Δη dependence of net-charge ﬂuctuations
in Au+Au collisions from the Beam Energy
Scan at the STAR experiment
JPS fall meeting at Miyazaki

Tetsuro Sugiurafor the STAR collaboration

Beam Energy Scan (BESⅠ) 2010-2014
Major goals : Explore the QCD phase diagram,and searching critical point

Varying the center of mass energy
psN N =7.7, 11.5, 14.5 19.6, 39, 62.4,
and 200GeV

We can “scan”
QCD phase diagram(μ value is observed top

increase with decreasing sN N )QCD phase diagram

JPS meeting 2016/9/22 at Miyazaki

2T.Sugiura Univ. of Tsukuba

Event by Event ﬂuctuation
Event by Event ﬂuctuation is powerful tools to explore
the QCD phase diagram
M： Mean

N : net charge … N+σ： Deviation

Nr-th non-central moment is deﬁned by0

S： Asymmetryn-th order cumulant is written as

JPS meeting 2016/9/22 at Miyazaki

3

κ： Peakedness

T.Sugiura Univ. of Tsukuba

D-measure
D-measure is deﬁned by 2 formula
D-measure1…

D-measure2…

h Q2 i
D=4hNch i

Nch = N + + N
Q = N+ N

D0 = hNch i⌫(+ ,dyn)

D0 ⇠ D4Theoretically, it is expected that

QGP ﬂuctuation : D =1-1.5
Hadron ﬂuctuation : D= 3-4
JPS meeting 2016/9/22 at Miyazaki

4T.Sugiura Univ. of Tsukuba

STAR Detector

TPC is used to decide particle trajectory and pT• TOF detector is used to remove pile up event in this analysis•JPS meeting 2016/9/22 at Miyazaki

5

T.Sugiura Univ. of Tsukuba

ALICE and STAR results
Pb Pb ALICE(2.76TeV Pb+Pb)••

PRL 110, 152301 (2013)

As centrality become central, D-measure become small.
As energy become large, D-measure become small

Expanding Δη … we can see the signal of QGP ﬂuctuation?

JPS meeting 2016/9/22 at Miyazaki

6T.Sugiura Univ. of Tsukuba

Correction method
0.5 < |⌘| < 1 …determine centrality|⌘| < 0.5
…used for analysis•

Remove Autocorrelation eﬀect•

Centrality Bin Width Correction•

Eﬃciency Correction•Charge conservation correction (D-measure)
Charge conservation correction have done to avoid eﬀect ofcharge conservation and system size.
hNch iD+4
hNtotal iD

Charged multiplicity
in measured acceptanceTotal charged multiplicity
in all acceptanceIf this correction are applied,
D-measure become large.
JPS meeting 2016/9/22 at Miyazaki

7T.Sugiura Univ. of Tsukuba

QA plot200
180160140

tof_vs_mult
7.7GeV

tof_vs_mult
200GeV500

tof_vs_mult

410

Entries 1499713
Mean x64.12
Mean y
37.61
RMS x
60.47
RMS y
35.23

310

tofmatched

tofmatched

Hits of TOF

450
400
350

10

Mean x177.9

Mean y

104.4

RMS x

154.3

RMS y

87.26

10300

120100210543250

1080

20060150

104010100

21050200tof_vs_mult
Entries 8.995638e+0750

100

150200

250

300

00

1100200300

Refmult

400500600

1Refmult

Hits of TPC

Pile up event has been removed.
(cut under red line)

JPS meeting 2016/9/22 at Miyazaki

8T.Sugiura Univ. of Tsukuba

Centrality Determination
1010105

Refmult2

Eventscor4
hrefEntries
MeanRMS

41497414
58.72
60.34

cor4300

10Entries 1497407
Mean x58.22
Mean y
54.12
RMS x
60.34
RMS y
54.59

250

1032003150

104102

2100

Refmult

101050Refmult2Cor10050100150200250300
Refmult2Cor050100150200250300

1Refmult

Refmult…charged multiplicity in
Refmult2…charged multiplicity in|⌘| < 0.50.5 < |⌘| < 1Refmult2 is used for centrality determination
to remove autocorrelation eﬀects

