strangeness in star at rhic - indico · 2018. 11. 19. · strangeness in quark matter, 27 june - 1...

1 Strangeness in Quark Matter, 27 June - 1 July 2016

Strangeness in STAR at RHIC

Shusu Shi 施梳苏 for the STAR collaboration

Central China Normal University

华中师范大学


Outline Ø  Introduction

Ø  Collectivity Ø  Multi-strange hadron and ϕ meson v2 Ø  Energy dependence of v2

Ø  Strangeness production Ø  Nuclear modification factors RCP Ø  Baryon/meson ratio

Ø  Summary


Ø  Strange, multi-strange hadrons and ϕ meson

Less sensitive to late hadronic interactions Ø  Ω hyperons and ϕ meson minimal distortion from decay feed- down Good probe for QGP properties and QCD phase transition

φ Ω Ξ Λ

partonic hadronic

π K p

Strangeness

Ø Key observables Ø  Event anisotropy v2 Collectivity Ø  Nuclear modification factor

Partonic energy loss and recombination Ø  Baryon/meson ratio

Parton recombination

STAR measurements at the beam energies of 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV


Large acceptance at mid-rapidity! Time Projection Chamber: Full azimuthal coverage, (|η|<1.0)

Excellent particle identification!

STAR Detectors


Particle Identification

Ø  Reconstruction techniques used Ø  ϕ mesons: invariant mass Ø  Weak decay particles (KS

0, Λ, Ξ, Ω): secondary vertex + invariant mass

)2) (GeV/c-,K+M(K1 1.05 1.1

)-1 )2

dN/d

M (

1 (M

eV/c

0

2

4

6

610×

φ

same event mixed event

)2) (GeV/c-πM(p,1.1 1.15

)-1 )2

dN/d

M (

2 (M

eV/c

0

5

10

15

20610×

Λ

)2) (GeV/c-π,ΛM(1.3 1.35 1.4

)-1 )2

dN/d

M (

1 (M

eV/c

0

0.2

0.4

0.6

610×-Ξ

)2) (GeV/c-,KΛM(1.65 1.7 1.75

)-1 )2

dN/d

M (

1 (M

eV/c

0

2

4

6

8310×

-Ω

)2) (GeV/c-π,+πM(0.45 0.5 0.55

)-1 )2

dN/d

M (

1 (M

eV/c

0

5

10

15

610×

s0K

)2) (GeV/c+π,pM(1.1 1.15

)-1 )2

dN/d

M (

2 (M

eV/c

0

2

4

6

610×

Λ

)2) (GeV/c+π,ΛM(1.3 1.35 1.4

)-1 )2

dN/d

M (

1 (M

eV/c

0

0.1

0.2

0.3

610×+

Ξ

)2) (GeV/c+,KΛM(1.65 1.7 1.75

)-1 )2

dN/d

M (

1 (M

eV/c

0

2

4

310×+

Ω

Au + Au at 62.4 GeV

STAR: Phys. Rev. C 88, 014902 (2013)


Ø  Proton and pion v2 compared with Ω baryon and ϕ meson v2 Ø  High precision data prove that Ω follows the baryon/meson splitting

at intermediate pT range, 2 < pT < 5 GeV/c . First time! The major part of collectivity has been built-up at partonic stage!

STAR: Phys. Rev. Lett.116, 062301 (2016)

Ω Baryon and ϕ Meson v2 Ω and ϕ: good probes of early partonic stage of collision

7 Strangeness in Quark Matter, 27 June - 1 July 2016 7

v2(ϕ) versus v2(p)

Before hadronic rescattering

After hadronic rescattering

Ø  Ideal hydro + hadron cascade (JAM) Ø  Small hadron cross section + hadronic rescattering effect on v2 Mass ϕ > mass p è v2(ϕ) >v2(p) è Break mass ordering for ϕ mesons and protons

Model calculations: T. Hirano et al., ; PRC77, 044909 (2008)


Ø  Model study indicates with increasing hadronic cascade time (more hadronic re-scattering), the v2(ϕ)/v2(p) ratio increases Ø  The ratio v2(ϕ)/v2(p) Is at pT = 0.52 GeV/c in 0-30% -> Possibly due to the effect of late hadronic interactions on the proton v2

v2(ϕ) versus v2(p)

STAR: Phys. Rev. Lett.116, 062301 (2016) Model calculations: T. Hirano et al., ; PRC77, 044909 (2008)


