higher moments of net-kaon multiplicity distributions at star · 2018-11-19 · ji...

Ji Xu(CCNU&LBNL)/[email protected] Strangeness in Quark Matter, June 27 – July 1, 2016

Higher Moments of Net-Kaon Multiplicity Distributions at STAR

Ji Xu fortheSTARCollabora0on Central China Normal University

Lawrence Berkeley National Laboratory

1


Outline

Ø Introduction

Ø  Analysis Techniques and Details

Ø  Results Ø Summary

2


QCD Phase Diagram

l  Crossover at µB=0.

l  First order phase transition

expected at large µB.

l  QCD Critical Point: The end

point of first order phase transition boundary.

l  Where is CP(Critical Point) ?

3

STAR Note 0598


δN( )2∼ξ 2 , δN( )

3∼ξ 4.5 , δN( )

4−3 δN( )

2 2∼ξ 7

χq(n) =

1VT 3 ×Cn,q =

∂ n (p /T 4 )∂ µq( )

n ,q = B,Q,S

4

Ø Sensitive to correlation length (ξ) and probe non-gaussian fluctuations near the Critical Point.

M. A. Stephanov, Phys. Rev. Lett. 102, 032301 (2009). M. A. Stephanov, Phys. Rev. Lett. 107, 052301 (2011). M.Asakawa, S. Ejiri and M. Kitazawa, Phys. Rev. Lett. 103, 262301 (2009).

Ø  Direct connection to the susceptibility of the system.

S. Ejiri et al,Phys.Lett. B 633 (2006) 275. Cheng et al, PRD (2009) 074505. B. Friman et al., EPJC 71 (2011) 1694. F. Karsch and K. Redlich , PLB 695, 136 (2011). S. Gupta, et al., Science, 332, 1525(2011). A. Bazavov et al., PRL109, 192302(12) // S. Borsanyi et al., PRL111,

062005(13) // P. Alba et al., arXiv:1403.4903

Fluctuations of Conserved Quantities(B,Q,S)


Higher Moments (fluctuations)

C1,x =< x >,C2,x =< (δ x)2 >,

C3,x =< (δ x)3 >,C4,x =< (δ x)

4 > −3< (δ x)2 >2

κ > 0

κ = 0κ < 0

“Shape” of the fluctuations can be measured: non-Gaussian moments (cumulants):

44,

2 42,

( ) 3( )

N

N

C N NC

κσ

< − < > >= = −

33,

3/2 32,

( )( )

N

N

C N NSC σ

< − < > >= =

5

κσ 2 =C4,qC2,q

, Sσ =C3,qC2,q

Ø Cumulant Ratios

Figure from wikipedia


Ø We measured the net-particle multiplicity fluctuations: net-charge, net-proton (proxy for net-baryon), net-kaon (proxy for net-strangeness). The main observables are volume independent cumulant ratios.

Theory Experiment

HotQCD,PRL109,192302(2012)WBGroup,PRL111,062005(2013)

6

Experimental Observables

R12Q =C1 /C2

Ji Xu(CCNU&LBNL)/[email protected] Strangeness in Quark Matter, June 27 – July 1, 2016 7

RHIC Beam Energy Scan Phase 1 (BES I)

Ø  In the first phase of the Beam Energy Scan (BES) program at RHIC, eight beam energies have already been analysized from √sNN=7.7GeV to 200GeV.

µB, T : J. Cleymans et al., PRC 73, 034905 (2006)

√s(GeV) Sta0s0cs(Millions)

Year μB(MeV) T(MeV) μB/T

7.7 ~4 2010 420 140 3.020

11.5 ~12 2010 315 152 2.084

14.5 ~20 2014 266 156 1.705

19.6 ~36 2011 205 160 1.287

27 ~70 2011 155 163 0.961

39 ~130 2010 115 164 0.684

62.4 ~67 2010 70 165 0.439

200 ~350 2010 20 166 0.142

Study QCD Phase Structure - Onset of sQGP - Phase boundary and critical point.