JPS meeting 2016/9/22 at Miyazaki

9T.Sugiura Univ. of Tsukuba

Scatter plot of N+, N- (7.7GeV)
posi_refmult2

nega_refmult2

posi_refmult2

160

N+

140

410180160

310140410310120120

100100210280

8060601040

10104020

2000Entries 1497407
Mean x54.12
Mean y
15.8
RMS x
54.59
RMS y
16.17

N

180

nega_refmult2

Entries 1497407
Mean x54.12
Mean y
21.98
RMS x
54.59
RMS y
22.98

50

100150200

refmult2

250300posi_nega

1350

0050

100

150

200

250300350

1refmult2

posi_nega
Entries
Mean xMean y
RMS x
RMS y

180
160

149740721.98
15.8 4
22.98
10
16.17

140310N

120
1002108060
40

Linear correlation is seen in
N+ v.s. N-

10200020406080

100120140160

180

1N+JPS meeting 2016/9/22 at Miyazaki

10T.Sugiura Univ. of Tsukuba

Correlation (7.7GeV)

300

300

300

30250

250

250

25200

200

200

15|η|<0.5|η|<0.5|η|<0.5|η|<0.2|η|<0.2|η|<0.2

105050
100
0100
150
50

150
100
200

200150250<N > <N > <N >chch250200ch150-1/ν

150

500

400

400

400

300

300

300

200cccc020500

150

100

100

100

50

50

50

000-50250 0-50050-50
50
100
0100
50
150

100
150
200

150200250<N > <N > <N >
chch

ch

200
250

100

200
100+-,dyn

35500200-1/ν

350+-,dyn

350-1/ν

350+-,dyn40240024002400145100

000-100-100-100-200
250 0-200-20005005010050100150100150200150200250<N > <N > <N >chchchc1, c2 and -1/νdyn seems proportional to <Nch>• c2/<Nch> of |η|<0.2 seems smaller than that of |η|<0.2•

JPS meeting 2016/9/22 at Miyazaki

11T.Sugiura Univ. of Tsukuba

Summary•

We report correlations for 1st to 2nd order cumulants of net-charge,
Nch, and νdyn at diﬀerent eta region at sNN = 7.7 GeV Au+Au collisions atRHIC.

•We conﬁrmed c1, c2 and -1/νdyn are approximately proportional to<Nch> because of volume eﬀect.

•c2/<Nch> of |η|<0.5 seems smaller than that of |η|<0.2Next•

Calculate delta eta dependence of D-measure and cumulant ratiosfrom 7.7GeV to 200GeV and consistency check with publish results.

JPS meeting 2016/9/22 at Miyazaki

12T.Sugiura Univ. of Tsukuba

back up

JPS meeting 2016/9/22 at Miyazaki

13T.Sugiura Univ. of Tsukuba

Data set
RHIC STAR experiment, Beam Energy ScanAu+Au 7.7GeV, 11.5GeV, 19.6GeV, 27GeV, 39.5GeV, 62GeV, 200GeV

0.5 < |⌘| < 1 …used to deﬁne centrality|⌘| < 0.5

…used to net-charge analysis

0.2 < pT < 2.0Run selection…using Niharʼs good run list and Hiroshiʼs bad run list

Event selection
Nihar(published)

My analysis

|Vz|

<30

same

|Vr|

<2same|VpdVz-Vz|<4 (39-200GeV only)

same

Pile up event cut

Tof matched>0.46*(Refmult)-10

same

1414

Track cutAnalysis

Nihar(published)

My analysis

pT

0.2 to 2 (GeV)sameη-0.5 to 0.5

same

nFitPoints

>20

same

DCA

<1cmsame

Track Quality Cut

>0.52

same

nhitsdedx

>10

same

spallation proton cut

nSigmaProton < 2

same

Centrality
Nihar(published)

My analysis|η|

0.5 to 1

samez-vertex correction

done

same

DCA

<3cmsamenFitPoint>10
15

same