
STAR Detector

2

• Large & uniform acceptance at mid-rapidity (exploring forward upgrades)• Excellent particle identification• Fast data acquisition


High Energy Nucleus-Nucleus Collisions

3

Time

Initial hardscatterings

Partonic stage

Hadronicstage

Freeze-out

Nuclear modification factor (RAA)

€

RAA =d2N AA /dpT dy

TAA d2σ /dpT dy

Characterize the medium effect

Elliptic flow (v2) = 2nd Fourier coefficient

Sensitive to the early stage properties


Formation of Strongly-coupled QGP

4

ST

AR

: PR

L. 99 (2007) 112301

Formation of strongly-coupled Quark Gluon Plasma (sQGP)!

v2

ST

AR

: PR

L. 91 (2003) 072304

“Jet Quenching”

Significant suppression in particle yield at high pT in central heavy ion collisions

“Partonic Collectivity”

Significant v2 of multi-strange hadrons (, )Number-of-Constituent-Quark (NCQ) scaling


Physics Focuses of RNC

5

1) Study sQGP Properties• Systematic investigation of partonic collectivity – Identified particle v2

• Chiral properties - Dielectron production • Thermalization - Heavy Quark Production (D-meson, J/)

2) Study QCD phase structure - Beam Energy Scan• Turn-off of sQGP signatures – elliptic flow of identified particles • Search for critical point – high moments of net-proton multiplicity


Recorded Datasets

6


Partonic Collectivity

7

Hiroshi Masui, Md. Nasim (Oct. – Dec. 2011)

STAR, QM 2012

Precision measurements on identified particle v2 from high statistics Au+Au 200 GeV.

• 0-30%: baryon-meson grouping / NCQ scaling holds. • 30-80%: Multi-strange hadron v2 deviate from NCQ scaling at mT-m0>1 GeV/c2. v2()<v2(Ks), v2()<v2()

Precision identified particle v2 data provide constraints to study the sQGP properties.


Charm production cross section

8

X.D., Y. Zhang (now at USTC)

STAR, QM 2011, QM 2012STAR, PRD 86 (2012) 072013

• Charm cross section in p+p consistent with the upper bound of the FONLL (Fixed-Order-Next-to-Leading-Logrithm) pQCD calculation.• Charm cross section in Au+Au follows the Nbin scaling (significantly improved uncertainty).

X. DongNov. 27th, 2012 Director’s Review9

Open Charm Hadrons in Au+Au collisions

• D-mesons freeze out at different stage than light hadrons. • Small hump structure in D0 RAA in low pT – similar in transport model calculations.

- indication of strong charm-medium interactions (caveat: Cronin effect) • RAA in Au+Au collisions suppressed at pT > 3 GeV/c.

- indication of large charm quark energy loss in the sQGP medium.

Model curves: M. He, et al. arXiv: 1204.4442, private communicationsP. Gossiaux, et al. arXiv: 1207.5445, private communications

Y. Zhang (now at USTC)

STAR, QM2011 STAR, QM2012


J/ Production

10

STAR, QM2012 C. Powell

Systematic measurements in p+p, d+Au and Au+Au collisions:

• J/ production in d+Au collisions consistent with EPS09 + abs(3mb).• In Au+Au collisions, BW predictions with same (radial flow velocity) as light hadrons different from data in the low pT

- Small (or zero) radial flow velocity- Other production mechanisms (e.g. regeneration)


J/ v2 – Probe Charm Collectivity

11

L. Grandchamp et al. NPA 790, 415 (2002)

20-60%

Initial production vs. charm quark coalescence High pT low pT

Peripheral Central

• Disfavor regeneration from thermalized charm quarks at pT > 2 GeV/c• To probe charm collectivity cleanly Low pT J/ v2 in (more-) central collisions

H. QiuPaper in Collaboration reviewTo be submitted to PRL soon.

STAR, QM2011


Dielectrons at Au+Au 200 GeV

12

• Clean penetrating probe to study various stage of HI collisions

• Goals:

o In-medium vector mesons

o Thermal radiation

• Data show an enhancement at low mass region compared to the hadron cocktails.

- charm = PYTHIA*Nbin (0.96 mb), real contribution in Au+Au is an open question

• Vacuum cannot reproduce the excess observed in data.

- in-medium modification

STAR, QM2011 J. Zhao


Energy Dependent Dielectron Production

13

• Dielectron mass spectra over a broad energy range.

• LMR enhancement persists down to 19.6 GeV.

• Theoretical calculations of in-medium broadening with similar baryon densities from 19.6 - 200 GeV reproduce LMR excesses consistently.

- Suggestive of (partial) restoration of chiral symmetry

In-medium broadeningR. Rapp: private communications

P. HuckSTAR, QM2012


Future: Thermal Radiation

Transverse momentum spectra slopes: to disentangle charm and QGP radiation - Au+Au result seems to be higher than p+p and PYTHIA charm at ~ 2 GeV. Suggestive of either charm modifications or other sources.

- Future measurements to quantify the correlated charm contribution. -– QGP thermal radiation: Cross section, v2, (M, pT)

J. ZhaoSTAR, QM2011


Beam Energy Scan

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0) Turn-off of sQGP signatures

1) Search for the signals of phase boundary 2) Search for the QCD critical point

BES Phase-I


Inclusive Charged Hadron v2

16

STAR, PRC in press H. Masui, A. Schmah

• pT > 2 GeV/c, consistent v2(pT) from 7.7 GeV to 2.76 TeV• pT < 2 GeV/c, v2 rises with increasing collision energy

Large collectivity / Particle composition


Identified Particle v2

17

• Significant difference between baryon-antibaryon v2 at lower energies.• No clear baryon/meson grouping for anti-particles at <=11.5 GeV.

NCQ scaling (sQGP signature observed at 200 GeV) is broken!

Hadronic interactions play a significant role at √sNN<= 11.5 GeV.

mT-m0 (GeV/c2)

STAR Preliminary

STAR Preliminary

A. Schmah Papers well advanced in the collaboration, to be released soon.

STAR, QM 2012


Higher Moments of Net-protons

18

X.F. Luo (now at CCNU)

STAR, PRL 105 (2010) 022302

• Higher moments - more sensitive to Critical Point induced fluctuations.

• Moments of conserved quantities – susceptibilities from Lattice QCD.

• Net-protons – good proxy for net-baryons.

• Moment products – cancel the volume effect.

varianceskewness

kurtosis

First proof-of-principle measurement


Higher Moments of Net-protons

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• Systematic measurements in various energies and various centralities. • Deviation from Poisson baseline.

• UrQMD shows monotonic behavior.

• Future precision measurements at low energies.

X.F. Luo (now at CCNU)H.G. Ritter

STAR QM 2012varianceskewness

kurtosis


Proton Spin Structure

20


STAR Physics Focus in Future

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2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020

BES-I

HFT/MTD: Heavy Flavor / Dileptons

BES-II (√sNN ≤ 20GeV)

pA/eA program

Precision measurements on HF and dileptons:Quantify the sQGP properties (hot QCD)

Precision measurements on focused energiesMap out the QCD phase structure

Precision measurements on pA and eAStudy QCD in cold matter


Future RNC Focuses

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1) Heavy quark production:

a) Heavy quark collectivity: the degree of thermalization

b) Heavy quark energy loss: parton energy loss mechanism

c) Heavy quark correlations: deep insight into the medium properties

2) Di-lepton production: cross section, v2, (M, pT)

3) In preparation of BES-II

4) pA/eA ….

STAR Physics

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