TPC TOF

@ Maria & Alex Schmah

STAR Detector

Ø Large, Uniform Acceptance at Mid-rapidity Ø Excellent Particle Identification

8


Ø  PID: Energy loss (dE/dx) in Time Projection Chamber and mass-squared (m2) from Time of Flight are used to identify kaons within 0.2<pT<1.6 (GeV/c) and at mid-rapidity |y|<0.5.

Kaon ID with STAR Detectors

Charged Tracks: 0.2 < pT < 1.6 (GeV/c),|y| < 0.5

TPC 0.2 < pT < 0.4 (GeV/c)

p < 0.6 (GeV/c)

TPC+TOF 0.4 < pT < 1.6 (GeV/c)

p < 2 (GeV/c)


Event by Event Net-kaon Distributions

Effects that need to be addressed to get final moments/cumulants: 1.  Auto-correlation effects. 2.  Effects of volume fluctuations. 3.  Finite detector efficiency .

A. Bzdak, et al. PRC91, 027901 (2015) X.Luo, Phys. Rev. C 91, 034907 (2015) X.Luo, et al. J. Phys. G40,105104(2013)

Ø  Most central collisions have a wider distribution compared with peripheral collisions.

Ø  The peak of the net-kaon distributions shift slightly towards the positive direction as the energy decreases.

20− 0 20

20− 0 20

10

210

310

410

510

610

710

10

210

310

410

510

610

710(a) 7.7GeV

0-5%30-40%70-80%

<1.6(GeV/c),|y|<0.5T

0.2<p

20− 0 20

20− 0 20

10

210

310

410

510

610

710

10

210

310

410

510

610

710(e)27GeV 20− 0 20

20− 0 20

10

210

310

410

510

610

710

10

210

310

410

510

610

710(b) 11.5GeV

STAR Preliminary

20− 0 20

20− 0 20

10

210

310

410

510

610

710

10

210

310

410

510

610

710(f) 39GeV 20− 0 20

20− 0 20

10

210

310

410

510

610

710

10

210

310

410

510

610

710(c) 14.5GeV

20− 0 20

20− 0 20

10

210

310

410

510

610

710

10

210

310

410

510

610

710(g) 62.4GeV 20− 0 20

20− 0 20

10

210

310

410

510

610

710

10

210

310

410

510

610

710(d) 19.6GeV

20− 0 20

20− 0 20

10

210

310

410

510

610

710

10

210

310

410

510

610

710(h) 200GeV

)KN∆Net-Kaon (

Num

ber o

f Eve

nts


Combined Efficiency for K+ and K-

Ø  0.2< pT <0.4 (GeV/c), TPC only Ø  0.4< pT <1.6 (GeV/c), TPC+TOF

Efficiency=Efficiency(Tracking)*Efficiency(TOF match) Ø  The input number is the pT weighted average efficiency.

X. Luo, PRC91, 034907 (2015); A. Bzdak and V. Koch, PRC91, 027901 (2015)


Cumulants for Net-Kaon

0

5

107.7GeV

0

20

40

Au+Au Collisions

<1.6(GeV/c)T

0.2<p|y|<0.5

Net-kaon

0

5

10

0 100 200 300

50−

0

50

11.5GeV

0 100 200 300

14.5GeV

0 100 200 300

19.6GeV

0 100 200 300

27GeV

0 100 200 300

39GeV

0 100 200 300

62.4GeV

0 100 200 300

200GeV

Eff. Corrected

Poisson

0 100 200 300

⟩partN⟨Average Number of Participant Nucleons

1C2C

3C4C

C3 and C4 generally consistent with Poisson expectation.

STAR Preliminary


Centrality Dependence of C3/C2

Ø  The values of Sσ/Skellam are consistent with unity within uncertainties.

0 100 200 300

0 100 200 300

0

1

2

0

1

27.7GeV(a)Net-Kaon

<1.6(GeV/c),|y|<0.5T

0.2<p

Eff. CorrectedPoisson

0 100 200 300

0 100 200 300

0

1

2

0

1

227GeV(e) 0 100 200 300

0 100 200 300

0

1

2

0

1

211.5GeV(b)

STAR Preliminary

0 100 200 300

0 100 200 300

0

1

2

0

1

239GeV(f) 0 100 200 300

0 100 200 300

0

1

2

0

1

214.5GeV(c)

0 100 200 300

0 100 200 300

0

1

2

0

1

262.4GeV(g) 0 100 200 300

0 100 200 300

0

1

2

0

1

219.6GeV(d)

0 100 200 300

0 100 200 300

0

1

2

0

1

2200GeV(h)

)⟩partN⟨Number of Participants (

/Ske

llam

σS


Centrality Dependence of C4/C2

Ø  The values of κσ2 are consistent with unity within uncertainties.