RHIC: NCQ scaling holds within 10% Ø  LHC: The deviation from the NCQ scaling at the

level of +/-20% Ø  Coalescence is the dominant hadronization

mechanism at RHIC in the intermediate pT range

NCQ Scaling - RHIC

(c) 0-30%

= 200 GeVNNsAu+Au,

(d) 30-80%

q/n 2v

0

0.05

0.1

0.15π

KS0K

pφ

Λ

Ξ

Ω

(a) 0-30% (b) 30-80%

2 vS0Fit to K

0 1 2

Dat

a/Fi

t

0.60.8

11.2 (e)

0 1 26

8

1

2 (g)

0 1 2

(f)

0 1 2Fit Error

(h)

(GeV/c)q/nT

p )2 (GeV/cq)/n0-mT

(mSTAR: Phys. Rev. Lett.116, 062301 (2016) ALICE: JHEP06(2015)190

Number of Constituent Quark Scaling


(GeV)NNs0 20 40 60

))X( 2(X

)-v2

(v

0

0.02

0.04

0.06Au+Au, 10%-40%-sub EPη

+Ξ--Ξpp-Λ-Λ

--K+K-π-+π

(a)

(GeV)NNs0 20 40 60

))X( 2(X

)-v2

(v

0

0.02

0.04

pp-0%-10%10%-40%40%-80%

(b)

(GeV)NNs0 20 40 60

2norm

))/v

X( 2(X

)-v2

(v

0

0.2

0.4

0.6

0.8 pp-0%-10%10%-40%40%-80%

(c)

0 20 40 60

)X( 2(X

)-v2v

0

0.02

0.04

0.06 0-80%Λ-Λpp-

--K+K-π-+π

(GeV)NNs

Ø  Significant difference of baryon and anti- baryon v2 observed Ø  New data from 14.5 GeV fit the energy dependency curve

STAR: Phys. Rev. C 93, 014907(2016)

Particle vs. Anti-particle v2


Baryon/Meson Separation

Ø  A splitting between baryons and mesons is observed at all energies except 7.7 GeV and all centralities.

Ø  At 7.7 GeV we are limited by the number of events.

0 1 2 3 40

0.10.20.3 0%-10%7.7 GeV

0 1 2 3 40

0.10.20.3 11.5 GeV

0 1 2 3 40

0.10.20.3 14.5 GeV

0 1 2 3 40

0.10.20.3

2v 19.6 GeV

0 1 2 3 40

0.10.20.3 27 GeV

0 1 2 3 40

0.10.20.3 39 GeV

0 1 2 3 40

0.10.20.3 62.4 GeV

0 1 2 3 40

0.10.20.3 10%-40%p

Λ-Ξ -Ω

+π +Ks0K

φ

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3 40%-80%

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

)2 (GeV/c0-mTm

Particles

STAR: Phys. Rev. C 93, 014907(2016)


Baryon/Meson Separation

Ø  The splitting between baryons and mesons is observed for all energies above 14.5 GeV and also at 14.5 GeV for 40–80%.

Ø  For these energies below 11.5 GeV, we are limited by the number of events.

STAR: Phys. Rev. C 93, 014907(2016)

0 1 2 3 40

0.10.20.3 0%-10%7.7 GeV

0 1 2 3 40

0.10.20.3 11.5 GeV

0 1 2 3 40

0.10.20.3 14.5 GeV

0 1 2 3 40

0.10.20.3

2v 19.6 GeV

0 1 2 3 40

0.10.20.3 27 GeV

0 1 2 3 40

0.10.20.3 39 GeV

0 1 2 3 40

0.10.20.3 62.4 GeV

0 1 2 3 40

0.10.20.3 10%-40%p

Λ+Ξ +Ω

-π -Ks0K

φ

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3 40%-80%

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

0 1 2 3 40

0.10.20.3

)2 (GeV/c0-mTm

Antiparticles


Outline Ø  Introduction

Ø  Collectivity Ø  Multi-strange hadron and ϕ meson v2 Ø  Energy dependence of v2

Ø  Strangeness production Ø  Nuclear modification factors RCP Ø  Baryon/meson ratio

Ø  Summary


Au+Au 200 GeV

Ø Nuclear modification factors at Au+Au 200 GeV Ø Less than unity at high pT

Ø Baryon/meson follow different trends

-> Partonic energy loss and recombination

Ø Baryon/meson ratio at Au+Au 200 GeV Ø Baryon enhancement at

intermediate pT in central collisions

-> Parton recombination

STAR: arXiv:1007.2613

Strangeness Production

Strangeness is sensitive probe


STAR Preliminary

STAR Preliminary

STAR Preliminary

Strangeness Enhancement

Ø  K-, anti-Λ, anti-Ξ and ϕ yields increase significantly with respect to the pion yield as the beam energy increases

