Probing QCD Matter with QED Fields

Transcription

1 XQCD2014, Stony Brook, June 21, 2014 Probing QCD Matter with QED Fields Jinfeng Liao Indiana University, Physics Dept. & CEEM RIKEN BNL Research Center Research Supported by NSF

2 Outline * Brief Introduction * Chiral Magnetic Effect & Charge Dependent Correlations * Chiral Magnetic Wave & Charge Dependent Flow * Summary & Outlook References: JL, arxiv: [review]; Yin & JL, to appear; Jiang, Huang, JL, to appear; Huang & JL, PRL110(2013)232302; Burnier, Kharzeev, JL, Yee, PRL107(2011) & arxiv: ; Bloczynski,Huang,Zhang,JL, PLB 718(2013)1529 & arxiv: ; Bzdak,Koch,JL, arxiv: [review] 2

3 Introduction 3

4 Probing Matter with E & B Fields Ohm s Law Hall Effect 4

5 Probing QCD Matter with E & B Fields What would be the responses of Quark-Gluon Plasma to external E & B probes? QGP however is an extreme form of matter! What else nontrivial could we have? New interest in century-old quest of fundamental transport properties of matter: response to external fields in chiral matter 5

6 Chiral Anomaly In short: bubbles with nonzero chirality can be created --- locally P- & CP-odd environment! 6

7 Environmental Symmetry Violation ~ E ~B P & CP odd Constraint from neutron EDM in vacuum Can theta become dynamical? Axion dynamics. If true, \theta becomes ENVIRONMENTAL. 6= 0 7 Heavy ion collision could provide the environment for \theta to fluctuate away from 0, where anomalous effects can occur.

8 Chiral Magnetic Effect & Chiral Separation Effect Such local P-Odd bubble can be manifested through an external Maxwell B field --- Chiral Magnetic Effect (CME) [Kharzeev, et al] Vector current: P-odd B field: P-even It happens only because of the nonzero \mu_a A complementary effect: Chiral Separation Effect (CSE) [Son,Zhitnitsky,Metlitski,...] 8

9 Current Generation in External EM Fields Ohm s Law Chiral Magnetic Effect (CME) J_v E YES B YES Mu_A Chiral Separation Effect (CSE) J_A??? YES Mu_A 9

10 CESE Chiral Electric Separation Effect (CESE) - R - L - R E field + L + L + R + R + R + R Imbalance between +/- (nonzero Mu_V) & Imbalance between L/R (nonzero Mu_A) --> Axial current X.Huang & JL, arxiv: , PRL(2013) 10

11 CESE Conductivity: New Transport Coefficient The CESE introduces a new type of transport coefficient. For QED Plasma: For QCD Plasma: 11 X.Huang & JL, PRL(2013); Jiang, Huang, JL, to appear.

12 Summarizing the Effects together Ohm, CME, CSE, CESE: Linearizing the fluctuations: we can find several collective excitation modes In general, mixture of four types of modes (see paper for details): Chiral Magnetic Wave, Chiral Electric Wave, Vector Density Wave, Axial Density Wave. All very nice, but: can we experimentally observe one or more of these effects? 12

13 The Rest of Talk Focus on the Status of: * Search for CME in heavy ion collisions through charge-dependent azimuthal correlation * Search for CMW in heavy ion collisions through charge-dependent azimuthal flow See recent reviews, e.g.: Kharzeev, arxiv: ; JL, arxiv:

14 Strong EM Fields in Heavy Ion Collisions E,B Z EM R 2 A 3m 2 Strongest B field (and strong E field as well) naturally arises! [Kharzeev,McLerran,Warringa;Skokov,et al; Bzdak-Skokov; Deng-Huang; Bloczynski-Huang-Zhang-Liao; Tuchin;...] Out-of-plane orientation (approximately) ~B 14

15 Azimuthal Correlation Patterns experimentally accessible info central -> middle -> peripheral: no correlation -> strong correlation -> very weak correlation Bloczynski, Huang, Zhang, JL, PLB 718(2013)

