Excited QCD Krynica-Zdrój, Feb 5, 2020 News from NA61/SHINE: small and large systems Maciej Lewicki maciej.lewicki@uwr.edu.pl University of Wrocław Institute of Theoretical Physics
Section 1 Studies of the Onset of Deconfinement
Phase Transitions in QCD T (temperature) LHC RHIC QGP SPS 1 s t o r d e r p h a s e t r a n s i t i o n HG µ B (bary on chemical potential) Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 1 / 29
Phase Transitions in QCD T (temperature) c o l l i s i o n Becattini, Manninen, Gaździcki e n e r g Phys. Rev. C 73, 044905 (2006) y system size QGP SPS 1 s t o r d e r p h a s e t r a n s i t i o n HG µ B (bary on chemical potential) Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 1 / 29
Strangeness as a probe of deconfinement No strangeness content in colliding nuclei. Sensitive to the state of matter created in the fireball. confined matter quark-gluon plasma T C ≈ 150 MeV K mesons − → (anti-)strange quarks 2: q , ¯ q g K = 4 g s = 12 Phase transition 2 × spin 3 × color 2 M ≈ 2 · 500 MeV 2 m ≈ 2 · 100 MeV Lightest strangeness carriers: relatively heavy kaons ( M > T C ) in the confined phase, relatively light strange quarks ( m � T C ) in QGP. Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 2 / 29
Main strangeness carriers in A+A collisions at high µ B strangeness conservation ¯ s s = isospin isospin symmetry symmetry ≈ ≈ ¯ K + K 0 K − K 0 ≪ high baryon ≈ density high baryon density ≪ ¯ Λ Λ – sensitive to strangeness content only – sensitive to strangeness content and baryon density p + p → p + Λ + K + + π 0 ≈ [GeV] 0.94 + 0.94 → 0.94 + 1.12 + 0.49 + 0.14 p + p → p + p + K + + K − ≈ [GeV] 0.94 + 0.94 → 0.94 + 0.94 + 0.49 + 0.49 The first option is almost 200MeV "cheaper". Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 3 / 29
Strange definitions Strangeness production � N s ¯ s � – number of s - ¯ s pairs produced in a collision. s � = � Λ + ¯ Λ � + � K + ¯ 2 · � N s ¯ K � + � φ � + . . . multistrange hyperons Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 4 / 29
Strange definitions Strangeness production � N s ¯ s � – number of s - ¯ s pairs produced in a collision. s � = � Λ + ¯ Λ � + � K + ¯ 2 · � N s ¯ K � + � φ � + . . . multistrange hyperons s � ≈ � Λ � + � K + + K − + K 0 + ¯ K 0 � 2 · � N s ¯ ∝ � π � Entropy production The experimental ratio of strangeness to entropy can be defined as: E S = � Λ � + � K + ¯ K � 2 · � N s ¯ s � ≈ � π � � π � � π � ≈ 3 s � ≈ � K + � + � K 0 � 2 · � K + � , � π + � + � π − � � � � N s ¯ ≈ 2 � K + � � K + � � N s ¯ s � ≈ 2 E S ≈ 4 � π + � , � π + � � π � 3 3 Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 4 / 29
Section 2 Theoretical Models
Models of strangeness production There are multiple approaches to describe the strangeness production in HIC. I want to briefly introduce some of them: Statistical Models: ◮ Hadron Resonance Gas ◮ Statistical Hadronization Model ◮ Statistical Model of Early Stage include deconfinement Dynamical Models: explicitly ◮ Rafelski-Müller toy model ◮ Parton-Hadron String Dynamics Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 5 / 29
Hadron Resonance Gas → Assumption of chemical equilibrium. Density of particle species i : p 2 dp ∂ lnZ i n i ( µ, T ) = N i V = − T = g i � , µ i = µ B B i + µ S S i + µ I 3 I 3 , i Ei − µ i V ∂µ 2 π 2 e ± 1 T Chemical potentials µ i constrained by conservation laws: � V n i B i = Z + N → µ B baryon number: i 3 equations, 5 unknowns � n i S i = 0 → µ s strangeness: V ↓ i 2 free parameters n i I 3 , i = Z − N charge: � V → µ I 3 , i 2 i Two free parameters ( T , µ B ) are fitted to experimental data on particle yields. Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 6 / 29
Particle yields – input to HRG model dN/dy N part =350 10 2 10 π + π - 1 – p p K + K - – Λ Λ -1 10 AGS SPS RHIC 2 10 10 √ s NN (GeV) The energy dependence of experimental hadron yields at mid-rapidity for various species produced in central nucleus-nucleus collisions. (Andronic, Braun-Munzinger, Stachel; Nucl.Phys.A772:167-199,2006) Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 7 / 29
