Study of the QCD Phase Structure through High Energy Heavy Ion Collisions

1. Study of the QCD Phase Structure through High Energy Heavy Ion Collisions • Outline: • QCD Phase Structure • Theoretical and Experimental status • Highlights from RHIC Beam Energy Scan Program • Summary Bedanga Mohanty National Institute of Science Education and Research (NISER)

2. Phase Diagram and Basic Interactions Phase diagram of Water Electromagnetic interaction Precisely known Phase diagram of strong interactions Largely still a conjecture arXiv:1111.5475 [hep-ph]

3. QCD Phase Diagram K. Rajagopal and F. Wilczek, Handbook of QCD Physical systems undergo phase transitions when external parameters such as the temperature (T) or a chemical potential (μ) are varied. Conserved Quantities: Baryon Number ~  Electric Charge ~ Q ~ small Strangeness ~ S ~ small Rich phase structure: -- Phases QGP & Hadronic -- Cross over -- 1st order -- Critical Point

4. QCD Phase Diagram - Experimental Conservation in strong interactions -- Charge -- Baryon number -- Strangeness Vary: T, mB, mS, mQ Nature 448 (2007) 302 Vary beam energy to change Temperature & Baryon Chemical Potential

5. Transition Temperature Prog. Theor. Phys. Suppl. 153, 106 (2004)  ~ g (2/30) gparton ~ 47 g ~ 3 Science 332 (2011) 1525-1528 Nucl. Phys. A 830 (2009) 805c • High Temperature • De-confined state of quarks • and gluons Phys.Rev. D85 (2012) 054503

6. No significant volume dependence Cross-over Nature443:675-678,2006 JHEP 1208 (2012) 053 Phys. Rev. Lett. 110, 012302 (2013) At high T and  = 0 is a cross over.

7. Establishing Quark Gluon Phase Eur.Phys.J. C72 (2012) 1945; Advances in High EnergyPhysics 2013 initial > c (Lattice) STAR: QM2012 At and below 11.5 GeV – Hadronic interactions dominate. Need pA data for a quantitative statement. QGP turned off ? 7

8. Establishing Quark Gluon Phase • PartonicCollectivity • De-confinement • Turned off at low energy ? STAR Preliminary 8 Phys. Rev. Lett., 110, 142301 (2013)

9. Establishing Quark Gluon Phase QM2012: STAR • Possible Local Parity Violation effects • Requires De-confined matter of quarks and gluons • Requires chiral symmetry to be restored At and below 11.5 GeV – Hadronic interactions dominate.

10. QCD Phase structureat mB~ 0 • Close to zero baryonic chemical potential the QCD transition corresponding to a state of de-confined quarks and gluons takes place at high temperature. • First principle QCD calculations suggest it is a cross over. Indirectly supported by experimental data. • Transition temperature using chiral condensates ~ 154 MeV, using Susceptibilities and Polyakov loop ~ 175 MeV – width around 15 MeV

11. Transition Line - Theory JHEP 1104 (2011) 001 • Width of transition line wide • Freeze-out line close to transition line at Lower mB • Larger mB deviations of freeze-out curve from transition line • Interesting T vs. mB dependence at lower beam energies

12. Softening of Equation of State STAR Preliminary • Minimum between 11-20 GeV • Softening of Equation of State ? Theory: D. H. Rischke et al., Heavy Ion Phys. 1, 309 (1995). H. Stoecker, Nucl. Phys. A 750, 121 (2005). J. Brachmann et al., Phys. Rev. C 61, 024909 (2000). L. P. Csernai and D. Rohrich, Phys. Lett. B 458, 454 (1999).

13. QCD Phase structure at mB> T • Transition line from lattice QCD has large uncertainties. • Transition line close to chemical freeze-out line at small mB but deviates at large mB. Interesting trends of T vs. mB at lower energies. • Experimental hints towardsno QCD transition to de-confined state ~ 11.5 GeV center of mass energy. • Directed flow data shows non-monotonic dependence on beam energy – Soft EOS ?

