
Relativistic Heavy Ion Collider

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Heavy Ion Collisions: Au + Au √sNN = 7.7, 11.5, 19.6, 27, 39, 62.4, 130, 200 GeV Cu + Cu = 22.4, 62.4, 200 GeV

d + Au = 200 GeV U + U 193 GeV, Cu + Au 200 GeV

Polarized p + p Collisions: √s = 62.4, 200, 500 GeV

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rp +

r p

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p↑ + p↑

STAR


STAR Detector

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


RHIC Discoveries

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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”

- Strong collective flow, even for multi-strange hadrons (, )- Flow driven by Number-of-Constituent-Quark (NCQ) in hadrons

Two most significant discoveries originated in RNC:


HI Physics Focus of RNC

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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/)

• Partonic energy loss

– Jets, high pT correlations

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

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

STAR, QM 2012

Precision measurements of identified particle v2

- push the limits of partonic collectivity - provide constraints to study the sQGP properties

• 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()


Charm production cross section

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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.

• predominantly created from initial hard scatterings in HI collisions.

pQCD

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

Open Charm Hadrons in Au+Au collisions

• Modification in low pT - indication of strong charm-medium interactions.

• Large suppression at high pT - indication of large energy loss in the sQGP.

• Future precision measurements with HFT: RAA, v2, correlations.

Model curves:

He, et al. arX

iv: 1204.4442G

ossiaux, et al. arXiv: 1207.5445

Y. Zhang (now at USTC)

STAR, QM2012


J/ Production

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STAR, QM2012 C. Powell

• Quarkonium production – color screening in sQGP.

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

• J/ freeze-out differently compared to light hadrons- Small (or zero) radial flow- Other production mechanisms (e.g. regeneration)


J/ v2 – Probe Charm Collectivity

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Au+Au 200 GeV 0-80%

• Disfavor regeneration from thermalized charm quarks at pT > 2 GeV/c.

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

STAR, QM2011


Dielectrons at Au+Au 200 GeV

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• Clean penetrating probe to study various stage of HI collisions

• Goals:o In-medium vector mesons

o Thermal radiation

• Enhancement at 0.3-0.7 GeV/c2 compared to the hadron cocktail.

• Vacuum cannot reproduce the excess observed in data.

- in-medium modification

STAR, QM2011 J. Zhao


Energy Dependent Dielectron Production

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• Low mass region (LMR) enhancement persists from 19.6 – 200 GeV.

• In-medium broadening reproduce LMR excesses consistently.- Suggestive of (partial) chiral symmetry restoration.

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

In-medium broadening: R. Rapp, private communications

P. HuckSTAR, QM2012


Beam Energy Scan

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0) Turn-off of sQGP signatures

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

BES Phase-I

RNC initiated and is now leading the BES program at RHIC

NSAC Long Range Plan 2007


Inclusive Charged Hadron v2

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STAR, PRC 86 (2012) 054908 H. Masui, A. Schmah

• Similar v2 behavior over a wide energy range from 7.7 GeV – 2.76 TeV.

v2

Rat

io


Identified Particle v2

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

NCQ scaling between particles and anti-particles is broken!

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

STAR Preliminary

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

STAR, QM 2012


Rcp of Charged Hadrons

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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.- suppression at 200 GeV – partonic energy loss

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


Higher Moments of Net-protons

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

• A non-monotonic behavior could be indicative of the QCD critical point. • Deviation from Poisson expectation. - can be due to other correlation sources

• Current precision cannot allow a firm conclusion on the energy dependence. • Future precision measurements at low energies.

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

STAR QM 2012varianceskewness

kurtosis

STAR, PRL 105 (2010) 022302


Spin Physics at STAR

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€

Sz =1

2=

1

2Δu + Δd + Δs( ) + ΔG + Lz q,g

RNC focus

• Gluon polarization

– Jet double spin asymmetry

• Strange quark polarization

– Hyperon () longitudinal spin transfer

• Transverse spin

– Forward single spin asymmetries (0, )

Nucleon spin structure

25-30% of total spin


Gluon Polarization – Jet Asymmetries

• Non-zero gluon polarization for gluon light-cone momenta at the level of 5-20% of the proton momentum and at hard scales.

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

2006 data

2009 data

DSSV: Florian et al, PRL 101 (2008) 072001


Longitudinal Hyperon Spin Transfer

STAR, SPIN 2012, DNP 2012

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

• New sensitivity to s (s) and polarized fragmentation.

• Unique at RHIC and complementary to deep-inelastic lepton-nucleon scattering.


Transverse Asymmetries: ,

• AN of , – QCD origin of large asymmetries, OAM contribution in nucleon spin.

• NLO pQCD describes the η production cross section at forward rapidity.

• AN of η might be larger than π0 AN.

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


Synergies with Theory Group

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• Jet quenching and partonic 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


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 STAR Physics Focus @ RNC

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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 in heavy ion collisions

4) In preparation of BES-II

5) pA/eA program

– nPDF / evolution from cold nuclear matter to sQGP


High Energy Nucleus-Nucleus Collisions

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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


Future: Thermal Radiation via Di-electrons

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


Future Upgrades

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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 @ RNC

Documents

Transcript of STAR Physics @ RNC