Risa Nishitan
High Energy Nuclear Physics Grou
2022.02.21 博士論文公開発表会

 

 

p

1
i

￼

Measurements of Higher-Order Cumulantsof Net-Proton Distributionsin 200 GeV p+p Collisions at RHIC-STAR

Introduction

•
•
•
•

QCD phase diagram
Higher-order cumulants
STAR Au+Au results
Physics motivation in p+p collisions

Results••

Acceptance dependence
Multiplicity dependencies of cumulants

Discussion
Data analysis

•
•
•
•
•
•

Particle identi cation
Ef ciency correction
Statistical uncertainties
Effects of pileup
Pileup model
Systematic uncertainties

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Risa Nishitani 2022.02.21
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￼Outline••Baryon number conservation effectComparison between p+p and Au+Au

Summary2

• STAR Collaboration meeting (March 4, 2021)• JPS (March 14, 2021)• CPOD2021 - the International conference on Critical Point and Onset of
Decon nement (March 15-19, 2021)• TCHoU workshops (March 30, 2021)• RHIC & AGS Annual Users' Meeting 2021 (June 8-11, 2021)

Activities• STAR Shift (2019, 2020)• Workshop in Wayne State University (2020)• Physics Working Group Meeting at the STAR experiment• v1 ( ow) meeting• Fluctuation Focus MeetingfiRisa Nishitani 2022.02.21
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Oral Presentations

3

• QCD phase diagram• Higher-order uctuations• C4/C2 for critical point search• C5/C1 and C6/C2 for crossover search• Phase transition in p+p?
• Fluctuations in p+p collisions

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Introduction

4￼

Hadronic gas →QGP

QCD phase diagram

Crossover @ μB=0

Y. Aoki, et al., Nature 443, 675 (2006)

Critical point ?
Experimental searchby Beam Energy Scan (BES)at RHIC-STAR

20-420 MeV
STAR Collaboration, Nuclear Physics A 982, 899-902 (2019)STAR public note, https://drupal.star.bnl.gov/STAR/starnotes/public/sn0493

Risa Nishitani 2022.02.21

Goal : Study the phase diagram of QCD matter5￼Fluctuation = Cumulant, Moment

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6￼

Fluctuations of conserved quantities• Conserved quantity is sensitive to correlation length ξξ diverges near the C.P.

M. A. Stephanov, Phys, Rev, Lett. 102, 032301 (2009)
M. Asakawa, et.al., Phys, Rev, Lett. 103, 262301 (2009)
M. A. Stephanov, Phys, Rev, Lett. 107, 052301 (2011)• Volume terms are cancelled by taking ratio toconnect to baryon number susceptibility,

VT3• Higher-order cumulants and their ratios ofconserved charges are sensitive to phase structure ▶︎

Baryon number (B)Electric charge (Q)Strangeness (S)M. Cheng et al, PRD 79,
074505 (2009)

ΔNq = Nq - Nq

• Statistical baseline ：“Skellam” = Poisson - Poissonʼ
C4/C2 = C5/C1 = C6/C2 = 1
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Difference between two independent Possion distributions7￼Net-proton distributions
Energy dependence of net-proton distributions

STAR Collaboration, Phys. Rev. Lett. 126, 092301 (2021)
STAR Collaboration, arXiv, 2101.12413 (2021)

Net-baryon cumulants can be reconstructed from net-proton cumulants
Asakawa, Kitazawa Phys.Rev.C 86 (2012) 024904

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8

κσ2

C.P.

Non-monotonic beam energy
dependence of κσ2 has been observed
for net-proton uctuations

STAR Collaboration, Phys. Rev. Lett. 126, 092301 (2021)
STAR Collaboration, arXiv, 2101.12413 (2021)

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Fourth-order uctuations for critical point search

Possible signatureof critical point at 2.4-7.7 GeV
9Goal : Identi cation of O(4) chiral criticality on the phase boundary
FRG: Functional Renormalisation GroupWei-jie Fu et al., arXiv, 2101.12413 (2021)
HotQCD, Phys. Rev. D101, 074502 (2020)

PQM: Polyakov loop extended Quark Meson

C5, C6 :chiral crossover transition• Negative for LQCD, FRG, PQM - crossover• Positive for HRG and UrQMD (no QCD transition)
B. Friman et al., Eir. Phys. J. C71 1694 (2011)

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￼

Crossover10

M. S. Abdallah, et.al., Phys. Rev. Lett. 127, 262301 (2021)

A. Bazavov et al, Phys. Rev. D 95, 054504 (2017)
HotQCD Collaboration, Phys. Rev. D 101, 074502 (2020)• From peripheral to central collisions, the values of C6/C2
change from positive to negative at 200 GeV• Lattice QCD calculations at μB = 0 show negative C6/C2
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Sixth-order uctuations for crossover search11• Elliptic

ATLAS Collaboration, Phys.
ow (v2) Rev. C 96, 024908 (2017)• Strangeness enhancement

Indication of QGP signals
in p+p collisions at LHC energies

but still not established
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QGP in p+p at high multiplicity?

