Strange meson production near threshold Strange meson production - PowerPoint PPT Presentation

Strange meson production near threshold Strange meson production near threshold FOPI FOPI in nucleus-nucleus collisions in nucleus-nucleus collisions Krzysztof Piasecki for the FOPI Collaboration Institute of Experimental Physics, University of Warsaw, Poland • Physics motivation • • Primary or secondary production? • • K – production: a complex case • • In-medium modifications of K +, – , 0 • • K * (892) strange meson resonance • • Summary and conclusions • 1 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

Strange mesons in AA collisions Strange mesons in AA collisions NN → N K +/ ° Λ T lab = 1.6 GeV • Production thresholds • NN → NN K – K + T lab = 2.5 GeV in free NN collision : NN → NN φ T lab = 2.6 GeV G. Agakishiev, Phys Rev C 80, 025209 (2009) P. Gasik, Ph. D. Thesis, University of Warsaw Al+Al @ 1.93 GeV F. Laue et al. , PRL 82 (1999), updated φ P.Senger et al. (KAOS), φ Ar+KCl @ 1.76 GeV HADES KaoS They a r e here . . . • Strange mesons in AA collisions Strange mesons in AA collisions: : • – Are the production processes primary or secondary? – Decays? Contributions from intermediate resonances? – Modification of properties in medium? – Production of strange resonances? 2 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

Probing partial restoration of chiral symmetry Probing partial restoration of chiral symmetry Gell-Mann O Oakes R Renner – relation : G m u + m s FOPI AA ∗ 2 f K ∗ 2 = − s s 〉 + Θ ( m s 2 ) m K 〈̄ uu +̄ 2 Decay constant Mass M. Kotulla et al., Physik Journal 8 (2009) 3 • First approaches: Potential • • Chiral effective field theory w/ couple-channels • J. Schaffner-Bielich et al . NPA 625(1997) 325 U(K + ) M.F. M. Lutz, PPNP 53 (2004) 125 K + U(K - ) K – F =− ⃗ • ⇒ K - attracted, K + repelled ⃗ • „Potential” only on average ∇ U 3 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

FOPI experimental setup FOPI experimental setup Nearly 4 π coverage Drift chambers Drift chambers: CDC, Helitron ToF ToF : Plastic Barrel, RPC Forward Forward: Plastic Wall, Zero Degree Direct PID of π ± , K ± , p, d, t, 3,4 He MMRPC t t d d p p + Plastic Barrel K + K p / |q| [GeV/c] π + + π + e + e t t d d - e - p [GeV/c] e p p π - - π - K - K + K + K π + π v (cm/ns) v (cm/ns) 4 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

Production of Kaons in AA: Primary or secondary? Production of Kaons in AA: Primary or secondary? If primary: σ K MUL K = σ inelastic = const For pA → KX: M.Merschmeyer et al., PRC 76, 024906 (2007) AA→ KX: Glauber: AA = A ⊗ NA FOPI FOPI AA = A × MUL K pA ∝ A ⇒ MUL K Ni+Ni, 1.9A GeV KaoS A. Förster et al., PRC 75, 024906 (2007) K 0 : secondary processes involved K +0 +0 near-threshold production processes: near-threshold production processes: K • N beam + N target , N target has Fermi motion • • predominantly via ΔN , ΔΔ • ΔN , ΔΔ → K → K +,0 Y B +,0 Y B π N , π Δ π N , π Δ → K → K +,0 +,0 Y Y Y = [ Λ , Σ ] • • A U U KN involved (increases K mass → lower yields) → lower yields) KN involved (increases K mass secondary processes are involved secondary processes are involved 5 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

Sub- and near-threshold Production of K – Sub- and near-threshold Production of K – • in medium: mainly strangeness exchange : • Au+Au, T b = 1.5A GeV (IQMD IQMD transport code) π Y → , π Y → – B BY → NNK BY → NNK – K K – B – , π Y ◦ ◦ strong reabsorption: K K – B → π Y – B → ◦ ◦ coupled to resonances Σ Σ(1385) (1385), Λ Λ(1405) (1405) Σ* Σ* π π + Y → → + Y → → – + B K K – + B Λ* Λ* Q: Can we see them? K − • φ (1020) → K – K + decay (mostly outside collision zone) • Q: How strong is this contribution? • I n-medium effects: “U KN • potential” or “spectral density” φ Q: How strong is this influence? t (fm/c) K − K + 6 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

φ φ (1020) mesons mesons (1020) • φ (ss) → K + K – (BR = 49%) • Ar+KCl, T b = 1.76A GeV m = 1019 MeV HADES c τ = 50 fm ( decays mostly outside collision zone ) S = 168 E th = 2.6 GeV ( for SIS-18, deeply subthreshold) φ / K – Al+Al, T b = 1.9A GeV S = 108 (FOPI) S/B = 1.0 (FOPI) (FOPI) (FOPI) (FOPI) Signif = 7.4 Ni+Ni, T b = 1.9A GeV (FOPI) S = 170 S/B = 0.7 Signif = 8.4 • P φ possibly ~ <A part > • preliminary φ - ≈ 1 ~ 15 .. 20% of K -- ~ 15 .. 20% of K -- • • 3 φ decays K produced from φ produced from decays G. Agakishiev, Phys Rev C 80, 025209 (2009) P. Gasik, Ph. D. Thesis, University of Warsaw 7 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