16 B Corr. with Matter Geometry * strong correlation for mid-central to mid-peripheral events * non-zero correlation between B and 4-th harmonics * very weak correlation between B strength and orientation * similar pattern for different field points 16

17 Chiral Magnetic Effect & Charge Dependent Azimuthal Correlations 17

18 CME & Charge Dipole A dipole charge distribution along out-of-plane direction 18

19 Measure CME via Correlation Voloshin(04) Difference between in- plane and out- of- plane CME predic+on: same- charge pair angular correla+on is near- side (NOT change when charge asymmetry flips) Using: 19

20 Decomposition of Signals Bzdak, Koch, JL PRC81:031901,2010 Out- of- plane projected In- plane projected In- plane back- to- back correla:on So far we do not know any single physical effect of such characteris+cs. More likely there should be mul+ple effects contribu+ng to the correla+ons. Experimental check: e.g. completely different p_t & \eta dependence will tell it 20

21 More Differential Measurements +- correla.on dominated by other effect; certain kinema.c regime shows CME- type signal 21 STAR arxiv:

22 From RHIC to LHC LHC Need quan.ta.ve understanding of how CME as well as backgrounds evolve with collision beam energy. RHIC 22

23 From AuAu to UU Collisions Extrapola+on study from AuAu to UU systems: different effects scale differently AIempts to decompose: CME- like and v2- driven signals: Bloczynski, Huang, Zhang, 23 JL, arxiv:

24 Two-Component Scenario in Data Could one make some sense directly out of data by the two- component picture? STAR, arxiv:

25 Toward Quantitative Modeling It is vital to use state- of- the- art modeling, e.g. anomalous hydro, to quan+fy correla+ons generated by CME + other effects in the same framework Anomalous Hydrodynamics (Son-Surowka;...) 25 Yi Yin & JL, in preparation

26 In Passing: Chiral Vortical Effect If Chiral Magne+c Effect is present, then there should also be Chiral Vor+cal Effect. Kharzeev, Son, arxiv: ~A $ ~u ~B $ ~! 5 ~u CME - - > both charge & baryon currents CVE - - > both charge & baryon currents CVE could be more robust due to significantly longer life:me. 26

27 In Passing: Chiral Vortical Effect from STAR, QM14 Data are indica+ve of baryon separa+on across reac+on plane. 27

28 Chiral Magnetic Wave & Charge Dependent Azimuthal Flow 28

29 The Chiral Magnetic Wave Wave: propagating oscillations of two coupled quantities e.g. sound wave (pressure & density); EM wave (E & B fields) Chiral Magnetic Wave (CMW): coupled evolution of Vector & Axial Charge Densities B field 29 Wave Propagation Direction

30 The CMW Wave Equations Coupling together the CME + CSE: (using susceptibilities to relate chemical potential with charge density) Combined with continuity equations we can get the CMW wave equation: [Kharzeev & Yee, PRD83(2011) ] Dissipative terms like diffusions can be added CMW velocity depends B field and susceptibilities 30

31 From CMW to Charge Quadrupole CMW Predictions: [Burnier,Kharzeev,JL,Yee,PRL2011] * A Dipole of Axial Charge Distribution * A Quadrupole of Vector Charge Distribution 31

32 From CMW to Charge Quadrupole Axial Charge Density Vector Charge Density CMW Predictions: [Burnier,Kharzeev,JL,Yee,PRL2011] * A Dipole of Axial Charge Distribution * A Quadrupole of Vector Charge Distribution 32

33 How To Measure the Charge Quadrupole CMW Predictions [Burnier,Kharzeev,JL,Yee,PRL2011]: * A Quadrupole of Vector Charge Distribution leads to splitting of +/- charge elliptic flow! The Minus v2 is bigger, and the splitting is proportional to net charge asymmetry 33

34 STAR Measurements: Binning the Charge Asym. CMW Predictions: finite intercept: Stephanov & Yee, arxiv: Gang Wang,

35 Centrality Dependence of Charge Quadrupole CMW Predictions [Burnier,Kharzeev,JL,Yee,PRL2011; arxiv: ] In Agreement with STAR Data [Gang Wang, QM2012] 35 Gang Wang,