0 100 200 300

0 100 200 300

2−

0

2

4

2−

0

2

47.7GeV(a)

Net-Kaon<1.6(GeV/c),|y|<0.5

T0.2<p

0 100 200 300

0 100 200 300

2−

0

2

2−

0

227GeV(e)

Eff. CorrectedPoisson

0 100 200 300

0 100 200 300

2−

0

2

4

2−

0

2

411.5GeV(b)

STAR Preliminary

0 100 200 300

0 100 200 300

2−

0

2

2−

0

2

39GeV(f) 0 100 200 300

0 100 200 300

2−

0

2

4

2−

0

2

414.5GeV(c)

0 100 200 300

0 100 200 300

2−

0

2

2−

0

2

62.4GeV(g) 0 100 200 300

0 100 200 300

2−

0

2

4

2−

0

2

419.6GeV(d)

0 100 200 300

0 100 200 300

2−

0

2

2−

0

2

200GeV(h)

)⟩partN⟨Number of Participants (

2σκ


Energy Dependence of Net-kaon

Ø  The values of σ2/M increase as the energy increases.

Ø  The values of Sσ/Skellam are

consistent with poisson and negative binomial distribution baseline within uncertainties.

Ø  The values of κσ2 are consistent with poisson and negative binomial distribution baseline within uncertainties.

Ø UrQMD (no Critical Point), shows no

energy dependence for Sσ/Skellam and κσ2.

15

10 210

10

20

30

40

0-5% STAR 70-80% STAR 0-5% Poisson

70-80% Poisson 0-5% UrQMD

0-5% NBD70-80% NBD

<1.6(GeV/c),|y|<0.5T

0.2<pNet-kaonAu+Au Collisions at RHIC(a)

10 210

0

1

2(b)

STAR Preliminary

7 8 910 20 30 40 100 200

2−

0

2(c)

(GeV)NNs

2σκ

/M2σ

/Ske

llam

σS


Beam Energy Scan II

Ø  Inner TPC(iTPC) upgrade : |η| < 1 to | η |< 1.5, better dE/dx resolution and higher tracking efficiency.

Ø  Event Plane Detector (EPD): Centrality and Event Plane Determination. 2.1 < |η| < 5.1 Ø  eTOF Larger rapidity coverage extends PID in forward direction -1.6 < η < -1.1.

More details see talks by Alexander Schmah, Jinlong Zhang, and Chi Yang.

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iTPCproposal:hGp://drupal.star.bnl.gov/STAR/starnotes/public/sn0619BES-IIwhitepaper:hGp://drupal.star.bnl.gov/STAR/starnotes/public/sn0598

eTOFLargerrapiditycoverageExtendsPIDinforwarddirecYon1.05<η<1.5

0 0.5 1 1.5-3

-2

-1

0

1

2

Net-Kaon, 0-5%

= 19.6 GeVNNsAu+Au collisions

STAR Preliminary (GeV/c) < 1.6T0.2 < p

Estimated Error BES IIPoisson Expectation

TPCiTPC

y∆

2σ

κ


Summary Ø STAR new results on collision energy and centrality

dependence of net-Kaon cumulants and their ratios, within the kinematic range [|y|< 0.5, 0.2 < pT < 1.6 (GeV/c))], for Au+Au collisions at √sNN = 7.7, 11.5, 14.5, 19.6, 27, 39, 62.4 and 200 GeV are presented.

Ø The values of net-Kaon’s κσ2 and Sσ/Skellam are consistent with poisson and negative binomial distribution baseline within errors.

Ø BES-II (2019-2020) will improve on Kaon’s: - rapidity, purity, and efficiency - systematic control

higher moments of net-kaon multiplicity distributions at star · 2018-11-19 · ji...

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