small and large systems Maciej Lewicki maciej.lewicki@uwr.edu.pl - - PowerPoint PPT Presentation

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 µB

(baryon chemical potential) (temperature) 1 s t

• r

d e r p h a s e t r a n s i t i

• n

QGP HG

LHC RHIC SPS

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 1 / 29

Phase Transitions in QCD

T µB

(baryon chemical potential) (temperature) 1 s t

• r

d e r p h a s e t r a n s i t i

• n

QGP HG

c

• l

l i s i

• n

e n e r g y system size

SPS

Becattini, Manninen, Gaździcki

• Phys. Rev. C 73, 044905 (2006)

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 K mesons (anti-)strange quarks gK = 4 gs = 12 2M ≈ 2 · 500 MeV 2m ≈ 2 · 100 MeV

TC ≈ 150 MeV

− →

Phase transition

2: q, ¯ q 2×spin 3×color

Lightest strangeness carriers: relatively heavy kaons (M > TC) in the confined phase, relatively light strange quarks (m TC) 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 µB

¯ s

strangeness conservation

=

s K +

isospin symmetry

≈

K 0

≪

high baryon density

¯ Λ

≪

high baryon density

K −

isospin symmetry

≈

¯ K 0

≈

Λ

– sensitive to strangeness content only – sensitive to strangeness content and baryon density p + p → p + Λ + K + + π0 ≈[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 Ns¯

s – number of s-¯

s pairs produced in a collision. 2 · Ns¯

s = Λ + ¯

Λ + K + ¯ K + φ + . . .

multistrange hyperons

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 4 / 29

Strange definitions

Strangeness production Ns¯

s – number of s-¯

s pairs produced in a collision. 2 · Ns¯

s = Λ + ¯

Λ + K + ¯ K + φ + . . . 2 · Ns¯

s ≈ Λ + K + + K − + K 0 + ¯

K 0 Entropy production ∝ π The experimental ratio of strangeness to entropy can be defined as: ES = Λ + K + ¯ K π ≈ 2 · Ns¯

s

π Ns¯

s ≈ K + + K 0

≈ 2 · K +, π ≈ 3 2

• π+ + π−
• Ns¯

s

π ≈ 2 3 K + π+ , ES ≈ 4 3 K + π+

multistrange hyperons

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

Dynamical Models:

◮ Rafelski-Müller toy model ◮ Parton-Hadron String Dynamics

explicitly include deconfinement

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: ni(µ, T) = Ni V = −T V ∂lnZi ∂µ = gi 2π2

• p2dp

e

Ei −µi T

± 1 , µi = µBBi + µSSi + µI3I3,i Chemical potentials µi constrained by conservation laws: baryon number: strangeness: charge: V

• i

niBi = Z + N → µB V

• i

niSi = 0 → µs V

• i

niI3,i = Z − N 2 → µI3,i 3 equations, 5 unknowns ↓ 2 free parameters Two free parameters (T, µB) 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

10

• 1

1 10 10 2 10 10

2

√sNN (GeV) dN/dy Npart=350

AGS SPS RHIC π+ π- p p

–

K+ K- Λ Λ

–

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 – γs, γq

Results on strangess in HRG were not satisfactory. Parameter of "phase-space occupancy" γs 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. → γs < 1 at lower collision energies (AGS, SPS). → γs = 1 at higher energies (from RHIC).

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 9 / 29

Statistical Hadronization – γs, γq

Results on strangess in HRG were not satisfactory. Parameter of "phase-space occupancy" γs 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. → γs < 1 at lower collision energies (AGS, SPS). → γs = 1 at higher energies (from RHIC). Later on γq 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 – γs, γq

dotted: γq, γs = 1 dashed: γq = 1, γs < 1 but is it still a statistical model? solid: γq, γs < 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

n = gV (2π)3

• d3p

1 eE/T ± 1 ≈ gV MT

2π

3/2 e−M/T ≈ gV 2π2

4·45T 3

for heavy particles for light particles K π ∝ MT 3/2 T 3 ·e−M/T

T <Nss>/

non-strange

• <

>

s u + d + g ∝ T 3 T 3 = const(T)

