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

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] 2

3. QCD Phase Diagram Rich phase structure: -- Phases QGP & Hadronic -- Cross over -- 1 st order -- Critical Point 3 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 K. Rajagopal and F. Wilczek, Handbook of QCD

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

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

6. Cross-over Nature443:675-678,20 06 No significant volume dependence At high T and   = 0 is a cross over. 6 JHEP 1208 (2012) 053 Phys. Rev. Lett. 110, 012302 (2013)

7. Establishing Quark Gluon Phase 77  initial >  c (Lattice) At and below 11.5 GeV – Hadronic interactions dominate. Need pA data for a quantitative statement. QGP turned off ? STAR: QM2012 Eur.Phys.J. C72 (2012) 1945; Advances in High Energy Physics 2013

8. Establishing Quark Gluon Phase 88 Partonic Collectivity De-confinement Turned off at low energy ? STAR Preliminary Phys. Rev. Lett., 110, 142301 (2013)

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

10. QCD Phase structure at  B ~ 0 10  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  Width of transition line wide  Freeze-out line close to transition line at Lower  B  Larger  B deviations of freeze-out curve from transition line  Interesting T vs.  B dependence at lower beam energies JHEP 1104 (2011) 001 11

12. Softening of Equation of State 12 Minimum between 11-20 GeV Softening of Equation of State ? STAR Preliminary 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  B > T 13  Transition line from lattice QCD has large uncertainties.  Transition line close to chemical freeze-out line at small  B but deviates at large  B. Interesting trends of T vs.  B at lower energies.  Experimental hints towards no 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  B – sign problem Techniques: Reweighting, Taylor expansion & imaginary potential Issues (not common to all) : lattice spacing, physical quark mass, continuum limit, Volume Theory still some more work to be done …… need more CPU S. Gupta, QM2009 Acta Phys.Polon.Supp. 5 (2012) 825-835 Phys. Rev. D 78, 14503 (2008 ); JHEP 0404, 50 (2004) Phys.Rev.D71:114014,2005 14

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

16. Search for Critical Point - Experiment STAR: arXiv: 1309.5681 (submitted to PRL) Phys.Rev.Lett. 105 (2010) 022302 16 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

17. More on Net-proton Higher Moments 17 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 18 Comparison with Hadron Resonance Gas Model with exact acceptance. Deviations from HRG model observed

19. QCD Phase structure: Critical Point 19 Science 332 (2011) 1525-1528  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.

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

21. 21 Experimentally accessible by colliding Heavy-Ions at different beam energies QGP Hadron Gas Lattice QCD and experiments suggest there are two distinct phases Beam Energy Scan Program – hints at turn-off of QGP signatures QGP Hadron Gas 154 – 175 MeV Cross-over  t    ~ 0 : Lattice QCD: Transition temperature and cross-over Supported by experimental data QGP Hadron Gas 154 – 175 MeV Cross-over First order  t    > T: Lattice QCD and Models : CP and transition line (model uncertainties needs to be controlled) Experimental data very intriguing : proton v 1 and fluctuations Summary What is known about the QCD phase diagram and to what degree ?

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