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

21

fm

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 23

232 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 39.4c (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 assumptionsNeed 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

Conclusion / Outlook

• Measurement of resonances in Ni+Pb s½ = 2.7 GeV - highest beam kinetic energy / projectile mass

- enhancement of the number of nucleons in the target

- best compromise between s½ 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 (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)

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 V2 for K+ and K- show in-medium effect• The trend of V2 for K+ and K- is different compared to the models

Elliptic flow of Kaons

A. Mishra et al. PRC 70(2004) 044904

in plane

out of plane

Y-J. Kim, to be submitted to PRL

KAOS data: F. Uhlig et al. PRL 95(2005) 0123101

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- productionStrangeness 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) 152301

1.5 AGeV

Strangeness exchange reactions

A. Förster et al., nu/ex 0701014

• 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: K0, Λ, Σ(1385), ...

α=1.25±0.12α=1.22±0.27

α=1.26±0.06α=1.34±0.16

α=1.0±0.05α=0.96±0.05

αpartA~M

N+Δ→K++Λ+pπ+Λ→K-+N

Summary and perspectives

Adams et al., PRC 71 J(2005) 064902

FOPI Al+Al PRE

LIM

INA

RY

?

RHIC DATA: STAR Collaboration, PRL 97 (2006) 132301

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 Al+Al @ 1.9 AGeV

K* K*

BW FIT

Adams et al., PRC 71 J(2005) 064902

fo

2t

2Kπ

2t

2Kπ

Kπ

23

2K

2π

22K

2π

20

2K

2π

22K

2π

2Kπ

4Kπ

400

220

220

2Kπ

0Kπ

FIT

TPM

expPM

MPS

M4M)MM(MM4M)MM(M

MMΓ

Γ

ΓM)M(MΓMM

BW

PSBWF

FFIT

Effect of PS function: colder temperature ↔ high Inv. Mass

• Mean Value of Pt = 422 MeV

• "Freeze out temperature": Tfo = 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)/K0 yields ratio

• A temperature of 70 MeV does not reproduce ratio with resonances

K*0 K++π- (2/3)

K0+π0 (1/3))s(d

cτ = 4 fm Eth=2.75 GeV

PDG: Mass = 896 MeV

Γ = 50 MeV

K++ π-

Al+Al 1.9 AGeV

DATA Therm. (T=70 MeV)

UrQMD

P(K*0/K0) 0.0383±0.0105 0.0225 0.1

PRELIMINARY

Σ(1385) in transport model UrQMD (M. Bleicher-S. Vogel)

• 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

Data σgeo ≤315 mb:

P(Σ*-+Σ*+)/(Λ+Σ0)=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++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

Data σgeo ≤315 mb preliminary:

P(K*0)/(K++K0)=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)044005 T. Yamazaki et al., PLB (2002) 53570 A. Doté et al., PRC 70 (2004) 044313

V.K. Magas et al., nucl-th/0601013E. Oset et al., nucl-th/0509048BUT theoretical controversies !

K-+d→π-+Λ+p

at rest

T.H. Tan, PRL 23 (1969) 395

K- +d reaction: the search for dibaryonsvia Λp correlations (1963-1985)

C. Pigot el al., NPB 249 (1985) 172

R.J. Oakes, PR 131 (1963) 2239 R.L. Jaffe, PRL 38 (1977) 195

K-+d→π-+X+ 1.06GeV/c

K-+d→π-+X+ 0.92GeV/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/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- stopped in 12C

M. Agnello et al., PRL 94, (2005) 212303

V.K. Magas, E. Oset nucl-th/0601013

T. Yamazaki and Y. Akaishi nucl-exp/0609041

E. Oset et al., attributes the structure to final state interaction (FSI) → no peak in pp reac.

K- stopped on 4He, 7Li, 12C (2005-2006)

T. Yamazaki et al. Prediction of K- bound state to explain Finuda results (KeK)

Excess in Λp inv. mass [2.2;2.3]GeV/c2

(Γ=67 MeV)

Controversies start on Λ(1405) description

K- stopped in 7Li

A. Andronic et al., NPA 765 (2006) 211

SIS

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

MeV219

MeV217

MeV219

MeV208

MeV263

3

HepppnK

tppnnK

pppppK

dppnK

pppK

Decay channels of clusters of anti-kaons accessible with FOPI

• 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

• 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

Λp

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

MeV219

MeV217

MeV219

MeV208

MeV263

3

HepppnK

tppnnK

pppppK

dppnK

pppK

Decay channels of clusters of anti-kaons accessible with FOPI :

Excess found on Λd analysis, but cluster mass range unknownNeed 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

PRELIMIN

ARY

Ni+Ni, 1.93 AGeV

Excess distribution around the spectator region: need cold

matter to form Λp clusters ?

Where is located the excessin phase space ?

Λp in Ni+Ni:

y0<-0.35ally0>-0.35

y0=ycm -1

S-BSignal

BKG

Target cm Proj.

Enhancement of the signal by selecting rapidity far off the mid-rapidity (y0=0)

• K- N interaction is dominated by sub-threshold resonances ()

KN potential and states

K* with K+ (Al+Al @ 1.9 AGeV) DATA

K+K*

NEVT=290853550

NK+=411941±641

NK*=5792±950

Al+Al Ni+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