ALICE Collaboration, Nature Physics,
13, 535–539 (2017)12￼Previous study

STAR Collaboration, Phys. Rev.
Lett. 112, 32302 (2014)

This study• Statistics is 70 times larger thanprevious results• Multiplicity / acceptancedependence would be available

p+p?

with high statistics dataset

Goal of this study:
Precise determination the physics baseline+ Check the possibility of phase transition in high multiplicity eventsin p+p collisions through the measurements of higher-order cumulants
Risa Nishitani 2022.02.21

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• Particle identi cation• Ef ciency correction• Statistical uncertainties• Effects of pileup• Systematic uncertainties

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Data Analysis

14￼STAR detector• Time Projection Chamber (TPC) : Tracking, PID, Vertex• Time Of Flight (TOF) : Extend proton PID up to pT = 2 GeV/c• Start timing from Vertex Position Detector (VPD)• Electro-Magnetic Calorimeter (EMC)• Zero Degree Calorimeter (ZDC)
TOF

TPC
VPD

Full azimuthal angles,|η| < 1.0

Risa Nishitani 2022.02.21

STAR, Nucl.Instrum.Meth.A 499 624-632, (2003)
15

￼

Event & Track cuts
Event
• Collision vertex is required• along the beam line : |VZTPC| < 30cm
• in transverse direction : |VrTPC| < 2cm• Collision pileups are suppressed by : |VzVPD - VzTPC|<3cm
Track cut
• Distance of Closest Approach : DCA < 1cm• Number of TPC hit : nHitsFit > 20
• For long distance of tracks : nHitsFit/nHitsMax <0.52• Rapidity : |y|<0.5• Transverse momentum : 0.4 < pT (GeV/c) < 2.0

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Protons and antiprotons can be identi ed by TPC and/or TOF
depending on pT regionp• Mass square : 0.6<m2 (GeV/c)2<1.2(GeV/c)2• Proton identi cation in dE/dx : |nσP|<2

p
K- K+

p

Kπ-

π+

π-

fi

fi

p

K+

π+

17

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￼Particle identi cation

• Charged particle multiplicity is de ned in |η|<1.0 excluding (anti)protons.
• Event-by-event net-proton distributions are measured at mid-rapidity.
|η|<1, all charged particles except proton
Multiplicity ≧ 5 used in physics analysis
Ef ciency uncorrected

STAR Preliminary

STAR Preliminary

Charged Particle Multiplicity
Cumulants

X-axis of the resultsfisY-axis of the results
18

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Precise measurements in p+p 200 GeV

• Cumulants are corrected for detector ef

a: charge, ε: efficiency

M. Kitazawa, PRC.86.024904 (2012),
M. Kitazawa and M. Asakawa, PRC.86.024904(2012)
A. Bzdak and V. Koch, PRC.86.044904 (2012),
PRC.91.027901 (2015),
X. Luo, PRC.91.034907 (2015)
T. Nonaka et al, PRC.94.034909 (2016),
A. Bzdak, R. Holzmann, V. Koch, PRC.94.064907(2016)
X. Luo, T. Nonaka, Phys. Rev. C99, 044917 (2019)…

T. Nonaka, M. Kitazawa, S. Esumi,
PRC.95.064912 (2017)

ciency variations on acceptance and multiplicity are taken into account.

