Λ+Σ0) = 0.195
• Ratio with reconstructable Σ* (>200 fm/c)
P(Σ*-+Σ*+)/P(Λ+Σ0) = 0.177
~8% πΣ* 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
K(892) in transport model UrQMD (M. Bleicher-S. Vogel)
Data σgeo ≤315 mb preliminary:
P(K*0)/(K++K0)=0.021±0.005(stat.)±(syst.→P. Velten)
• Ratio at production time (~10 fm)
P(K*0)/P(K++K0) = 0.0803
• Ratio with reconstructable K*0 (>200 fm and in K++π-)
P(K*0)/P(K++K0) = 0.077
~4% πK* lost in inelastic rescattering
• K* creation processes
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
Y. Akaishi et al., PRC 65 (2002)044005
T. Yamazaki et al., PLB (2002) 53570
A. Doté et al., PRC 70 (2004) 044313
• 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
BUT theoretical controversies !
V.K. Magas et al., nucl-th/0601013
E. Oset et al., nucl-th/0509048
K- +d reaction: the search for dibaryons
via Λp correlations (1963-1985)
R.J. Oakes, PR 131 (1963) 2239
R.L. Jaffe, PRL 38 (1977) 195
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/c2.
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-+d→π-+X+ 1.06GeV/c
K-+d→π-+Λ+p
at rest
K-+d→π-+X+ 0.92GeV/c
T.H. Tan, PRL 23 (1969) 395
C. Pigot el al., NPB 249 (1985) 172
K- stopped on 4He, 7Li,
12C
(2005-2006)
T. Yamazaki and Y. Akaishi nucl-exp/0609041
M. Agnello et al.,
PRL 94, (2005) 212303
T. Yamazaki et al.
Prediction of K- bound
state to explain Finuda
results (KeK)
K- stopped in 7Li
Controversies start on
Λ(1405) description
E. Oset et al., attributes
the structure to final
state interaction (FSI)
→ no peak in pp reac.
K- stopped in 12C
Excess in Λp inv.
mass [2.2;2.3]GeV/c2
(Γ=67 MeV)
V.K. Magas, E. Oset nucl-th/0601013
Search for kaonic clusters in heavy ions collisions
A. Andronic et al., NPA 765 (2006) 211
Thermal model predicts a high production yield of antikaonic clusters in heavy ions collisions at SIS energies
Decay channels of
clusters of anti-kaons
accessible with FOPI

Σ*
ppK    p  263 MeV
ppnK    d  208 MeV
pppK    p  p  219 MeV
ppnnK    t  217 MeV
pppnK    3He  219 MeV
SIS
• Excess found at 2.13 GeV/c2
- limit of the significance
- final state interaction (ΣN), dibaryons H1+(2130) ?
- flat distribution in [2.2;2.4] GeV/c2 → no evidence
of the FINUDA structure
Ni+Ni 1.93 AGeV
Λp
• 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
Kaonic clusters in heavy ions collisions
Thermal model predicts a high production yield of antikaonic clusters in heavy ions collisions at SIS energies
A. Andronic et al., NPA 765 (2006) 211
Decay channels of clusters of anti-kaons accessible with FOPI :
ppK    p  263 MeV
ppnK    d  208 MeV
pppK    p  p  219 MeV
ppnnK    t  217 MeV
pppnK    3He  219 MeV
Ni+Ni, 1.93 AGeV
SIS
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)
Where is located the excess
in phase space ?
all
Λp in Ni+Ni:
y0=ycm -1
Enhancement of the signal by
selecting rapidity far off the
mid-rapidity (y0=0)
Excess distribution around the
spectator region: need cold
matter to form Λp clusters ?
y0>-0.35
y0<-0.35
Signal
BKG
Target
cm
Proj.
S-B
KN potential and states
• K- N interaction is
dominated by sub-threshold
resonances ()
K* with K+ (Al+Al @ 1.9 AGeV) DATA
K+
K*
NEVT=290853550
NK+=411941±641
NK*=5792±950
Λ selected for Σ* analysis in Al & Ni data
Al+Al
Ni+Ni
10<TMUL<33
25<TMUL<58
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