Measurement of the sixth order
cumulant of net-proton multiplicity
distribution at √sNN = 200GeV from theSTAR experiment
JPS fall meeting @Miyazaki
Toshihiro Nonaka
for the STAR collaboration

Outline✓ QCD phase diagram✓ Search for CP with Higher Moments✓ STAR detector and Proton Identifications✓ Results and Summary

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QCD phase diagram✓ Crossover at μB=0
✓ 1st order phase transition atlarge μB?
✓ Critical point?
✓ Beam Energy Scan Phase I atRHIC, √sNN=7.7, 11.5, 14.5,19.6, 27, 39, 62.4 and 200
GeV in 2010, 2011 and 2014.

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Cumulants of conserved quantities✓ Net-baryon, net-charge and net-strangeness• Sensitive to thecorrelation length• Direct comparison withsusceptibility

arXiv:1512.05038“Skewness”“Kurtosis”✓ Recent net-proton results show
the non-monotonic behaviour
with extended pT region.
X. Luo (STAR collaboration) arXiv:1503.02558v2

T. Nonaka, JPS 2016 fall meeting, Sep.22

4Sixth order cumulant✓ Lattice calculations predict a “smooth crossover” at μB=0.
Y. Aoki, Nature 443, 675(2006)✓ Theoretically the six order cumulant of net-baryon and net-charge
fluctuation change sign near the chiral phase transition.
Friman et al, Eur. Phys. J. C (2011) 71:1694✓ Find a direct evidence for the crossover with measurementof the sixth order cumulant at the STAR experiment.

Friman et al, Eur. Phys. J. C (2011) 71:1694

T. Nonaka, JPS 2016 fall meeting, Sep.22

5STAR results✓ The STAR experiment measured C6/C2 at low pT region at√sNN=200GeV of Run10 datasets (~250M events).
L. Chen (STAR collabration), NPA 904-905(2013)✓ Event statistics is very important for higher orders.
✓ We focus on √sNN=200GeV of Run11 datasets which have
~500M events.

L. Chen (STAR collabration), NPA 904-905(2013)
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Solenoidal Tracker At RHIC

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Proton Identification✓ dE/dx measured with TPC is used for proton
identification at 0.4<pT<0.8 GeV/c✓ The combined PID with m2 from TOF is used at0.8<pT<2.0 GeV/c.

STAR preliminary

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Analysis techniqueχ2/NDF=1.9

1. Centrality determination
Use charged particles except protons inorder to avoid the auto correlation.

DataGlauberSTAR preliminary

Analysis : |y|<0.5, p and pbar
Centrality : |η|<1.0, exclude p and pbar

Refmult3

2. Centrality Bin Width Correction
Calculate cumulants at each multiplicity bin
in order to suppress the volume fluctuation.
X.Luo et al. J. Phys.G40,105104(2013)

3. Statistical error calculation✓ Bootstrap✓ Delta theorem

B. Efron,R. Tibshirani, An introduction to the bootstrap,Chapman & Hall (1993).

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Cumulants up to sixth order✓ The 5th and 6th order cumulants deviate from the linear
expectation seen for 1st to 4th order.
Run11, Au+Au √sNN=200GeV
Efficiency uncorrected, 0.4<pT<2.0 GeV/cSTAR
preliminary

Systematic errors are under study.

NpartT. Nonaka, JPS 2016 fall meeting, Sep.22

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Cumulant ratio✓ Previous STAR results using Run10 datasets are
consistent with Run11 within errors.
✓ Extended pT region gives larger signals compared to thelow pT region.
STAR preliminary

Efficiency uncorrected

Systematic errors are under study.
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Summary✓ Cumulants and cumulant ratios up to 6th order of netproton multiplicity distribution are being measured
with 0.4<pT<2.0 GeV/c and |y|<0.5 in Au+Au collisionsat √sNN=200GeV.
✓ Efficiency correction is ongoing.
✓ Statistical errors are still large. Results from the otherdatasets will be merged in order to extract physics
information.
Au+Au 200GeV

Run10Run11Run14MB events

~350M

~650M

~1.5BRemarks

One TPC
sector deadN/A

HFT installed
Production ongoing

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