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￼

Ef ciency correction19

Ef ciency

from “Embedding simulation” with GEANT: using MC tracks embedded

Detector

into experimental data

TPC
TPC×TOFTPC
TPC×TOF

0.5

TOF
TPC × TOF

Proton00.5

1p (GeV/c)p (GeV/c)Tfi

Risa Nishitani 2022.02.21
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1.5

T

1

2

Fitting function by polynomial2

0.5
0.4<p (GeV/c)<0.8, ProtonT
0.4<p (GeV/c)<0.8, Anti-protonT
0.8<p (GeV/c)<2.0, ProtonT
0.8<p (GeV/c)<2.0, Anti-protonT

2 ≤ RefMult < 30
TPC

TOF matching ef ciency|nσP|<2 ∩ TOF-hit
ε=|nσP|<2 = TPC tracking protons

p Integrated Efficiency

Efficiency

1

fi

￼

TPC ef ciency

0

T

10

20

30

Multiplicityp (GeV/c)
T

20

￼

Statistical uncertainties
General method which can be applied to complicated proceduresin cumulant calculations are needed

Bootstrap method

X. Luo., X. Nu, Nucl. Sci. Tech., 28, 112 (2017)
X. Luo., T. Nonaka, PRC 99, 044917 (2019)100k event<Q4>c=18.962463 (62 data show agreement)
40

Random sampling
#1

#2

#3

#100

<Q4>c

ΔNp

20

…
0

Cn

0

…
#1

#2

Risa Nishitani 2022.02.21#3

Statistical error

#100

50

100

Independent Trials~1σ of total show agreement with mean21• Effects of pileups• Effects on TOF matching ef ciency• Effects on Multiplicity distributions• Necessary number of bins in net-proton distribution

22

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Pileup events in p+p collisions

Two effects are contained at high luminosity events:(1) Increasing of pileup backgrounds.
(2) Decreasing of ef ciency due to higher track density

Au + Au Collisioins 200 GeV

p + p Collisioins 200 GeV

2nd-order polynomial fitting
Uncorrected
Corrected

15<Multiplicity><Multiplicity>

15

Corrected

105Uncorrected
0
0

5000

10000

ZDC Coincidence Rate [Hz](1) < (2)Risa Nishitani 2022.02.21
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Effects of pileups

15000

Uncorrected
10

5

0

0

5

10

15

ZDC Coincidence Rate [kHz](1) > (2)23￼

Effects of pileups
Luminosity<ZDC concidence rate (Hz)>High
MiddleTOF Matching Efficiency

Low

1
Run Index

0.5
2 ≤ RefMult < 30
High luminosity

0|DCA| (cm)

• Large tail in high luminosity→ B.G. : High lumi. > Low lumi.
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Middle luminosity
Low luminosity

Proton
0.5

1

1.5

2

p (GeV/c)p (GeV/c)
T

T

C1 are different in 3 luminosity groups
24

TOF matching ef ciency
ε=|nσP|<2 ∩ TOF-hit|nσP|<2|nσP|<2 ∩ TOF-hit ∩ EMC-hit|nσP|<2 ∩ EMC-hit

ε’ =

1

+EMC
0.5
2 ≤ RefMult < 30
High luminosity
Middle luminosity
Low luminosity

Proton
0

0.5

1

1.5

TOF Matching Efficiency

TOF Matching Efficiency= TPC tracking protons
1

0.5

2 ≤ RefMult < 30
High luminosityp (GeV/c)

Middle luminosity
Low luminosity

Proton0

2

TOF with EMC

0.51p (GeV/c)

T

T

T

1.5

2

p (GeV/c)p (GeV/c)T• TOF match ef ciency change ~10% depending on luminosity• Increasing of backgrounds with luminosity in TPC detected tracks• Deviations between different luminosity results are clearly reduced even in the low pT• TOF with EMC are required for entire pT
25
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Effects on TOF matching ef ciency￼More systematic grouping of luminosity⓪①② ③④ ⑤ ⑥ ⑦ ⑧⑨Grouping by equal number of eventsRun Index
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￼<Multiplicity>

1
Lumi.#0
Lumi.#1
Lumi.#2
Lumi.#3
Lumi.#4

10−1

2nd-order polynomial fitting

15

Normalized Number of Events

Effects on Multiplicity distributions
Uncorrected
Corrected

10−2

10

Lumi.#5
Lumi.#6
Lumi.#7
Lumi.#8
Lumi.#9

10−3

5

10−4

0

0

5

10

Mean
correction

15

ZDC Coincidence Rate [kHz]

10−5

1

10−1

Shape
correction

10−3

10−5
10−6
0

0

20

40

Mean' Corrected Multiplicity
1
Lumi.#0 Mean=7.67
Lumi.#1 Mean=7.88
Lumi.#2 Mean=7.88
Lumi.#3 Mean=7.86
Lumi.#4 Mean=7.84
Lumi.#5 Mean=7.81
Lumi.#6 Mean=7.79
Lumi.#7 Mean=7.78
Lumi.#8 Mean=7.82
Lumi.#9 Mean=7.99