36 Anomalous Hydrodynamics Using the anomalous hydrodynamics framework (Son, Surowka;...) to simulate the transport of charge density via CMW from Yee & Yin, arxiv: Likely essential: Proper charge initial condition; Proper freeze-out; Proper EoS See also other recent hydro studies: Hongo,Hirono,Hirano, arxiv: ; Taghavi,Wiedemann, arxiv: See also AMPT study by Ma, arxiv:

37 The Newest Measurements from STAR at QM14: charge dependence of higher harmonic flow and its particle ID dependence 37 Both results in consistency with CMW interpretation.

38 Summary * P- and CP-odd domains from topological fluctuations, allowing environmental symmetry violation. * A number of nontrivial effects: CME, CVE, CSE, CESE, CMW. * CME & CVE leads to measurable charge & baryon separation in HIC, and measurements show interesting patterns that could contain CME/CVE signals, and efforts are being made to reduce ambiguity due to background effects. * CME + CSE --> Chiral Magnetic Wave as a collective excitation. Chiral Magnetic Wave induces a charge quadrupole distribution of QGP * This leads to observable splitting of + and - elliptic flow. STAR (preliminary) data show strong evidence of such splitting in agreement with CMW predictions. 38

39 Can We Trace back the Charge Distribution at Very Early Time? n hydrodynamic expansion v n Can we do the same for the charge distribution, i.e. to measure final state observable to infer information about the charge distribution back to early time? * EXP observable: how we measure charge distribution in final momentum space? * Modeling: can we invert the observable back to early time charge distribution in coordinate space? 39

40 Future Measurements: Charge Multiple We can do the same harmonic analysis of charge distributions ---new types of measurement! [Blocynski,Huang,Zhang,JL, PLB2013; JL,Koch,Bzdak,PRC2010] 40

41 BACKUP SLIDES 41

42 Simple & General Argument for CESE Consider small chemical potentials, and L/R currents Now we can put L/R currents into V and A currents: CESE originates from conduction transport and imbalance of charges. 42

43 CESE in Holography Holographic calculation of CESE conductivity in D4/D8 model: µ V µ A /T Pu, Wu, Yang, arxiv:

44 Transverse Momentum Conservation (TMC) u Transverse momentum conserva.on (TMC) as a background effect: u Features: back to back, i.e. nega.ve; independent of charge; 1/N effect; RP- independent but stronger in- plane due to v2. u Results: Bzdak, Koch, JL,PRC83:014905,2011; Also PraD, et al; CME + TMC effects : possibly viable scenario in terms of data, but need more works 44

45 Linking Early Charge Distribution to Final Observable from AMPT study by G. Ma & B. Zhang, arxiv: Final observed dipole can put constraint on the charge dipole distribution from the early time. 45

46 Linking Early Charge Distribution to Final Observable AMPT study by G. Ma, arxiv: Final observed quadruple can put constraint on the charge quadruple distribution from early time. 46

47 Strong Fluctuations of Field & Matter What has been left un-studied: E-by-E azimuthal correlations between B and Matter Geometry 47

48 Importance for Observables This azimuthal correlation is essential for any observable of B field effects CME: looking for charge pair correlation from a dipole along B CMW: looking for a charge quadrupole defined via B direction B field + Anomaly: production of photons with large V2 [Basar,Kharzeev,Skokov, PRL2012; related works by Fukushima, et al] 48

49 Extrapolating AuAu to UU 49

50 Extrapolating AuAu to UU Measuring the charge azimuthal distributions in the Little Bang is feasible, and will provide us very valuable information, and maybe surprises! 50

51 STAR Measurements from BES CMW Predictions [Burnier,Kharzeev,JL,Yee,PRL2011]: The Pi-Minus v2 is bigger 51 Bedanga, QM2011

52 The Data Set In- plane back- to- back correla+on from puzzling sources. What to do? * to understand possible sources of puzzling effect e.g. Bzdak,Koch,JL,PRC(2011) * to find other probes that is most sensi+ve to CME and help disentangle effects 52