Global dynamics and strangeness production in HI 1-2A GeV with FOPI

Transcription

1 Global dynamics and strangeness production in HI 1-2A GeV with FOPI Institute of Experimental Physics, Faculty of Physics, University of Warsaw, Poland Global dynamics of HI collisions: Stopping, Flow, Yield ratios, Phase diagram Strangeness production In-medium modifications of K+,-,0 Other sources of K- : Σ(1385), φ Neutral strangeness

2 Heavy Ion Collisions around Ebeam = 1-2A GeV Dynamical picture Phase diagram Dense Baryonic Medium ρb 2..3 ρ0 π± K±0 φ Λ Σ0 K* Σ*± τ ~ fm/c TFreeze Out = MeV Equilibration at freeze-out? Dynamical picture vs 2-dim phase diagram? 2

3 FOPI experimental setup Magnet CDC RPC Zero Degree Nearly 4π coverage Drift chambers: chambers CDC, Helitron ToF : Plastic Barrel, RPC Forward: Forward Plastic Wall, Zero Degree Beam Plastic Barrel Helitron Plastic Wall NIPNE Bucharest, Romania ITEP Moscow, Russia CRIP/KFKI Budapest, Hungary LPC Clermont-Ferrand, France Korea University, Seoul, Korea IMP Lanzhou, China Kurchatov Institute Moscow, Russia ITEP Moscow, Russia TUM, Munich, Germany SMI Vienna, Austria GSI Darmstadt, Germany IReS Strasbourg, France FZ Rossendorf, Germany Univ. of Heidelberg, Germany Univ. of Warsaw, Poland RBI Zagreb, Croatia 3

4 Identificaton of charged particles Tracks in CDC log (de/dx) (a.u.) CDC d π- π+ 1.5A GeV p/q (GeV/c/e) Direct identification of π±, K±, p, d, t, Barrel p (GeV/c) t p d p He 3,4 RPC t d p K π K+ π+ v (cm/ns) 4

5 1. Global dynamics Nuclear stopping vs transparency Directed flow of charged barions Elliptic flow of charged barions 5

6 Rapidity distributions All charged baryons: p,d,t,3,4he,li,... protons, deuterons 1.93A GeV Variance t/l ratio: 2 vartl = 2 yz W.Reisdorf et al., PRL 92, (2004) (schematic) yt FOPI Central y 0z B.Hong et al (FOPI), PRC 57, 244 (1998) Initial state: Transparency Final state: stopped Reasons: transparent Partial transparency Low Tbeam Pauli exclusion High Tbeam in-medium σ (?)

7 Side flow p xdir = sgn y Zv x 0 Pattern identical as vartl! max (pxdir) max 1 v beam 1 Z

8 Elliptic flow Correlation between dn 1 2v 1 cos 2v 2 cos 2... d Au+Au more stopping (vartl) more pressure more side flow (pxdir) more shadowing in-plane more out-of-plane emission (v2) more transparency (vartl) less pressure less side flow (pxdir) less shadowing in-plane less out-of-plane emission (v2) FOPI peripher. intermed. central A.Andronic et al., Phys.Lett B 612, 173 (2005) vartl and max[ pxdir ]

9 2. Strangeness in medium KN interaction (potential) Directed flow K momenta of π+a and p+a K-/K+ as function of Kinetic Energy and Rapidity Other K- sources Σ±* (1385), φ

10 Sub- and Nearthreshold Production of Kaons Production thresholds: NN NK+Λ Elab= 1.6 GeV At SIS energies, resonance production NN K+K NN Elab= 2.5 GeV (Δ, N*) reaches maximum P.Senger et al. (KAOS), F. Laue et al., PRL 82 (1999), updated S.A. Bass et al., PPNP 41 (1998) 225 FOPI Production processes (dominant) K+0 and Y via multi-step processes K production more complex : N+N Δ+N K+,0 + Y + B via strangeness exchange reactions : coupled to resonances e.g. Σ(1385), (1385) Λ(1405) and Λ(1520) K N potential attractive π + Y K + B

11 Probing partial restoration of chiral symmetry Gell-Mann Oakes Renner relation: m 2 K f 2 K = m u m s 2 u u s s m2s Decay constant Mass W. Weise, Prog.Theor.Phys.Suppl. 149, 1 (2003) Energy of Kaon in medium: K = p 2 K U(K+) 2 m U S U V K- For p = 0, K = m V Total U = F K- attracted K+ repelled Ways to probe U(K) : Sideward Flow of kaons K-/K+ vs kinetic energy U(K-) J. Schaffner-Bielich et al. NPA 625(1997) 325 FOPI Decay constants Kaonic clusters 11

12 In-medium KN potential: K+ Flow dn 1 2v 1 cos 2v 2 cos 2... d P. Crochet et al. (FOPI), PLB 486, 6 (2000) 1.93A GeV 1.69A GeV central -1.2 <y0< <y0< K+ flow compared to RBUU, favours weak repulsive U(K+N) ~ +20 MeV 12

13 In-medium KN potential at ρ < ρ0 γ, π, p Beam π (p=1.15 GeV/c) + A K0 + SIS 18 H.I. Coll. W. Weise, Prog.Theor.Phys.Suppl. 149, 1 (2003) p (p=2.25 GeV/c) + A K+ + FOPI ANKE VKN = 0 MeV VKN = 10 MeV VKN = 20 MeV CBUU ANKE p + A K+ + pp = 2.25 GeV/c M.L. Benabderrahmane et al., PRL 102, (2009) Z. Rudy et al., EPJA 23, 379 (2005) 13