10−1

10−2

10−4

Normalized Number of Events

Normalized Number of Events

10−6

Lumi.#0 Mean=7.60
Lumi.#1 Mean=8.78
Lumi.#2 Mean=9.25
Lumi.#3 Mean=9.57
Lumi.#4 Mean=9.86
Lumi.#5 Mean=10.15
Lumi.#6 Mean=10.45
Lumi.#7 Mean=10.80
Lumi.#8 Mean=11.26
Lumi.#9 Mean=12.09

10

20

10−2
10−3
10−4
10−5

30

Multiplicity

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40

50

10−6
0

10

20

30

40

50

Shape Corrected Multiplicity

27￼

Effects on Multiplicity distributions

Mean corrections
are employed

Average over luminosity

0.2
Lumi.#0
Lumi.#1
Lumi.#2
Lumi.#3
Lumi.#4

0.1

0

10

0.2

Lumi.#5
Lumi.#60.1
Lumi.#7
Lumi.#8
Lumi.#9020

Lumi.#0
Lumi.#1
Lumi.#2
Lumi.#3
Lumi.#4

Lumi.#5
Lumi.#6
Lumi.#7
Lumi.#8
Lumi.#9

20

30

10

Mean Corrected Multiplicity

Shape Corrected Multiplicity

Mean Corrected Multiplicity<χ2>=3.480392

Shape Corrected Multiplicity<χ2>=4.328434

8Counts

8
6
4
2

6
4
2

0

5

10

χ2

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0.3

C2

C2

0.3

Counts• Correction method isdetermined by better
agreement of results fromdifferent luminosity groups• <χ2> of C2 in mean
corrected multiplicity issmaller than in shapecorrection• Same results are shown for
most order of cumulants

0

5

10

χ2

28

￼

Necessary number of bins in net-proton distribution
Mean

1bin
ΔNp

…

σ２

107

107

2bin

C1

105

5bin

105

105

103

103

10

10

10

10−1

10−1

10−1

−5

−3

5 10

0

C2

−5

7bin

−3

5 10

0

−5

0

5

Number of Net-proton
Multiplicity=19

6bin

6bin

103

10−3

ΔNp

107

Multiplicity=19
Lumi.#8

15 Lumi.#9

15

10

10

Statistical error 10

5

5

5

15

Multiplicity=19
Lumi.#2

C6
−0.5

0

distributions have enough number of bins

−0.5

0.5

0

0.5

6

108
(M )

107

Number of Events

Luminosity categorizations so that net-proton

0

Bootstrap C

ΔNp
Statistical errors for each luminosity groups
at high multiplicity bins cannot be properly
estimated due to small number of bins (<6)
in net-proton distributions

−0.5

0.5

105

103

10−1

0-1%

1-2%

10

10

20

30

Mean Corrected Multiplicity

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￼

Summary of systematic study
×100

Large uncertainties in C5, C6/C2

Contribution (Rj) for each variables

×100

DCA is dominant
for most ratios

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￼

Results & Discussion• Acceptance dependence• Multiplicity dependence• Mean corrected multiplicity dependence• Luminosity independent variable dependence
Discussion① :Study of baryon number conservation effectDiscussion② :Comparison between p+p and Au+Au

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￼

Acceptance dependence of net-proton cumulant ratios• Deviations from Skellam baseline become large with increaseΔy dependenceof Δy acceptance except for C3/C2• PYTHIA calculations do not reproduce the observed deviations
Net-Proton Cumulant Ratios

15

C2/C1

SkellamPYTHIA 8
Systematic uncertainties

0.15

0.1

C3/C2

p+p Collisioinss = 200 GeV
0.4 < pT < 2.0 GeV/c, |y| < 0.5
Net-proton

10
0.05

0.2

0.4

0.6

0.2

C4/C2

0.4

0.6

C5/C1

C6/C2

1

1

1

0.5

0.5

0.5

0.2

0.4

0.6

0.2

0.4

0.6

0.2

0.4

0.6

|y| < x• The baseline is suppressed by baryon number conservation
P. Braun-Munzinger et. al., Nucl. Phys. A 961 (2016)

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￼

Acceptance dependence of net-proton cumulant ratios• Deviations from Skellam baseline become large with increase ofΔpT dependencepT acceptance except for C3/C2• PYTHIA calculations do not reproduce the observed deviations
14

