STAR Physics @ RNC
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Transcript of STAR Physics @ RNC
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X. DongNov. 27th, 2012 Director’s Review
STAR Physics @ RNC
Xin DongNuclear Science Division / LBNL
1) QCD in cold nuclear matter
2) QCD in hot nuclear matter
• sQGP properties
• QCD phase structure
3) QCD in nucleon spin structure
STAR
Physics
Program
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X. DongNov. 27th, 2012 Director’s Review
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
€
rp +
r p
€
p↑ + p↑
STAR
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X. DongNov. 27th, 2012 Director’s Review
STAR Detector
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• Large & uniform acceptance at mid-rapidity (exploring forward upgrades)• Excellent particle identification• Fast data acquisition
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X. DongNov. 27th, 2012 Director’s Review
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:
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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()
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X. DongNov. 27th, 2012 Director’s Review
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
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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
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X. DongNov. 27th, 2012 Director’s Review
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)
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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.
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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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
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X. DongNov. 27th, 2012 Director’s Review20
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.
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X. DongNov. 27th, 2012 Director’s Review21
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review27
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
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X. DongNov. 27th, 2012 Director’s Review
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