
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

Nbind2N pp /dpT dy

Characterize the medium effect

Elliptic flow (v2) = 2nd Fourier coefficient

Sensitive to the early stage properties

Observables


RHIC Discoveries

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


HI Physics Focus of RNC

5

1) Study sQGP Properties

• Systematic investigation of partonic collectivity

– Identified particle v2

• Chiral properties / thermal radiation

– Dielectron production (energy dependence)

• 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

– Rcp of charged hadrons

• Search for critical point

– high moments of net-proton multiplicity


Partonic Collectivity

6

H. 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

7

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

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

• Heavy quarks – Sensitive to degree of thermalization of early system.

• consistent with the pQCD calculation in p+p.

• Nbin scaling from p+p to central Au+Au with significantly improved precision.- Charm quarks predominantly created from initial hard scatterings.

pQCD

X. DongNov. 27th, 2012 Director’s Review8

Open Charm Hadrons in Au+Au collisions

• D-mesons freeze out earlier than light hadrons. • Modification in low pT - indication of strong charm-medium interactions. • Large suppression 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

BW fit

BW – Blast Wave model


J/ Production

9

STAR, QM2012 C. Powell

• Quarkonium production – color screening in sQGP.

• consistent with a shadowing model + cold nuclear absorption in d+Au.

• Blast wave prediction with same (radial flow velocity) as light hadrons different from J/ data in the low pT

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


J/ v2 – Probe Charm Collectivity

10

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

11

• 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

12

• Low mass region (LMR) enhancement persists from 19.6 – 200 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 broadening: R. 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, RAA, v2, (M, pT)

J. ZhaoSTAR, QM2011


Beam Energy Scan

14

0) Turn-off of sQGP signatures

1)Search for the phase boundary 2) Search for the critical point

BES Phase-I


Inclusive Charged Hadron v2

15

STAR, PRC 86 (2012) 054908 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

16

• 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


Rcp of Charged Hadrons

17

jet-quenching off

STAR, QM 2012 E. Sangaline

€

RCP =dN /dpT /Nbin( )

0−5%

dN /dpT /Nbin( )60−80%

• Significant change in the charged hadron Rcp at low energies.

• Similar behavior in HIJING with no partonic energy loss at low energies.- Cronin effects

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


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 – related to 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

19

• 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


Spin Physics at STAR

20

€

Sz =1

2=1

2Δu+ Δd + Δs( ) + ΔG + Lz q,g

RNC focus

• Gluon polarization

– Jet double spin asymmetry

• Strange quark polarization

– Hyperon () spin transfer

• Transverse spin phenomena

– Forward single spin asymmetries (0, )

Nucleon spin structure

25-30% of total spin


Gluon Polarization – Jet Asymmetries

• Sizable gluon polarization for gluon light-cone momenta at the level of 5-20% of the proton momentum and at hard scales.• Numerous sustained RNC contributions to this program.

STARPRL 97 (2006) 252001, PRL 98 (2008) 232003 PRD 86 (2012) 032006, SPIN 2012

2006 data

2009 data


Longitudinal Hyperon Spin Transfer

STAR, SPIN 2012, DNP 2012

• New sensitivity to strange (anti-)quark polarization and polarized fragmentation.• Unique at RHIC and complementary to deep-inelastic lepton-nucleon scattering.

Non-relativistic naive quark model, all quarks contribute equally to DLL,

Non-relativistic naive quark model, only strange quarks contribute DLL,

Deep-Inelastic-Scattering like contributions to DLL.

R. Cendejas (now at Penn. State. Univ.)E. Sichtermann


Transverse Spin Phenomena

• η/π0 ratio consistent with the expectation from fragmentation.• NLO pQCD describes the η production cross section at forward rapidity.• The transverse asymmetry AN for the η might be larger than π0 AN.

STAR, PRD 86 (2012) 051101(R) L. Eun


Synergies with Theory Group

24

• Parton energy loss

• Hydrodynamic flow

• Correlation / fluctuation

• Heavy flavor

• Dileptons

• Spin

STAR, PRL 91 (2003) 172302

Song, PRL 106 (2011) 192301

Steinheimer, arXiv: 1207.2791

STAR, PRD 86 (2012) 072013

Yuan, PRD 84 (2011) 034019


Future Upgrades

25

Near term 2013-TPC

SSD

ISTPXL

1) Heavy Flavor Tracker (HFT) RNC leading the Pixel subproject see Jim Thomas’s talk next

2) Muon Telescope Detector (MTD)

Mid term 2017-

Subsystem upgrade at forward rapidity expanding pA/eA physics program


STAR Physics Focus in Future

26

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 STAR Physics Focus @ RNC

27

1) Heavy quark production:

a) Heavy quark collectivity:

- the degree of thermalization

b) Heavy quark RAA and correlations:

- parton energy loss mechanism / medium properties

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

3) Full jet reconstruction

4) In preparation of BES-II

5) pA/eA program

– nPDF / evolution from cold nuclear matter to sQGP

star physics

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