C2/C1

SkellamPYTHIA 8 CR-off
Systematic uncertainties

Net-Proton Cumulant Ratios

0.15
12

10

0.1

C3/C2

p+p Collisioinss = 200 GeV
0.4 < pT < 2.0 GeV/c, |y| < 0.5
Net-proton

8
0.05
6
1

2

1

C4/C2

2

C5/C1

C6/C2

1

1

1

0.5

0.5

0.5

1

2

1

2

1

2

0.4 < p < x GeV/c• The baseline is suppressed by baryon numberT conservation
P. Braun-Munzinger et. al., Nucl. Phys. A 961 (2016)

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￼Multiplicity dependence of net-proton cumulants• Cumulants increase with increasing multiplicity• Deviations from Skellam※ become larger for higher-order ※ Skellam = (Poisson)• PYTHIA calculations do not reproduce the observed values except for C5

proton - (Poisson)antiproton

C1

C3
0.04

0.04

0.02

0.02

0.02

0

0

0

Net-Proton Cumulants

0.04

C5

0
0.3

5

10

15

20

0

0.3

C2

0.2

0.2

0.1

0.1

0

5

10

15

10

15

20

0

0.3

C4

5

10

15

20

10

15

20

C6

0.2

0.1

PYTHIA 8 CR-on
PYTHIA 8 CR-off

Multiplicity bin-by-bin
CBWC in 3 ≤ mch < 30
Systematic uncertainty
Systematic uncertainty

0

5

PYTHIA 8 Average CR-on

0

PYTHIA 8 Average CR-off

0

Skellam

20

0

5

10

15

20

0

5

Mean Corrected Multiplicity• The baseline is suppressed by baryon number conservation P. Braun-Munzinger et. al., Nucl. Phys. A 961 (2016)
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￼Multiplicity dependence of net-proton cumulant ratios• C3/C2 is consistent with the Skellam expectations• Deviations from Skellam become larger for higher-order• PYTHIA calculations do not reproduce the observed multiplicity dependence
15

0.2

10

Net-Proton Cumulants

Multiplicity bin-by-bin
CBWC in 3 ≤ Multiplicity < 30
Systematic uncertainty
Systematic uncertainty
SkellamPYTHIA 8 CR-off
PYTHIA 8 CR-on
PYTHIA 8 Average CR-off
PYTHIA 8 Average CR-on

0.1

5

C2/C1
0

5

C3/C2
10

15

20

0

C4/C2

5

10

15

20

C5/C1

C6/C2

1

1

1

0.5

0.5

0.5

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

Mean Corrected Multiplicity• The baseline is suppressed by baryon number conservation P. Braun-Munzinger et. al., Nucl. Phys. A 961 (2016)
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<Multiplicity>

15

Uncorrected
Corrected

10Lumi.#0 Mean=7.60
Lumi.#1 Mean=8.78
Lumi.#2 Mean=9.25
Lumi.#3 Mean=9.57
Lumi.#4 Mean=9.86
Lumi.#5 Mean=10.15
Lumi.#6 Mean=10.45
Lumi.#7 Mean=10.80
Lumi.#8 Mean=11.26
Lumi.#9 Mean=12.09

−4

10

−5

10

0

5

10

15

Lumi.#5
Lumi.#6
Lumi.#7
Lumi.#8
Lumi.#9

10−3

−3

10−4
10−5
10−6

−6

10

Lumi.#0
Lumi.#1
Lumi.#2
Lumi.#3
Lumi.#4

−1

10−2

−2

10

5

1

10

10−1

10

0

Normalized Number of Events

Normalized Number of Events

2nd-order polynomial fitting

1

0

10

20

30

40

50

ZDC Coincidence Rate [kHz]

0

20

40

Mean' Corrected Multiplicity

Multiplicity

Normalized Number of Events< TOF Matched Multiplicity >TOF matched multiplicity
1
Lumi.#0 Mean=2.26
Lumi.#1 Mean=2.26
Lumi.#2 Mean=2.26
Lumi.#3 Mean=2.26
Lumi.#4 Mean=2.26
Lumi.#5 Mean=2.26
Lumi.#6 Mean=2.25
Lumi.#7 Mean=2.25
Lumi.#8 Mean=2.25
Lumi.#9 Mean=2.24

−1

10

4

10−2

3

10−3

2
1
0

0

5

10

15

ZDC Coincidence Rate (kHz)TOF matced multiplicity
distributions become
consistent among

10−4

different luminsosity

10−5

group

10−6
0

10

20

30

40

50

TOF Matched Multiplicity• ZDC coincidence rate dependence of TOF matced multiplicity become at
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Mean corrected multiplicity