14 In-medium KN potential: K-/K+ yield Data vs RBUU RBUU U=0 K-/K+ flat Strong effect at low Ekin kin 150 < Θcm < 165 K. Wiśniewski et al. (FOPI), EPJ A9, 515(2000) E cm [GeV ] Data vs RBUU Clear preference for UKN > 0 option Red/Blue = Soft/Hard EOS option Still description not ideal 14

15 K- and K+ data from KaoS Our understanding too simplistic? K- production via resonances Some K- from φ (outside medium) 15

16 K- production in medium Chiral perturbation theory (χpt) K- spectral density [GeV-2] Antikaon spectral function in dense matter M.F.M. Lutz, PPNP 53, 125 (2004) Strange resonances in K- production Σ(1385) mn+mk FOPI 1.93A GeV Λπ- + Λπ+ Σ±* (1385) Λ + π± (88 ± 2%) p+π Eth = 2.33 GeV Γ = 39.4 MeV, cτ = 5 fm (subthreshold) (short lived) P = 0.125±0.026±0.033 P 0 X. Lopez et al. (FOPI), PRC 76, (R) (2007) 16

17 φ meson (ss) φ (ss) K+K- (BR = 49%) m = 1019 MeV cτ = 50 fm Eth = 2.6 GeV (decays mostly outside collision zone) (subthreshold) 1.93A GeV (P. Gasik) 1.93A GeV preliminary (KP) preliminary minv [GeV/c2] Pφ / collision = (2.2±0.5±0.2) 10-4 Pφ / collision = (6 ± 1 ± 2) 10-4 P P K - P P K - = 0.27±0.10 = 0.44±

18 3. The Final Concerto Strange neutral particles: K0 and Λ0 Kinematical temperature Statistical temperature Phase Diagram 18

19 K0 and Λ at 1.9A GeV K0 and Λ (from secondary vertices) K0 π+ + π Λ π + p Ni+Ni Al+Al (69%) (64%) Identification of K0 and Λ K0 d s 30 k 60 k Λ uds 60 k 100 k Phase space: occupancy vs acceptance 1.93A MeV M. Merschmeyer, X. Lopez et al. (FOPI), PRC 76, (2007) 19

20 K0 and Λ: phase space analysis M. Merschmeyer, X. Lopez et al. (FOPI), PRC 76, (2007) K0 Ebeam = 1.93A GeV Ni+Ni Λ K0 Λ and K0 obeying Boltzmann distributions Λ Λ and proton: emission patterns different (p transparency) Temperature of colliding system 2 T eff 2 m 0 rad = T 3 2 Ni+Ni: radial flow Al+Al: almost no expansion Same kinetical freeze-out T in Al+Al and Ni+Ni (T ~ MeV) 20

21 Statistical model: particle yields Yield SPS Assumption: Assumption chemical freeze-out A.Andronic, P.Braun-Munzinger, J.Stachel NPA 772 (2006) 167 Density of species i (in grandcanonical ensemble) : Ni gi n i,t = = V p 2 dp E i B Bi S S i I I 3i exp ±1 T 3 Pb+Pb Free parameters: chemical potential µb temperature T For particle ratios : V cancels out Fixed by conservation laws: µs, µι3 looks promising 21

22 Particle yields at freeze-out Al+Al 6 independent ratios with 5 strange particles : p, π, K0, Λ, φ, K*0(892) and Σ*±(1385) Ni+Ni 8 independent ratios with 4 strange particles 1.93A MeV prelim. p,d, π±, K±, K0, φ, Λ FOPI/KAOS (calc.: THERMUS code S.Wheaton, J.Cleymans hep-ph/ ) Grand Canonical ensemble; For S 0, Canonical ensemble 1.93A MeV Ni+Ni prelim. Statistical Model T ~ 70 MeV, µb = 770 MeV For Al+Al, γs 1 Model fitting well 22

23 Freeze-out on phase diagram P.Braun-Munzinger, J. Wambach, Rev. Mod. Phys 81, 1031 (2009) T ~ MeV RHIC SPS from mt spectra (kinematic freeze-out) AGS T ~ 70 MeV from Statistical Model (chemical freeze out) Assumming those models, we obtain Tkin > Tchem... Is the equilibrium assumption wrong? Need for more systematics 23

24 Particle yields and UrQMD 1.93A GeV UrQMD M.Bleicher, S.Vogel Uni Frankfurt No equilibration assumed Cascade model no mean field prelim. no in-medium effects Σ*± and K* reconstructable in experiment: Excluded decay products undergoing inelastic rescattering with medium UrQMD in agreement with data and Statistical Model Either: More precise data needed Or: Integrated yields are not a good signature to study thermalisation issues 24

25 Summary and conclusion General dynamics of the collision at 1-2A GeV: stopping pressure side flow shadowing out-of-plane preference vartl max [pxdir] v2 In-medium modification of strangeness Flow of K+ pkaon (Pb) / pkaon (C) K+/K- (Ekin) K+ and K- separately VKN +20 MeV VKN +20 MeV VKN +30 MeV, VKN -70 MeV (quantitative) with in-medium better, but inconclusive Other kaon sources [ Σ*(1385), φ ] may bias model calculations of in-medium effects Phase space analysis of particles kinematical temperatures Tkine Yield ratio compared to thermal model thermal temperatures Tther Unexpected inversion Tkine > Tther thermal assumption wrong? 25

26 Thank you 26