STAR Preliminary

most central (0-5%), mid-rapidity

Statistical Hadron gas Model: A. Andronic et al., Nucl. Phys. A 772, 167 (2006)


Nuclear Modification Factors Ø  KS

0 RCP increases with decreasing beam energies -> the partonic energy loss effect less important in lower beam energy

Ø  The cold nuclear matter effect (Cronin effect) starts to take over at lower energies

Ø  RCP differences of particles becomes smaller at √sNN ≤ 14.5 GeV -> indication of different properties of the system compared higher energies

0 1 2 3 40

1

2

3Λ+Λ+

Ξ+-Ξ+

Ω+-Ω0sK

39GeV

STAR Preliminary0 1 2 3 40

1

2

3

27GeV

STAR Preliminary

0 1 2 3 40

1

2

3

19.6GeV


1

2

3

4

14.5GeV

STAR Preliminary

0 1 2 3 40

1

2

3

11.5GeV


1

2

3

7.7GeV

STAR Preliminary

(GeV/c)TP

(0-5

%/4

0-60

%)

cpR

Nuclear modification factor: partonic energy loss and recombination


Ø  The separation of central (0-5%) and peripheral (40-60%) collisions in the ratio less obvious when collision energy ≤ 14.5 GeV: less baryon enhancement

-> possible change of medium property Ø  Need more statistics at lower

beam energies

/KS0 Ratio

0 1 2 3 40

0.2

0.4

0.6

0.8

139GeV


0.2

0.4

0.6

0.8

127GeV

STAR Preliminary

0 1 2 3 40

0.2

0.4

0.6

0.8

119.6GeV


0.2

0.4

0.6

0.8

1 0-5%5-10%10-20%20-30%30-40%40-60%60-80%

14.5GeV

STAR Preliminary

0 1 2 3 40

0.1

0.2

0.3

11.5GeV


0.1

0.2

0.3

7.7GeV

STAR Preliminary

(GeV/c)TP

0 s/K

Λ

Enhancement of baryon at intermediate pT in central collisions: parton recombination

Λ


Ω/ϕ Ratio

Ø  The ratios at 11.5 GeV seem to deviate from the trend observed at

higher beam energies for pT > 2.4 GeV/c Ø  40%-60% peripheral < 0-10% central for 19.6, 27 and 39 GeV Ø  Need more statistics at lower beam energies

STAR: Phys. Rev. C 93, 021903 (2016)


NCQ Scaled Ω/ϕ Ratio

Ø  One single strange quark distribution describes both Ω and ϕ spectra-> quark coalescence production

Ø  Slope (T) from Boltzmann fit changes at 7.7 GeV. Centrality difference? Ø  Decreasing s quark density below 19.6 GeV -> Possible phase transition

STAR: Phys. Rev. C 93, 021903 (2016)


Summary

Ø  Multi-strange hadrons and ϕ meson v2 -> Partonic collectivity and coalescence hadronization ϕ mesons less sensitive to hadronic interactionsØ  Energy dependence of v2 -> Further experimental investigations neededØ  RCP increases with decreasing beam energies -> Partonic energy loss effect less importantØ  The separation of central/peripheral /KS

0 less obvious below 19.6 GeV ->

Possible change of medium propertyØ  Decreasing s quark density below 19.6 GeV -> Possible phase transition

Λ


iTPC upgrade: -1 < η < 1 -1.5 < η < 1.5; pT >125 MeV pT > 60 MeV/c.

EPD upgrade: Greatly improved Event Plane info; Alternative centrality definition

Beam Energy Scan II

Stay tuned for further experimental investigations with BES II focus on √sNN ≤ 20 GeV

ETOF upgrade: New charged hadron PID capabilities for 1.1<|η|<1.6


Backup


0 0.5 1 1.5 2 2.5 3

2v

0.05−

0

0.05

0.1

0.15 mesonφ

19.6 GeV14.5 GeV11.5 GeV7.7 GeV

(GeV/c)T

p

0-80%

ϕ Meson v2

Ø  14.5 GeV: Sizable ϕ meson v2, comparable to 19.6 GeV

Ø  High statistics and more collision energies below 20 GeV needed!

STAR: Phys. Rev. C 93, 014907 (2016) Phys. Rev. C 88, 014902 (2013)

strangeness in star at rhic - indico · 2018. 11. 19. · strangeness in quark matter, 27 june - 1...

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