TOF matched
tracksAverage number of (anti)proton becomes at as a function of ZDC
coincidence rate by requiring the TOF matching-> TOF matching can reduce background tracks from pileup events
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TOF matched average number of (anti)protons

￼Net-Proton Cumul

Net-Proton Cumul

Net-Proton Cumul

C2 as a function of multiplicity in 2 way
5

10

15

C2

00
20
0.4 0

00

0
0.4
55

C2

C2 C4

0.3

0.2
0.2

0

15

0

20 0

0.3

55

10
10

155

20 0
20

0

15 55

10

20 0
20

CC24

C4C6

00
0.4
10
10 5 0.4

0.3

0.2

0.2
0.2

00

Average0.1
over Lumi.
Lumi.#0
Lumi.#5
Lumi.#1
Lumi.#6
Lumi.#2
Lumi.#70
Lumi.#3
Lumi.#8
Lumi.#4
Lumi.#9

00

10 55

10

155
5

20 0
20

10

5
10
10

15 55

20

C6
C
4

C6

0.2
0.2

Default cut
Average0.1
over Lumi.
Lumi.#0
Lumi.#5
Lumi.#0
Lumi.#5
Lumi.#1
Lumi.#6
Lumi.#1
Lumi.#6
Lumi.#2
Lumi.#7 0
Lumi.#2
Lumi.#7
Lumi.#3 Lumi.#3
Lumi.#80 Lumi.#8
Lumi.#4 Lumi.#4
Lumi.#9 Lumi.#90

10

200.40
20

0.2
0.2

0.2

0.1

5

155

10
10

00
0.4
10 55 0.4

10

15 5
5

20

Mean Corrected Multiplicity
TOF Matched
Multiplicity TOF Matched Multip
Mean Corrected
Multiplicity
10

Mean Corrected Multiplicity<χ2>=3.480392<χ2> =3.58

8

8

6

CountsCounts

TOF matched multiplicity

42>=1.733222<χ2><χ =1.73
2

6

4

2

0

5

10

χ2

0

2

4

6

8

χ2

Deviations of C2 among different luminosity groups are small in TOF matched mutiplicity-> TOF matching multiplicity are employed
Risa Nishitani 2022.02.21

38

￼

TOF matched Multiplicity dependence of net-proton cumulants• Cumulants increase with increasing multiplicity• Deviations from Skellam※ become larger for higher-order※ Skellam = (Poisson)proton - (Poisson)antiproton
0.1

0.1

Net-Proton Cumulants

C1

0.1

C3

C5

0.05

0.05

0.05

0

0

0
PYTHIA 8 CR-on (0.51 × x)

Net-proton cumulants

−0.05

−0.05

Average−0.05

Average CR-on (0.51 × x)

5

10 0.6

C2

5

10

0.6

C4
0.4

0.4

0.2

0.2

0.2

0

0

0

5

10

−0.2

5

10

5

10

C6

0.4

−0.2

Systematic uncertainties

Average CR-off (0.51 × x)

Skellam

0.6

PYTHIA 8 CR-off (0.51 × x)

5

10

−0.2

TOF Matched Multiplicity (x)• The baseline is suppressed by baryon number conservation
Risa Nishitani 2022.02.21

39

￼

TOF matched multiplicity dependence of net-proton cumulant ratios• Decreasing trends are shown in C4/C2, C5/C1, C6/C2 for data & PYTHIA 8• Deviations from Skellam become larger for higher-order
15

C3/C2

15

Net-Proton
Net-Proton
Cumulant
Cumulant
RatiosRatios0.2

Average
PYTHIA
8 CR-on(0.51
× x)
Net-proton
cumulant
ratiosPYTHIA 8 CR-off (0.51 × x)
Average

C3/C2

PYTHIA 8 Average
CR-on
CR-on (0.51× x)(0.51 × x)
Average
CR-offPYTHIA 8 CR-off(0.51
× x)(0.51 × x)

0.2

10
10

Net-proton cumulant ratios

SkellamPYTHIA 8 Average CR-on (0.51 × x)

C2/C1

0.1

C2/C1

PYTHIA 8 Average CR-off (0.51 × x)
Systematic uncertainties
Skellam

0.1

Systematic uncertainties

5

5

10

5

10

C4/C2 510

C5/C1 5

10

5

1

C4/C2

1

C5/C1

C6/C2
1

1

1

1

0.5

0.5

0.5

0.5

0.5

0.5

C6/C2

5

10

5

10

5

10

5

10

5

10

5

10

TOF Matched Multiplicity (x)withincreasing
the multiplicity
TOF
MatchedMultiplicity(x)• C4/C2, C5/C1, and C6/C2 decrease• Multiplicity dependence of PYTHIA 8 qualitatively reproduce observed C4/C2, C5/C1, C6/C2
Risa Nishitani 2022.02.21