14. Search for Critical Point - Theory Numerical QCD calculations difficult at large mB – sign problem Techniques: Reweighting, Taylor expansion & imaginary potential S. Gupta, QM2009 ActaPhys.Polon.Supp. 5 (2012) 825-835 Phys. Rev. D 78, 14503 (2008); JHEP 0404, 50 (2004) Phys.Rev.D71:114014,2005 Issues (not common to all) : lattice spacing, physical quark mass, continuum limit, Volume Theory still some more work to be done …… need more CPU

15. Search for Critical Point - Experiment Beam Energy Scan Program at RHIC Nuclear liquid-gas transition with a critical end point Observables : Related to correlation length or susceptibility < (N)4> - 3 < (N)2>2 ~ 7 < (N)2> ~ 2 < (N)3> ~ 4.5  S  ~  Phys.Lett. B696 (2011) 459 Phys.Rev.Lett. 105 (2010) 022302 Challenging to measure : Finite size effects < 6 fm Critical slowing down, finite time effects  ~ 2 - 3 fm Phys.Rev.Lett. 107 (2011) 052301 Phys. Rev. Lett. 102, 032301 (2009) No dynamical theoretical estimates exists. Experimentally look for non-monotonic variations with beam energy (T, mB). Phys. Rev. Lett. 91, 102003 (2003) Phys. Rev. D 61, 105017 (2000)

16. Search for Critical Point - Experiment • Central collisions • Deviations from Poissonian • Deviations from transport model • Deviations from peripheral collisions • Higher statistics needed at 7.7 • & 11.5 GeV + a new data point • around ~15 GeV STAR: arXiv: 1309.5681 (submitted to PRL) Phys.Rev.Lett. 105 (2010) 022302

17. More on Net-proton Higher Moments • Below 27 GeV results dominated by protons only • Anti-protons follow Poisson • Protons deviate from Poisson • Net-protons deviate from Poisson

18. More on Net-proton Higher Moments • Comparison with Hadron Resonance Gas Model with exact acceptance. • Deviations from HRG model observed

19. QCD Phase structure: Critical Point • Theory: Lattice QCD calculations have uncertainties. • Some calculations indicate it to lie between 10-30 • GeV beam energy • Experiment: If signal survives hadronization then ruled out for beam energies > 39 GeV • Promising prospects below 39 GeV. • High statistics data set needed below 20 GeV. • Theory+Experiment: Need quantitative dynamical theory calculations with realistic correlation lengths to compare to data. Science 332 (2011) 1525-1528

20. Rich Physics from RHIC - BES NCQ Scaling STAR Preliminary No Jet quenching Jet quenching No NCQ Scaling No NCQ Scaling Softening of EOS NCQ Scaling CME STAR Preliminary Critical point search No CME Caveat: Qualitative picture

21. Summary What is known about the QCD phase diagram and to what degree ? QGP QGP QGP Cross-over Cross-over 154 – 175 MeV 154 – 175 MeV First order Hadron Gas Hadron Gas Hadron Gas AtmB> T: Lattice QCD and Models : CP and transition line (model uncertainties needs to be controlled) Experimental data very intriguing : proton v1 and fluctuations AtmB~ 0 : Lattice QCD: Transition temperature and cross-over Supported by experimental data Experimentally accessible by colliding Heavy-Ions at different beam energies Lattice QCD and experiments suggest there are two distinct phases Beam Energy Scan Program – hints at turn-off of QGP signatures

22. Phase structure: Interesting Possibilities Rept.Prog.Phys. 74 (2011) 014001 Quarkyonic phase (Theoretical)  Experimental signature (Baryon correlations, Photons) ? Nucl.Phys. A830 (2009) 709C-712C Nucl. Phys. A 796, 83 (2007 arXiv:1302.1119