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

Temperature dependence

• n collision energy in SMES:

sNN [GeV]

5 10 15 20 25 100 150 200 250 300

T[MeV]

Strange/non-strange particle ratio:

sNN

QGP <Nss>/

non-strange

• <

>

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

N + N → N + Y + K π + N → K + Y π + Y → Ξ + K π + Ξ → Ω + K π + N → K + Y π + Y → Ξ + K π + Ξ → Ω + K

strangeness production in QGP

q1

2

k k1

2

• q

2

• q

2

k k1 q1

(Rafelski, Müller, Phys. Rev. Lett. 48 (1982) 1066)

100 fm/c 1 fm/c

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 13 / 29

Rafelski-Müller Dynamical Approach

QGP <Nss>/

non-strange

• <

>

sNN

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 Chiral Symmetry Restoration

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

[GeV]

NN

s 1

2

10

4

10 0) ≈ (y

+

π /

+

K 0.1 0.2

AGS SPS NA49 RHIC

Pb+Pb Au+Au

LHC

SMES

sNN

QGP <Nss>/

non-strange

• <

> 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

NA61/SHINE 2D scan

System size p+p p+Pb Be+Be Ar+Sc Xe+La Pb+Pb Pb+Pb 2009/10/11 2012/14/16/17 2011/12/13 2015 2017 2016/18 2021-24 13 20 30 40 75 150 Beam momentum [A GeV/c]

T µB

(baryon chemical potential) (temperature) 1 s t

• r

d e r p h a s e t r a n s i t i

• n

QGP HG

c

• l

l i s i

• n

e n e r g y system size

SPS

Unique, two-dimensional scan in collision energy and nuclear mass number

• f colliding nuclei.

Unique range in the phase diagram of strongly interacting matter.

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 18 / 29

Ar+Sc: K + spectra in y and pT

10% most central events recorded for Ar+Sc interactions. Traits of fixed target experiments: Acceptance in rapidity covering whole forward hemisphere. Acceptance in pT down to 0.0 GeV/c

(P. Podlaski [for NA61/SHINE Collaboration], SQM Bari 2019, sqm2019.ba.infn.it/)

NA61/SHINE Preliminary

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 20 / 29

Ar+Sc: pT spectra at mid-rapidity

Ar+Sc → K + + X Ar+Sc → K − + X

[GeV/c]

T

p 0.5 1 1.5 dy

T

dp dn 1 2 3 4 5 6

150A GeV/c 75A GeV/c 40A GeV/c 30A GeV/c 19A GeV/c

[GeV/c]

T

p 0.5 1 1.5 dy

T

dp dn 0.5 1 1.5 2 2.5 3 3.5 4

150A GeV/c 75A GeV/c 40A GeV/c 30A GeV/c 19A GeV/c

Spectra fitted with exponential function: 1 pT dn2 dpT dy = dn/dy T · (mK + T) · e−(mT −mK )/T

(P. Podlaski [for NA61/SHINE Collaboration], SQM Bari 2019, sqm2019.ba.infn.it/)

NA61/SHINE Preliminary

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 21 / 29

System size dependence of inverse slope parameter

Ar+Sc → K + + X Ar+Sc → K − + X

1

2

10

4

10 [GeV]

NN

s 200 400 T [MeV]

NA61/SHINE p+p Be+Be Ar+Sc World p+p Pb+Pb/Au+Au

1

2

10

4

10 [GeV]

NN

s 200 400 T [MeV]

NA61/SHINE p+p Be+Be Ar+Sc World p+p Pb+Pb/Au+Au

Ar+Sc in between light and heavy systems. Be+Be very close to p+p. Sensitive to both: thermal and collective motion in the transverse direction. Transverse flow modifies the Boltzmann pT-spectrum of hadrons. Kaons only weakly affected by re-scattering and resonance decays during the post-hydrodynamic hadron cascade at SPS and RHIC energies. Reflects temperature of the freeze-out surface and not the early-stage fireball.

