The Beam Energy Scan at RHIC

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1 2013 ICNT FRIB, MSU July 31, 2013 The Beam Energy Scan at RHIC Jinfeng Liao Indiana University, Physics Dept. & CEEM RIKEN BNL Research Center 1

2 Outline Brief Intro: High Energy Heavy Ion Collisions The RHIC Beam Energy Scan EOS Toward Nonzero Density Summary 2

3 40 Years of Asymptotic Freedom Nuclear Physics Nobel Prize 2004 Running coupling: 3

4 Asymptotically Free Matter Super-hot super-dense: Quark-Gluon Plasma (QGP) Shuryak (1978) McLerran; Kapusta;... weakly coupled gas of quarks and gluons Collins-Perry; Cabibbo-Parisi (1975) * There exists a limiting temperature/density for hadronic matter. * Quark-gluon matter should be expected at very high temperature/density. * Such early visions have developed into one of today s major frontiers in nuclear physics: to study the condensed matter physics of QCD. * Major tools: heavy ion collisions; lattice QCD; compact star observations; models... 4

5 Thermodynamic Transitions from Lattice QCD (Wuppertal-Budapest) RHIC LHC free QGP a relativistic pion gas More precisely, Hadron Resonance Gas * Two benchmarks at low/high T * A transition regime in the middle * Rapid CROSSOVER --- not 1st or 2nd 5

6 Heavy Ion Collisions RHIC LHC Many others in the past and future: AGS, SPS, CSR, NICA, FAIR, FRIB,... (I will be focusing on the high energy end.) 6

7 Some Basics of Heavy Ion Collisions Involving the Thermal (EoS,fluctuations,etc), Near-Thermal (transport, e.g. viscosity, q-hat), and Far-From-Thermal (the thermalization in galsma) properties of such strongly interacting 7 quark-gluon matter

8 A Color-Opaque Plasma Color blind probe Colorful probe Strong jet quenching: a qualitatively different medium 8

9 Initial geometry in coordinate space The Nearly Perfect Fluid Final hadrons in momentum space Collective Flow: sensitive to viscosity! 9 from: Heinz, et al

10 The Nearly Perfect Fluid Shen, Qiu, Heinz The fluid is so perfect that it even carries initial state fluctuations toward final state harmonic flow! --- strong constraints on shear viscosity! < n s o QGP < 2.5 4

11 Partonic Collectivity The observed flow of various hadrons scales with the Number of Constituent Quarks (NCS)! (Even for phi and Omega) Strong evidence for a significant partonic stage where the flow is developed. 11

12 The Beam Energy Scan at RHIC

13 Explore Phase Diagram of QCD Can we know as much about QCD matter as we know about water? (phase'diagram'of'water) Quest:'how'can'we'explore'this' map '?'! La8ce'QCD'on'the'computer'! 'Compact'star/'cosmology'from'the'sky'!'Heavy'ion'collisions'(HIC)'in'laboratory Different regions are connected by one and same QCD theory! 13 from%%stephanov,%arxiv:

14 Physics Motivation * To reach the high baryon density regime * To map out the parton/ hadron phase boundary * To search for a possible critical end point (CEP) 14

15 BES Runs * RHIC top energy: 200 GeV (130 GeV) * Beam Energy Scan (BES Phase-I) 2010 (Run10): 62.4 GeV; 39 GeV; 7.7 GeV 2011 (Run11): 27 GeV; 19.6 GeV * Beam Energy Scan (Phase-II) 2015~2017: ~10 times more luminosity; additional collision energies; other species? fixed target? 15

16 Measurements STAR PHENIX MRPC ToF Barrel EMC Barrel EMC End Cap BBC TPC HLT PMD FTPC Many particle species have been measured: pions, kaons, protons, Xi, Lambda, phi, Omega, heavy flavor; yields, flow, correlations,... 16

17 Particle Ratios pi-/pi+: not much change p-bar/p: clear decrease from: STAR 17

18 Chemical Freeze-Out Condition 18 Andronic, et al, arxiv:

19 How Far Can We Reach? J. Randrup & J. Cleymans, Phys. Rev. C 74 (2006) Computed with freezeout parameters, assuming hadron resonance gas model 19 Randrup & Cleymans, arxiv:

