star physics
DESCRIPTION
STAR Physics. Xin Dong Nuclear 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 Progaram. STAR Detector. - PowerPoint PPT PresentationTRANSCRIPT
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X. DongNov. 27th, 2012 Director’s Review
STAR Physics
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
Progaram
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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
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
TAA d2σ /dpT dy
Characterize the medium effect
Elliptic flow (v2) = 2nd Fourier coefficient
Sensitive to the early stage properties
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X. DongNov. 27th, 2012 Director’s Review
Formation of Strongly-coupled QGP
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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”
Significant v2 of multi-strange hadrons (, )Number-of-Constituent-Quark (NCQ) scaling
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X. DongNov. 27th, 2012 Director’s Review
Physics Focuses of RNC
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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
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X. DongNov. 27th, 2012 Director’s Review
Recorded Datasets
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X. DongNov. 27th, 2012 Director’s Review
Partonic Collectivity
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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.
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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
• 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).
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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
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X. DongNov. 27th, 2012 Director’s Review
J/ Production
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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)
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X. DongNov. 27th, 2012 Director’s Review
J/ v2 – Probe Charm Collectivity
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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
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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
• 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
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X. DongNov. 27th, 2012 Director’s Review
Energy Dependent Dielectron Production
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• 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
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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
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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 signals of phase boundary 2) Search for the QCD critical point
BES Phase-I
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X. DongNov. 27th, 2012 Director’s Review
Inclusive Charged Hadron v2
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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
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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 (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
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X. DongNov. 27th, 2012 Director’s Review
Higher Moments of Net-protons
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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
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X. DongNov. 27th, 2012 Director’s Review
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
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X. DongNov. 27th, 2012 Director’s Review
Proton Spin Structure
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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 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 ….
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