NA61/SHINE Preliminary

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 22 / 29

Ar+Sc: y spectra

1 2

y

2 4

dn/dy

c GeV/ A 150 c GeV/ A 75 c GeV/ A 40 c GeV/ A 30 c GeV/ A 19

+X

+

K → Ar+Sc

1 2

y

1 2 3

dn/dy

c GeV/ A 150 c GeV/ A 75 c GeV/ A 40 c GeV/ A 30 c GeV/ A 19

+X

• K

→ Ar+Sc

Spectra fitted with a sum of symmetric Gaussians: ffit(y) = A ×

• 1

σ0 √ 2π exp

• −(y − y0)2

2σ2

• +

1 σ0 √ 2π exp

• −(y + y0)2

2σ2

• NA61/SHINE Preliminary

NA61/SHINE Preliminary

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 23 / 29

System size dependence of strangeness production

1 10

2

10 [GeV]

NN

s 0.2

〉

+

π 〈 〉

+

K 〈

NA61/SHINE p+p Be+Be Ar+Sc World p+p Pb+Pb/Au+Au SiSi

1

2

10

4

10 [GeV]

NN

s 0.1 0.2 0) ≈ (y

+

π /

+

K

NA61/SHINE p+p Be+Be Ar+Sc World p+p Pb+Pb/Au+Au

Ar+Sc placed in between light and heavy systems. Be+Be very close to p+p.

NA61/SHINE Preliminary NA61/SHINE Preliminary

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 24 / 29

Canonical strangeness suppression

Arises due to differences between GC and C formulation. Local conservation of quantum numbers severely reduces the phase space available for particle production.

(Tounsi, Redlich; 2001, arXiv:hep-ph/0111159)

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 25 / 29

System size dependence of strangeness production - SMES

<W> 1 10

2

10

3

10 0) ≈ (y

+

π /

+

K 0.1 0.15 0.2 0.25

p+p Be+Be Pb+Pb NA61/SHINE preliminary NA49 c GeV/ A 30 SMES WNM

SMES predicts very different system size dependence of K +/π+ ratio than the one measured by the NA61/SHINE experiment. System size dependence predicted by SMES is due to diminishing effect of the canonical strangeness suppression with increasing volume within statistical models.

(Poberezhnyuk, Gaździcki, Gorenstein, Acta Phys.Polon. B46 (2015) 10)

p+p Pb+Pb Be+Be

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 26 / 29

System size dependence of strangeness production - PHSD

> 1 10

2

10

3

10 0) ≈ (y

+

π /

+

K 0.1 0.15 0.2 0.25

p+p Be+Be Pb+Pb NA61/SHINE preliminary NA49 c GeV/ A 30

<W> 1 10

2

10

3

10 0) ≈ (y

+

π /

+

K 0.1 0.15 0.2 0.25

p+p Be+Be Pb+Pb NA61/SHINE preliminary NA49 c GeV/ A

• 158

A 150

<W> 1 10

2

10

3

10 0) ≈ (y

+

π /

+

K 0.1 0.15 0.2 0.25

] ] ] ] p+p Be+Be C+C Si+Si Pb+Pb NA61/SHINE preliminary NA49

c GeV/ A

• 158

A 150 WNM pHSD

PHSD predicts increase of strangeness production with system size at low collision energies (<10 GeV) and decrease at high collision energies (>10 GeV). PHSD predictions in disagreement with data at high energies.

(Palmese et al., PRC94 (2016) 044912)

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 27 / 29

Cluster formation

mass number A Large clusters = Fireball Cluster volume Vc ONSET OF FIREBALL Small

• ff-equilibrium

clusters Beginning of the creation of large clusters of strongly interacting matter in nucleus-nucleus collisions with increasing mass number A.

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 28 / 29

The Two Onsets

Onset of deconfinement: beginning of creation of QGP with increasing collision energy (√sNN). Onset of fireball: beginning of creation of large clusters of strongly interacting mater in A+A collisions with increasing nuclear mass number (A).