20 Phase Boundary: Jet Quenching Suppression turning off around 10~20GeV 20

21 Phase Boundary: NCQ Scaling STAR Preliminary Partonic collectivity turing off around 10~20GeV STAR Preliminary 21

22 cos( ) Dynamical Correlations STAR Preliminary 200 GeV Au+Au 39 GeV Au+Au 27 GeV Au+Au Opposite sign Same sign - 2 ) cos( GeV Au+Au 11.5 GeV Au+Au 7.7 GeV Au+Au % Most Central % Most Central % Most Central * Azimuthal angle correlations of same-charge and opposite-charge pairs * The same-/opposite-charge pair correlations difference may come from mechanisms specific to QGP formation (e.g. Chiral-Magnetic-Effect) * Such difference disappears around 10~20GeV 22

23 The QCD Critical End Point (CEP) Fodor&Katz, 2004 Gavai&Gupta, 2008 T E =162+/-2 MeV! μ E =360+/-40 MeV T E /T c =0.94+/-0.01! μ E T E =1.8+/-0.1 Experimentally accessible region! 23

24 Observables for CEP Look for specific patterns of conserved charge fluctuations which scale with correlation length (Stephanov) < (δn) 2 > ~ ξ 2 < (δn) 3 > ~ ξ 4.5 < (δn) 4 > - 3 < (δn) 2 > 2 ~ ξ 7 Skewness C N N S = = ( C ) Kurtosis κ 3 3, N < ( < > ) > 3/2 3 2, N σ C N N 4 4, N < ( < > ) > = = 2 4 ( C2, N ) σ 3 Non-monotonic dependence of skewness with collision energy 24

25 Results from BES 2 σ = < ( N < N > ) > s = 3 < ( N < N > ) > σ 3 4 < ( N < N > ) > κ = 3 4 σ Indications around 10~20GeV? --- Not conclusive and in need of more data. --- Also caveats (e.g. only measuring net protons) 25

26 Exploring Phases of QCD 26 from: Nu Xu

27 EOS Toward Nonzero Density

28 Charge Fluctuations & Correlations Conserved charges in QCD: Baryon number, Isospin, Strangeness, Electric µy Z Z Z Z Susceptibilities [...]e µ X N X e µ Y N Y [...] µ 2 X Z [...]NXe 2 µ X N X e µ Y N Y [...] < NX 2 > [...]N X N Y e µ X N X e µ Y N Y [...] < N X N Y > 28 Taylor expansion can be used to extrapolate to nonzero density!

29 Two Benchmarks of The Susceptibilities Let us take baryonic number fluctuation as an example, and examine two simple cases: A gas of heavy fermions with charge B (e.g. as baryonic gas) A gas of massless fermions with charge B (e.g. as S.B. limit) N-th order susceptibilities ~ B^n : quarks B=1/3, baryons B=1 29

30 Quadratic Susceptibilities from (2+1)-f Lattice QCD * HRG at low T * SB limit at high T * nontrivial pattern in transition regime JL, et al, PRD2007,NPB2009,JHEP2013 Wuppertal-Budpast group results (BNL-Bielefield results are consistent)

31 Higher Order Susceptibilities BNL-Bielefeld Constructing EOS with Taylor expansion --- how far can we go? 31 κσ 2 ~ χ (4) (3) χ,sσ ~ (2) χ χ (2),σ 2 M ~ χ (2) χ (1) Connection with measured moments of net charge distributions

32 Constraining EOS: BES HIC vs Hydro b) GeV Au+Au, 0-80% -sub EP p K K 0 s 11.5 GeV 19.6 GeV 0 v GeV 39 GeV 62.4 GeV m T -m 0 (GeV/c ) EOS is input for hydro --- however: * significant contributions from hadronic reactions? * uncertainty of thermalization, EOS, viscosity. * nevertheless important and interesting approach 32

33 Holographic Models of QCD We may use holography to extract insights about strongly interacting dense matter. D4-D8 Model 33 D3-D7 Model

34 EOS of Dense Phase from Holography (Preliminary Results) 34

35 Summary RHIC top energy & LHC: QGP as a color-opaque, nearly perfect fluid. RHIC Beam-Energy-Scan: reaching dense ~1/2 rho_0 (but still hot) regime; constraining the phase boundary; searching for QCD Critical End Point Efforts toward finite density EOS: lattice QCD determination of susceptibilities; BES flow measurements against hydro; QCD-related models. THANK YOU! 35