Hadron Resonance Gas (Andronic, Braun-Munzinger, Stachel; Nucl.Phys. A834 (2010) 237C-240C) Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 8 / 29
Statistical Hadronization – γ s , γ q Results on strangess in HRG were not satisfactory. Parameter of "phase-space occupancy" γ s introduced to improve the fits: Due to larger mass of s quark it requires more time to saturate and so it doesn’t reach equilibrium value. → γ s < 1 at lower collision energies (AGS, SPS). → γ s = 1 at higher energies (from RHIC). Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 9 / 29
Statistical Hadronization – γ s , γ q Results on strangess in HRG were not satisfactory. Parameter of "phase-space occupancy" γ s introduced to improve the fits: Due to larger mass of s quark it requires more time to saturate and so it doesn’t reach equilibrium value. → γ s < 1 at lower collision energies (AGS, SPS). → γ s = 1 at higher energies (from RHIC). Later on γ q was introduced to tune the fits for u , d quarks. Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 9 / 29
Statistical Hadronization – γ s , γ q dotted: γ q , γ s = 1 dashed: γ q = 1 , γ s < 1 but is it still a statistical model? solid: γ q , γ s < 1 (J. Rafelski; Eur.Phys.J.ST 155 (2008) 139-166) Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 10 / 29
Strangeness in Statistical Model of Early Stage � MT � 3 / 2 e − M / T ≈ gV � gV 1 for heavy particles 2 π d 3 p � n � = e E / T ± 1 ( 2 π ) 3 gV 2 π 2 4 · 45 T 3 ≈ for light particles > non-strange < < N ss > / - T MT 3 / 2 � u + d + g � ∝ T 3 � K � � s � · e − M / T ∝ T 3 = const ( T ) � π � T 3 Gaździcki, Gorenstein, Acta Phys.Polon. B30 (1999) 2705 Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 11 / 29
Strangeness in Statistical Model of Early Stage Strange/non-strange Temperature dependence on collision energy in SMES : particle ratio: > T[MeV] 300 non-strange 250 QGP 200 < 150 < N ss > / - 100 0 5 10 15 20 25 s NN [GeV] s NN Crossing the phase transition leads to a decrease of the strange/non-strange particle ratio – the horn-like structure – Mareks’ horn. Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 12 / 29
Dynamical Approach by Rafelski-Müller strangeness production in confined matter strangeness production in QGP N + N → N + Y + K q 1 k 1 π + N → K + Y k π + N → K + Y 2 -q 2 π + Y → Ξ + K π + Y → Ξ + K k 1 q 1 k π + Ξ → Ω + K -q π + Ξ → Ω + K 2 2 1 fm/ c 100 fm/ c (Rafelski, Müller, Phys. Rev. Lett. 48 (1982) 1066) Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 13 / 29
Rafelski-Müller Dynamical Approach > non-strange QGP < < N ss > / - s NN Equilibrium value reached in QGP ← fast strangeness production. No enhancement in the confined phase ← slow strangeness production in whole hadronic region. Deconfinement happens in the collisions of heavy ions, but not in p+p interactions. → explanation for system size dependence ( A+A vs p+p ). Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 14 / 29
PHSD model with & without C hiral S ymmetry R estoration in the confined phase Implements the onset of deconfinement. Without CSR – prediction of PHSD qualitatively resembles predictions of the Rafelski-Müller model. With CSR – enhanced strangeness production in the confined phase. The strange quark mass used in the string decay Schwinger-formula in assumed to decrease with energy density, while still in the confined phase. (Palmese et al. , PRC94 (2016) 044912) Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 15 / 29
Collision energy dependence of strangeness production "horn" plot SMES 0) Pb+Pb Au+Au > ≈ (y LHC non-strange AGS + SPS NA49 π / RHIC + K 0.2 QGP < < N ss > / 0.1 - 0 2 4 10 10 s NN 1 s [GeV] NN Qualitatively, heavy-ion data follows dependence predicted by SMES . Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 16 / 29
Before NA61/SHINE No precise baseline of p+p collisions. No data on system size dependence of particle production at SPS energies – vicinity of the onset of deconfinement. Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 17 / 29
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