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STAR Physics @ RNC

STAR Physics @ RNC. 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 Program. Relativistic Heavy Ion Collider. STAR.

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STAR Physics @ RNC

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  1. STAR Physics @ RNC 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 Program

  2. Relativistic Heavy Ion Collider STAR 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

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

  4. RHIC Discoveries Two most significant discoveries originated in RNC: “Jet Quenching” - Significant suppression in particle yield at high pT in central heavy ion collisions STAR: PRL. 91 (2003) 072304 “Partonic Collectivity” - Strong collective flow, even for multi-strange hadrons (f, W) - Flow driven by Number-of-Constituent-Quark (NCQ) in hadrons v2 STAR: PRL. 99 (2007) 112301 Formation of strongly-coupled Quark Gluon Plasma (sQGP)!

  5. HI Physics Focus of RNC • 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/y) • 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

  6. Partonic Collectivity 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(f)<v2(Ks), v2(X)<v2(L) H. Masui, Md. Nasim (Oct. – Dec. 2011)

  7. Charm production cross section STAR, PRD 86 (2012) 072013 STAR, QM 2011, QM 2012 pQCD X.D., Y. Zhang (now at USTC) • 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.

  8. Open Charm Hadrons in Au+Au collisions STAR, QM2012 Model curves: He, et al. arXiv: 1204.4442 Gossiaux, et al. arXiv: 1207.5445 Y. Zhang (now at USTC) • 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.

  9. J/y Production STAR, QM2012 C. Powell • Quarkonium production – color screening in sQGP. • consistent with a shadowing model + cold nuclear absorption in d+Au. • J/y freeze-out differently compared to light hadrons • - Small (or zero) radial flow • - Other production mechanisms (e.g. regeneration)

  10. J/y v2 – Probe Charm Collectivity STAR, QM2011 Au+Au 200 GeV 0-80% H. Qiu Paper in Collaboration review To be submitted to PRL soon. • Disfavor regeneration from thermalized charm quarks at pT > 2 GeV/c.

  11. Dielectrons at Au+Au 200 GeV J. Zhao STAR, QM2011 • Clean penetrating probe to study various stage of HI collisions • Goals: • In-medium vector mesons • Thermal radiation • Enhancement at 0.3-0.7 GeV/c2 compared to the hadron cocktail. • Vacuum r cannot reproduce the excess observed in data. • - r in-medium modification

  12. Energy Dependent Dielectron Production P. Huck STAR, QM2012 In-medium r broadening: R. Rapp, private communications • Low mass region (LMR) enhancement persists from 19.6 – 200 GeV. • In-medium r 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, a(M, pT)

  13. Beam Energy Scan NSAC Long Range Plan 2007 • 0) Turn-off of sQGP signatures • 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

  14. Inclusive Charged Hadron v2 H. Masui, A. Schmah STAR, PRC 86 (2012) 054908 v2 Ratio • Similar v2 behavior over a wide energy range from 7.7 GeV – 2.76 TeV.

  15. Identified Particle v2 STAR, QM 2012 STAR Preliminary A. Schmah Papers well advanced in the collaboration, to be released soon. • 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.

  16. Rcp of Charged Hadrons STAR, QM 2012 E. Sangaline jet-quenching off • 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.

  17. Higher Moments of Net-protons STAR, PRL 105 (2010) 022302 STAR QM 2012 variance skewness kurtosis • 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

  18. Spin Physics at STAR Nucleon spin structure 25-30% of total spin • RNC focus • Gluon polarization • – Jet double spin asymmetry • Strange quark polarization • – Hyperon (L) longitudinal spin transfer • Transverse spin • – Forward single spin asymmetries (p0, h)

  19. Gluon Polarization – Jet Asymmetries STAR PRL 97 (2006) 252001, PRL 98 (2008) 232003 PRD 86 (2012) 032006, SPIN 2012 2009 data 2006 data DSSV: Florian et al, PRL 101 (2008) 072001 • Non-zero gluon polarization for gluon light-cone momenta at the level of 5-20% of the proton momentum and at hard scales.

  20. 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 Ds (Ds) and polarized fragmentation. • Unique at RHIC and complementary to deep-inelastic lepton-nucleon scattering.

  21. Transverse Asymmetries: p0, h L. Eun STAR, PRD 86 (2012) 051101(R) • AN of p, h – 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.

  22. Synergies with Theory Group STAR, PRL 91 (2003) 172302 Song, PRL 106 (2011) 192301 • Jet quenching and partonic energy loss • Hydrodynamic flow • Correlation / fluctuation • Heavy flavor • Dileptons • Spin Steinheimer, arXiv: 1207.2791 STAR, PRD 86 (2012) 072013 Yuan, PRD 84 (2011) 034019

  23. STAR Physics Focus in Future Precision measurements on HF and dileptons: Quantify the sQGP properties (hot QCD) Precision measurements on focused energies Map out the QCD phase structure Precision measurements on pA and eA Study QCD in cold matter

  24. Future STAR Physics Focus @ RNC • Heavy quark production: • Heavy quark collectivity: • - the degree of thermalization • Heavy quark RAA and correlations: • - parton energy loss mechanism / medium properties • Di-lepton production: cross section, RAA, v2, a (M, pT) • Full jet reconstruction in heavy ion collisions • In preparation of BES-II • pA/eA program • – nPDF / evolution from cold nuclear matter to sQGP

  25. High Energy Nucleus-Nucleus Collisions Time Hadronic stage Initial hard scatterings Partonic stage Freeze-out Observables Nuclear modification factor (RAA) Elliptic flow (v2) = 2nd Fourier coefficient Sensitive to the early stage properties Characterize the medium effect

  26. Future: Thermal Radiation via Di-electrons J. Zhao STAR, QM2011 • 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, a(M, pT)

  27. Future Upgrades Near term 2013- TPC SSD 1) Heavy Flavor Tracker (HFT) RNC leading the Pixel subproject see Jim Thomas’s talk next IST PXL 2) Muon Telescope Detector (MTD) Mid term 2017- Subsystem upgrade at forward rapidity expanding pA/eA physics program

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