40

￼Discussion ①
Baryon number conservation effectRisa Nishitani 2022.02.21

41

Acceptance dependence of cumulants are important to understandthe time revolution of critical uctuations near the QCD critical pointin heavy ion collisions.
M. Sakaida, M. Asakawa, M. Kitazawa,Phys. Rev. C 95, 064905 (2017)• A possibility of probing the early timeuctuations are obtained through therapidity dependence of the secondorder cumulant• Their non-monotonic behaviors as afunction of rapidity show
experimental signals for the existenceof the critical enhancement aroundthe QCD critical point

42

Risa Nishitani 2022.02.21
fl

￼

fl

Rapidity acceptance dependence of cumulants￼

Baryon number conservation effects• The baseline is suppressed by

ALICE Collaboration, Phys. Lett.
B 807, 10 (2020), 135564

baryon number conservation
P. Braun-Munzinger et. al., Nucl. Phys. A 961 (2016)

C2/Skellam

Mean number of proton
measured in small acceptance

Mean number of baryon
measured in full phase spaceprobability given bybinomial• Mean baryon number is given
by PYTHIA 8

Risa Nishitani 2022.02.21

In the ALICE experiment, measuredΔη dependence of C2/Skellam
for Pb+Pb are purely explainedby global baryon number conservation
43

￼

Baryon number conservation effects• Rapidity acceptance dependence of C2/Skellam

C2 / Skellam

1.1• C2/Skellam are below 1-p
at |y|>0.1

1• PYTHIA 8 do not
reproduce measured

0.9

results

Data
0.8

Systematic uncertainties
PYTHIA 8
1-p (from PYTHIA)
0.2

0.4

|y| < xRisa Nishitani 2022.02.21• Observed deviation can
not be explained only bybaryon number
conservation effect44￼Discussion ②
Comparison between p+p and Au+Au collisions at 200 GeV

Risa Nishitani 2022.02.21

45

￼Comparison between p+p and Au+Au collisions at 200 GeV
Check the possibility of phase transition in high multiplicity events

p+p?

in p+p collisions through the measurements of higher-order cumulants

Risa Nishitani 2022.02.21

46

• The trends from p+p collisions t into the centrality dependence of Au+Au collisions• C5/C1 and C6/C2 < 0 for Au+Au central collisions• C5/C1 and C6/C2 > 0 for p+p collisions, while they decrease and show small value atCumulant Ratios

high multiplicity
2(1)C4/C2
1

3
2
1
0
-1
-2
-3
-4
-5

(2)C5/C1

1
0

0

-1

p + p
AverageAu + Au

Net-protons in 200GeV Collisions-1-3|y| < 0.5, 0.4 < p < 2 GeV/c
T

1

10

100

Lattice PRD101(2020)
Pythia(8.2) CR-off
HRG GCE

-2

1000

1

10

100

1000

(3)C6/C2

70

0% 0% 0% 0%-8 0-7 0-6 0-5
6
5
4

0-

40

%

Pythia CR-on
Pythia CR-off
1

10

100

1000

Multiplicity• Only statistical errors are shown for Au+Au results
Au+Au: STAR, Phys.Rev.C 104, 024902 (2021),
C6/C2: M. S. Abdallah, et.al., Phys. Rev. Lett. 127, 262301 (2021)
LQCD : Phys. Rev. D 101, 074502 (2020)

47

Risa Nishitani 2022.02.21
fi￼Comparison between p+p and Au+Au collisions at 200 GeV￼Goal of this study:

Summary

Precise determination the physics baseline+ Check the possibility of phase transition in high multiplicity eventsin p+p collisions through the measurements of higher-order cumulants

p+p 200GeV -> C6/C2 > 0

Au+Au 200GeV -> C6/C2 < 0
Lattice QCD -> C6/C2 < 0

Signal of the QCD phase transition was not observedfor p+p 200GeV collisions.
However, the decreasing trend in high multiplicity events
hints the negative C6/C2.
The measurements at higher collision energies
or larger colliding system will be important
Risa Nishitani 2022.02.21

48

￼

Backup49

The pileup events are included in the cumulant calculations.
In this study, we tried to understand the effect of pileup eventsby modeling a “pileup- lter” based on the data