A √sNN

(collision energy) (atomic mass)

Pb+Pb Ar+Sc Be+Be p+p ≈ 10 ≈ 10

[GeV]

Onset of fireball Onset

• f

deconfinement

(M.L, L. Turko; arXiv:2002.00631)

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 29 / 29

Thank you for your attention!

"It was easier to know it than to explain why I know it." said Sherlock.

• Arthur Conan Doyle 1

1as reminded by J.R. Pelaez in Phys. Rept. 658, 1 (2016)

Backup Slides

Dynamical approach debunked with low energy data

At low energies (AGS), where transition to QGP is not expected, K +/π+ ratio measured in A+A in comparison with p+p was even higher than at SPS and RHIC energies.

(Gazdzicki, Gornestein, Seyboth; Acta Phys.Polon. B42 (2011) 307-351)

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 1 / 7

Statistical Hadronization – γs, γq

Smooth parameter evolution as an argument behind using suppressed phase-space occupancy.

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 2 / 7

Centrality selection

Unique challenge – especially for small ions. p+p: elastic or inelastic Pb+Pb: centrality ↔ multiplicity Neither works for "intermediate" systems: 40Ar+45Sc, 7Be+9Be. → multiplicity depends on physics of interest, → may introduce bias In NA61/SHINE: measurement of forward energy EF of collision spectators in a modular calorimeter (Projectile Spectator Detector). The most central collisions deposit the smallest energy EF. Precise, reproducible, unbiased. Can be only done with fixed-target experiments.

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 3 / 7

The Two Onsets

Percolation approach: Increasing nuclear mass → density of clusters (strings, partons...) increases → Probability of cluster overlapping increases. → Conservation laws act on the whole cluster. This approach does not explain equilibrium properties of large clusters.

Physica A96 (1979) 131-135; Phys. Lett. B97 (1980) 128-130; Nucl. Phys. B390 (1993) 542-558; Phys.

• Rev. Lett 77 (1996) 3736-3738; Phys. Rev. C72 (2005) 024907

AdS/CFT correspondence: AdS (gravity) - formation of a black hole horizon, the information trapping takes place when critical values of model parameters are reached. CFT (QCD) - only starting from a sufficiently large nuclear mass number the formation of the trapping surface in A+A collisions is possible.

• Prog. Part. Nucl. Phys. (2009) 62; Phys. Rev. D79 (2009) 124015

A √sNN

(collision energy) (atomic mass)

Pb+Pb Ar+Sc Be+Be p+p ≈ 10 ≈ 10

[GeV]

Onset of fireball Onset

• f

deconfinement

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 4 / 7

Predictions of SMES

step kink horn

Plateu in "temperature" dependence on collision energy. Enhancement of entropy production in QGP phase (per participating nucleon). Suppresion of strangeness production in QGP phase.

[GeV]

NN

s 1

2

10

4

10 T [MeV] 200 400

+

K

≈ y

Experimental results – confirming SMES predictions. Signatures of PT happen all at the same √sNN.

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 5 / 7

dE/dx distribution

Functions are fitted to experimental data by considering the parameters depending on the absorbing material as free fit parameters:

• −dE

dx

• trunc

= E0 1 β2

• K + ln(γ) − β2 − δ(β, XA, a)

E0 contains all the constant factors. K adjusts for the shape of the curve around the minimum. Parameters fitted to the data: E0, K, XA, a

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 6 / 7

Strangeness suppression in Q-state

gs

W , gs Q – numbers of internal dof of (anti)strangeness carriers in W-, Q-state.

The entropy carried by strange (and antistrange) particles: Ss = gs g S For massless particles of j-th species: Sj = 4Nj, Ns + N¯

s = S

4 gs g And the strangeness to entropy ratio: Ns + N¯

s

S = 1 4 gs g Estimate (for massless dof): Q-state: gs

Q/gQ ≈ 0.22,

W-state: gs

W /gW ≈ 0.5

Numerical calculations with true masses considered: energy dependent

Maciej Lewicki (UWr) Small and large systems @NA61/SHINE Feb 5, 2020 7 / 7