♥ Introductory remarks (what is the CME ?) ♥ E lectromagnetic field created by HIC

1. Lecture 2. Evolution of electromagnetic field in HIC and the Chiral Magnetic Effect ♥ Introductory remarks (what is the CME ?) ♥ Electromagnetic field created by HIC (Phys. Rev. C84, 035202 (2011)) ♥Analysis of CME experiments (Phys. Rev. C 85, 034910 (2012), arXiv:1208.2518) ♥Conclusions

2. Hot quark soup produced at RHIC

3. Energy of gluonic field is periodic in NCSdirection (~ a generalized coordinate)‏ NCS= -2 -1 0 1 2 Instantons and sphalerons are localized (in space and time) solutions describing transitions between different vacua via tunneling or go-over-barrier Dynamics is a random walk between states with different topological charges. Parity violation in strong interactions In QCD, chiral symmetry breaking is due to a non-trivial topological effect; among the best evidence of this physics would be event-by-event strong parity violation. The volume of the box is 2.4 by 2.4 by 3.6 fm. The topological charge density of 4D gluon field configurations. (Lattice-based animation by Derek Leinweber) In the vicinity of the of the deconfinement phase transition QCD vacuum can posses metastable domain leading to P and PC violation

4. Topological charge fluctuations in gluodynamicalvacuum Buividovich, Kalaijan, Polikarpov

5. Chiral magnetic effect These transitions with changing the topological charge involve configurations which may violate P and CP invariance of strong interactions. Fermions can interact with a gauge field configurations, transforming left- into right-handed quarks and vice-versa via the axial anomaly and thus resulting in generated asymmetry between left- and right-handed fermions. In this states a balance between left-handed and right-handed quarks is destroyed, NL-NR=2NFQw→ violation of P-, CP- symmetry. Dynamics is a random walk between states with different topological charges. Average total topological chargevanishes <nw>=0 but variance is equal to the total number of transitions <nw2>=Nt In the presence of inbalanced chirality a magnetic field induces a current along the the magnetic field.

6. D. Kharzeev, PL B633, 260 (2006); D. Kharzeev. A. Zhitnitsky, NP A797, 67 (2007); D. Kharzeev., L. McLerran, H. Warringa, NP A803, 227 (2008). Chiral magnetic effect Red arrow - momentum; blue arrow - spin; In the absence of topological charge no asymmetry between left and right (fig.1) ;the fluctuation of topological charge (fig.2) in the presence of magnetic field induces electric current (fig.3)

7. L or B Charge separation in HIC: CP violation signal Magnetic field through the axial anomaly induces a parallel electric field which will separate different charges Non-zero angular momentum (or equivalently magnetic field) in heavy-ion collisions make it possible for P- and CP-odd domains to induce charge separation (D.Kharzeev, PL B633 (2006) 260). Electric dipole moment of QCD matter ! Measuring the charge separation with respect to the reaction plane was proposed by S.Voloshin, Phys. Rev. C70 (2004) 057901.

8. Charge separation:lattice results Charge separation is confirmed by lattice calculations Lattice gauge theory The excess of electric charge density due to the applied magnetic field. Red — positive charges, blue — negative charges. P.V.Buividovich et al., PR D80, 054503 (2009)

9. Charge separation in RHIC experiments Measuring the charge separation with respect to the reaction plane was proposed by S.Voloshin, Phys. Rev. C70 (2004) 057901. STAR Collaboration, PRL103, 251601 (2009) 200 GeV 62 GeV Combination of intense B and deconfinement is needed for a spontaneous parity violation signal

10. Qualitative estimate of the CME QS -- saturation momentum, The generated topological charge Γs ~ λ2 T4 (SUSY Y-M)‏ Sphaleron transition occurs only in the deconfined phase, the lifetime is

11. Analysis strategy Average correlators are related to the topological charge (D .Kharzeev, Phys. Lett. B 633 (2006) 260)‏ For numerical estimates At the fixing point