φ /K φ /K – excitation function – excitation function G. Agakishiev et al., PRC 80, 025209 (2009) p + p J. Cleymans et al. PLB 603, 146 (2004) within S S tatistical M M odel • For S≠0, Canonical ensemble • • φ : non-strange , K – : strange • • At low √ s , φ /K – sensitive to R Canonical FOPI • R Canonical ~ 2-3 fm φ phase space Exploring φ phase space Exploring Ni+Ni @ 1.9A GeV Ar+KCl @ 1.76A GeV Al+Al @ 1.9A GeV T eff = 84 ± 8 MeV T eff = 91 ± 20 MeV T = 92 ± 12 MeV HADES preliminary 95°< ϑ CM <150° preliminary 8 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

Σ ∗ Σ ∗ (1385) resonance (1385) resonance • Al+Al, T beam = 1.9A GeV • Chiral effective field theory w/ coupled-channels Chiral effective field theory w/ coupled-channels Σ ±* (1385) → Λ + π ± (88 ± 2%) K – production in medium ( π Y → K – N ) coupled • • p + π – ↳ to strange resonances e.g. Σ ∗ (1385), Λ ∗ (1405) : X. Lopez et al. (FOPI), PRC 76, 052203(R) (2007) ( πΛ → Σ ∗ → K – N ) Λπ - + Λπ + M.F. M. Lutz, PPNP 53 (2004) 125 Σ ∗ (1385) m N +m K Y (Σ ∗ − +Σ ∗+ ) Y (Λ+Σ 0 ) FOPI 0.125 ± 0.042 Σ * resonance found in HI collisions • • Statist. Model 0.097 Input to fix π + Λ → K – + N in medium UrQMD 0.177 9 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

K – /K + : experiment vs transport K – /K + : experiment vs transport Al+Al, T beam = 1.9A GeV, 9% most central events • K + : U KN repulsive • (P. Gasik) K – : U KN ~attractive K – /K + : promising observable • IQMD • IQMD transport code m K ± (ρ) = m K ± (ρ 0 ) ⋅ ( 1 +α ± ⋅ρ ρ 0 ) ◦ ◦ ◦ at ρ = ρ 0 ◦ preliminary ∆ m K+ = 40 MeV, ∆ m K- = ‒ 100 MeV 136° < Θ cm < 150° • HSD • HSD transport code ◦ K + as in IQMD ◦ HSD, U K+N =40 MeV, K- Not Modified IQMD, NO Pot. ◦ K – : off-shell G-matrix approach ◦ HSD, U K+N =40 MeV, U K-N = G-Matrix HSD , NO Pot. IQMD, U K+N =40 MeV, U K-N =-100 MeV • • Clear preference for U KN ≠ 0 option • ”U K+ only” scenario : insufficient • • IQMD: potentials used probably too strong • 10 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

Flow of charged kaons Flow of charged kaons directed flow v 1 dN d   1  2v 1 cos   2v 2 cos  2   ... v 1 v 1 , v v 2 2 = Fourier coefficients Ni+Ni , T beam = 1.9A GeV 40% central V. Zinyuk et al, arXiv: 1403.1504v2 K – K + p more preliminary 11% central peripheral : U K+N = 20 MeV U K-N ≈ -50 MeV HSD HSD ~ In favour of the potential IQMD IQMD : U K+N = 20 MeV U K-N = -40 MeV 11 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

ρ < ρ 0 at ρ < ρ In-medium modifications of K +/0 In-medium modifications of K +/0 at 0 γ, π , p Beam π – (p=1.15 GeV/c) + A → K 0 + … FOPI p (p=2.25 GeV/c) + A → K + + … ANKE M. Kotulla et al., Physik Journal 8 (2009) 3 M.L. Benabderrahmane et al., PRL 102, 182501 (2009) M. Nekipelov et al, PLB 540, 207 (2002) p = 1.15 ANKE p + A → K + + … Z. Rudy et al., EPJA 23, 379 (2005) p = 3.1 p p = 2.25 GeV/c U KN = 0 MeV CBUU CBUU U KN = 10 MeV transport code U KN = 20 MeV 12 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014

Modifications of K 0 in AA collisions AA collisions Modifications of K 0 in 0 K S 0 c τ = 2.7 cm from Ar + KCl @ 1.76A GeV K S c τ = 15.3 m 0 K L IQMD transport calc. : IQMD No potential U K0N = 46 MeV HADES U KN at ρ ~ 2 ρ 0 seems to be stronger than for π – A → K 0 + … at ρ ≤ ρ 0 G. Agakichiev et al., Phys. Rev. C 82, 044907 (2010) 13 K. Piasecki (FOPI) 13 th Intl. Workshop on Meson Production, Properties and Interaction 2.06.2014