50

Risa Nishitani 2022.02.21
fi￼• Effect of pileup events

We have tried to model a pileup lter to describe the multiplicity
distributions for the highest luminosity based on the lowest luminosity• Lowest luminosity events are divided into
two sub-groups• Two(three) events are randomly picked up
from each sub-group with the probability
α(β), and they are superimposed• Parameters α=0.89, β=0.11 can explain
the highest luminosity

The effect of pileup events on cumulants
can be studied by using the pileup lter
51
fi

Risa Nishitani 2022.02.21
fi￼

Explain the multiplicity distributions with pileup model

0.1

Lumi.#5
Lumi.#6
Lumi.#7
Lumi.#8
Lumi.#9

Filter on p/pbar
0.1

0.1

lter is applied to
C1
C3 the number of p/pbar
C5 as done
• Once the pileup
Net-Proton Cumulantsfor0.05the multiplicity, the valueof C1 is doubled by
0.05
0.05 construction• On the other hand, such a signi cant difference is not observedin the data
0

0

DataC
10

0.4

20

30 0.4010

20

30 0.4

C4

2
0.2

0.2

0

0

0

10

20

30

10

10

20

C6

0.2

20

30

10

20

Charged Particle Multiplicity• The pileup lter is NOT applied to p/pbar.
52
fi

fi

Risa Nishitani 2022.02.21
fi￼

Lumi.#0
Lumi.#1
Lumi.#2
Lumi.#3
Lumi.#4

Data (Lowest luminosity)

0.1

0.1

Pileup

Net-Proton Cumulants

C1

0.1

C3

C5

0.05

0.05

0.05

0

0

0

0.4

10

20

30 0.4C2

10

20

30 0.4

C4
0.2

0.2

0

0

0

10

20

30

10

10

20

30

20

30

C6

0.2

20

30

10

Charged Particle Multiplicity• C1 : the “pileup- ltered” data show smaller value than the lowest luminosityʼs data
• C2 : Two datas cross and they show the larger deviations than the other orders of cumulants
Risa Nishitani 2022.02.21
fi￼

Data-driven model53

Data vs Data-driven model
Data-driven model
Data (Lowest luminosity)
Data (Lowest luminosity)
Pileup

0.4

Net-Proton Cumulants

0

0.05

5

10

C2

0.2

10
15

C2

200
20
0.4

0.05

C3 C1
0.05

0

30 0.4
5

0.4

10

0.2

0

10
15

10

0.2

0

0

20 0
200.4

5

10

20
20

0.05

C5

0.05
Data and data-driven

0.05

0

20

0.2

0.2

0

0

0.2

0

consistent in terms
of:
0

0

30 0.4 30 0.4
5
10

10
15

10

20 30
30 0.4crossing
point
•

C6 C4

20
20

10

20

C6

• high lumi. < low lumi.
• largest deviation in C2
0.2

0

0

30
5

10

10
15

10

20
20

20

30
5

Charged Particle Multiplicity
Charged Particle Multiplicity

Risa Nishitani 2022.02.21

0.1

C5 C3

C6

0

10
15

0.1

C5
0.05

C4 C2

C4
0.2

0.1

model are qualitatively

00.2

Lumi.#0
Lumi.#5
Lumi.#1
Lumi.#6
Lumi.#2
Lumi.#7
Lumi.#3 0.1 Lumi.#8
Lumi.#4
Lumi.#9

0.1

C3
0.05

0

0.4

0.1

0.1

C1

C1

0.05

￼

0.1

Pileup

Net-Proton Cumulants

0.1

Data

30

10

10
10
15

20
20

20

30

30

10

20

Charged Particle Multiplicity

54

￼

Data vs Data-driven model
Data-driven model

Data

Data and data-driven
model are qualitatively

Data (Lowest luminosity)

Data-driven
model
Pileup0.1

0.1

Net-Proton Cumulants

C1

C3

C5

0.05

0.05

0.05

0

0

0

0.4

5

consistent in terms of:

0.1

10

15

20
0.4

5

C2

10

15

200.4

5

C4

• crossing point• high lumi. < low lumi.
• largest deviation in C2
10

15

20

C6 For the results up to C2,

Results are consistent
0.2

0.2

0.2

between low lumi. and highlumi. after the mean

0

0

5

10

15

20

correction for both data &

0

5

10

15

20

5

model
10

15

20

Mean Corrected Multiplicity

Mean Corrected Multiplicity

The pileup effect can be reasonably suppressed by the mean
correction even if the pileup events cannot be excluded
Risa Nishitani 2022.02.21

55