12. Magnetic field calculation The Lienart-Wiechard potential is applied to the time evolution of heavy-ion collisions within the UrQMD model Retardation condition with the retardation condition • Field will have only By nonzero component • Field will be negligible for low bombarding energies ■For ultrarelativstic energies the magnetic field is felt by particles closeto the transverse plane • For symmetry reasons the magnetic field is negligible for small b V.Skokov, A.Illarionov, V.T, IJMP A24, 5925 (2009)

13. Magnetic field and energy density evolutionin Au+Au collisions at b=10 fm UrQMD eBy ε [~2π/Sd ] Bcrit ≈ (10. — 0.2) mπ2 [~(αST)2] and εcrit ≈ 1 GeV/fm3

14. From Kharzeev

15. Characteristic parameters for the CME The lifetimes are estimated at eBcrit=0.2mπ2 and εcrit=1 GeV/fm3 for Au+Au collisions with b=10 fm (KAu=2.52 10-2 ) • For all energies of interest τB<τε • The CME increases with energy decrease till the top SPS/NICA energy • If compare √sNN = 200 and 62 GeV, the increase is too strong !

16. Normalized at b=10 fm (centrality 0.4-0.5)for Au+Au collisions The calculated CME for Au+Au collisions Calculated correlators for Au+Au (b=10 fm) collisions at √sNN=200 and 62 GeV agree with experimental values for eBcrit ≈ 0.7 mπ2 , K=6.05 10-2.No effect for the top SPS energy! In a first approximation, the CME may be considered as linear in b/R (D.Kharzeev et al., Nucl. Phys. A803, 203 (2008) )

17. Transport model with electromagnetic field The Boltzmann equation is the basis of QMD like models: Generalized on-shell transport equations in the presence of electromagnetic fields can be obtainedformally by the substitution: A general solution of the wave equations is as follows For point-like particles

18. For a single moving charge (HSD calculation result) Magnetic field evolution A two neutron star collision For two-nuclei collisions, artist’s view: arXiv:1109.5849

19. Au+Au(200) b=10 fm Magnetic field evolution V.Voronyuk, V.T.et al.,Phys. Rev. C84, 035202 (2011)

20. Magnetic field and energy density correlation Au+Au(200) b=10 fm V.Voronyuk, V.T.et al.,Phys. Rev. C84, 035202 (2011)

21. Time dependence of eBy D.E. Kharzeev et al., Nucl. Phys. A803, 227 (2008)Collision of two infinitely thin layers (pancake-like) V. Voronyuk, V. T. et al.,PR C84, 035202 (2011) ● Until t~1 fm/c the induced magnetic field is defined by spectators only. ● Maximal magnetic field is reached during nuclear overlapping time Δt~0.2 fm/c, then the field goes down exponentially.

22. Fluctuation of electromagnetic field Full width is about 2/mπ2 for all transverse field components “Thin disk” overestimated the width by factor about 3 <|EX|> ≈ <|EY|> ≈ <|BX|> V.Voronyuk et al., Phys.Rev. C84, 035202 (2011) restrictedA.Bzdak, V.Skokov, Phys.Lett. B710, 171 (2012) thin disk W.Dend, X.Huang, Phys.Rev. C85, 044907 (2012) HIJING V.T. et al., arXiv:1208.2518 PHSD A

23. Electric field evolution Electric field of a single moving charge has a “hedgehog” shape V.Voronyuk, V.T.et al.,Phys. Rev. C84, 035202 (2011)

24. Observable No electromagnetic field effects onobservable! V.Voronyuk, V.T.et al.,Phys. Rev. C84, 035202 (2011)

25. CME – charge separation HSD model with/without electromagnetic fields as a CME background does not reproduce the charged pionseparation with respect to the reaction plane => Quark-gluon degrees of freedom ! ? (PHSD model) STAR Collaboration, PRL103, 251601 (2009)

26. Attempts for alternative explanations of a charge separation in relativistic HIC ■F.Wang, Effects of cluster particle correlations on local parity violation observables, Phys. Rev. C81, 064902 (2010). ■ A.Bzdak, V.Koch and J.Liao,Remarks on possible local parity violation in heavy ion collisions, Phys. Rev. C81, 031901 (2010). ■S.Pratt,Alternative contributions to the angular correlations observedat RHIC associated with parity fluctuations,arXiv:1002.1758. ■S.Schlichting and S.Pratt, Explaining angular correlations observed atRHIC with flow and local charge conservation,arXiv:1005.5341. ■S.Schlichting and S.Pratt, Charge conservation at energies available at the BNL Relativistic Heavy Ion Collider and contributions to local parity violation observables, Phys. Rev. C83, 014913 (2011). ■S.Pratt, S.Schlichting and S.Gavin,Effects of momentun conservation and flow on angular correlations,Phys. Rev. C84, 024909 (2011). ■M.Asakawa, A.Majumder and B.Müller,Electric charge separation in strong transient magnetic fields,Phys. Rev. C81, 064912 (2010). ■A.Bzdak, V.Koch and J.Liao, Azimuthal correlations fromtransverse momentum correlations and possible local parity violation, Phys. Rev. C83, 014905 (2011). Really all these hadronic effects are accounted for in the HSD/PHSD model

27. Transverse Momentum Conservation For TMC source (A.Bzdak et al., Phys.Rev. C83, 014905 (2011) )describing pions thermodynamically andmaking use of the central limiting theorem, correlator is For the same-sign correlator and The correlator γij ~ v2!TMC source is not able to explain the observed asymmetry. It is blind to the particle charge. V.T. et al., arXiv:1208.2518

28. The observed correlations are in-plane, contrary to CME expectations !(A.Bzdac, V.Koch, J.Liao, arXiv:0912.5050) In-plane and out-of-plane correlatons STAR, PR C81, 054908 (2010)

29. Compensation effect Δp= δp Transverse momentum increments Δp due to electric and magnetic fields compensate each other !

30. Results of the RHIC BES program STAR Collaboration, J. Phys. G38, 124165 (2011) (√sNN =7.7, 11.5, 39 GeV) Compensation

31. HSD background for BES experiments on CME V.T. et al., Phys.Rev., C85, 034910 (2012) Experiments at 7.7 and 11.5 GeV are explained by HSD, the CME is not seen

32. CME observables in PHSD Partonic scalar part The action of the partonic scalar field on quarks is NOT compensated ! Partonic vector part V.T. et al., arXiv:1208.2518

33. CME observable cos(ψi+ψj) in PHSD G.Gangadharn, J.Phys.G:Nucl.Part.Phys. 38, 124166 (2011)

34. Both in-plane and out-of-plane components needs an additional sizable source of asymmetry rather than only out-of-plane component as expected from CME Charge separation in PHSD V.T. et al., arXiv:1208.2518 PR C86, 014963 (2011) The partonic scalar potential is overestimated in PHSD getting comparable the charge separation with thoseat LHC

35. Conclusions • ●The HSD/PHSD transport model with retarded electromagnetic fields has been developed. • ●The magnetic field and energy density of the deconfined matter reach very high values. • ● Phenomenological analysis predicts disappearance of CME at the energy about the top SPS energy but too small effect at the LHC energy • ● Actual calculations show no noticeable influence of the created electromagnetic fields on observables. It is due to a compensating effect in action of transverse components of electric and magnetic fields on the quasiparticle transport. • ● First low-energy experiments within the RHIC BES program at √sNN = 7.7 and 11.5 GeV can be explained within (pure) hadronic scenario without reference to the spontaneous local CP violation. • ● Direct inclusion of quarks and gluons in evolution (PHSD model) shows that the partonic scalar potential is overestimated. The new source does not dominate in out-of-plane direction as could be expected for the CME but both in-plane and out-of-plane components contribute with a comparable strength (explicit color d.o.f. ?). • ●The CME measurements are still puzzling.