1. The EIC, Heavy Quarks, and QGP Phenomenology W. A. Horowitz University of Cape Town October 4, 2010 6/22/20151EIC at the INT With many thanks to Brian Cole, Miklos Gyulassy, Ulrich Heinz, Jiangyong Jia, and Yuri Kovchegov

2. Two Major Discoveries at RHIC 6/22/2015EIC at the INT2 Huge low-p T v 2 –Described by hydro with low viscosity Huge high-p T suppression –  0 R AA described by pQCD Y. Akiba for the PHENIX collaboration, PLB630, 2005 20-30% Hirano et al., PRC77, 2008

3. Why Are These Interesting? Want to characterize the QGP –Can’t directly measure Use indirect tools Is QGP: –Most perfect fluid ever created/studied? –Can one use strongly and/or weakly coupled field theory methods? pQCD vs. AdS/CFT Enormous influence of geometry 6/22/2015EIC at the INT3

4. Spacetime Evolution of a HI Collision 6/22/2015EIC at the INT4 t = -  t = 0t = 1 fm/ct = 3 fm/c t = +  t = 4 fm/c Initial StateInitial OverlapThermalizationQGP HadronizationHadron Gas At RHIC –Nontrivial to learn about QGP through HIC

5. Geometry and Flow Qualitative picture: Anisotropic initial geometry => anisotropic flow 6/22/2015EIC at the INT5

6. Hydrodynamics and v 2 6/22/2015EIC at the INT6 Hydro –Early therm. –   T   –Equation of State (EOS) –Ideal:  /s = 0 –v 2 : 2 nd Fourier coef of particle spectrum:

7. Viscous Hydrodynamics Viscosity reduces elliptic flow –Naive pQCD =>  /s ~ 1 –Naive AdS/CFT =>  /s ~ 1/4  => Strongly coupled medium? 6/22/2015EIC at the INT7 Luzum and Romatschke, Phys.Rev.C78:034915,2008 Shear Viscosity, Wikipedia

8. Geometry in Viscosity Extraction Poorly constrained initial geom => 100% uncertainty in viscosity –KLN CGC breaks down at edge of nuclear overlap Whole effect comes from edges! Experimental constraints needed! 6/22/2015EIC at the INT8 T Hirano, et al., Phys.Lett.B636:299-304,2006

9. Why High-p T Particles? Tomography in medicine 6/22/2015EIC at the INT9 http://www.fas.org/irp/imint/docs/rst/Intro/P art2_26d.html One can learn a lot from a single probe… PET Scan and even more with multiple probes SPECT-CT Scan uses internal  photons and external X-rays

10. Tomography in QGP Requires well- controlled theory of: –production of rare, high- p T probes g, u, d, s, c, b –in-medium E-loss –hadronization Requires precision measurements of decay fragments 6/22/2015EIC at the INT10 pTpT , , e - Invert attenuation pattern => measure medium properties

11. QGP Energy Loss Learn about E-loss mechanism –Most direct probe of DOF 6/22/2015EIC at the INT11 pQCD Picture AdS/CFT Picture

12. Common variables used are transverse momentum, p T, and angle with respect to the reaction plane,  EIC at the INT12 High-p T Observables Naively: if medium has no effect, then R AA = 1 Fourier expand R AA : 6/22/2015 pTpT , , e -

13. pQCD Rad Picture Bremsstrahlung Radiation –Weakly-coupled plasma Medium organizes into Debye-screened centers –T ~ 250 MeV, g ~ 2  ~ gT ~ 0.5 GeV mfp ~ 1/g 2 T ~ 1 fm R Au ~ 6 fm –1/  << mfp << L mult. coh. em. 6/22/2015EIC at the INT13 –Bethe-Heitler dp T /dt ~ -(T 3 /M q 2 ) p T –LPM dp T /dt ~ -LT 3 log(p T /M q ) Gyulassy, Levai, and Vitev, NPB571 (200)

14. EIC at the INT14 pQCD Success at RHIC: –Consistency: R AA (  )~R AA (  ) –Null Control: R AA (  )~1 –GLV Prediction: Theory~Data for reasonable fixed L~5 fm and dN g /dy~dN  /dy Y. Akiba for the PHENIX collaboration, PLB630, 2005 (circa 2005) 6/22/2015

15. Qualitative Disagreement Mass of quarks should be important –Expect heavy quarks to lose less energy Non-photonic electrons (NPE) surprisingly suppressed –Decay fragments of c and b quarks 6/22/2015UT Colloquium15 Djordjevic,et al. PLB632 (2006) e-e- PHENIX NPE

16. What About Elastic Loss? Appreciable!Finite time effects small 6/22/2015UT Colloquium16 Mustafa, PRC72 (2005)Adil, Gyulassy, WAH, Wicks, PRC75 (2007)

17. pQCD Seemingly Inadequate Lack of qual. simultaneous understanding –  0, ,  R AA well described, BUT –e - R AA, v 2 is not, even with elastic loss 6/22/2015EIC at the INT17 Wicks et al. Death of pQCD at RHIC? pQCD assumes M << E: b E-loss not under control  0 R AA  0 v 2 PHENIX  0 9.5 GeV! 30-40% Centrality WHDG

18. EIC at the INT18 Jets in AdS/CFT Model heavy quark jet energy loss by embedding string in AdS space dp T /dt = -  p T  =    T 2 /2M q J Friess, S Gubser, G Michalogiorgakis, S Pufu, Phys Rev D75 (2007) 6/22/2015 –Similar to Bethe-Heitler dp T /dt ~ -(T 3 /M q 2 ) p T –Very different from LPM dp T /dt ~ -LT 3 log(p T /M q )

19. EIC at the INT19 Compared to Data String drag: qualitative agreement WAH, PhD Thesis 6/22/2015

20. Light Quark and Gluon E-Loss 6/22/2015EIC at the INT20 WAH, in preparation  L g therm ~ E 1/3  L q therm ~ (2E) 1/3 Renk and Marquet, PLB685, 2010

21. High-p T and HIC Spacetime Evolution Jet sees full spacetime evolution –Affected by: Initial geometry Thermalization process E-loss in cold, hadronic matter 6/22/2015EIC at the INT21 t = -  t = 0t = 1 fm/ct = 3 fm/c t = +  t = 4 fm/c Initial StateInitial OverlapThermalizationQGP HadronizationHadron Gas JET

22. Geometry and High-p T v 2 –CGC vs. KLN and rotating RP –Effect not large enough 6/22/2015EIC at the INT22 Effects of geom. on, e.g. v 2, might be quite large WAH and J Jia, in preparation Need experimental constraints on initial geometry!

23. What About Fluctuations? Hot spots can be huge –NEXUS calculation for 10% most central top RHIC energy event For simple E-loss not a large effect –Important for fluc., opacity exp.? 6/22/2015EIC at CUA23 Jia and Wei, arXiv:1005.0645

24. Hydro + Fluctuations Hydro evolution may amplify fluctuations 6/22/2015EIC at CUA24 Gyulassy, Rischke, Zhang, NPA613, 1997

25. Measuring the IC EIC could give experimental handle on initial geometry –Recall e + A diffraction exps. on A at rest 6/22/2015UT Colloquium25 Hahn, Ravenhall, and Hofstadter, Phys Rev 101 (1956)

26. Gluon Distribution of A at x ~ 10 -3 6/22/2015UT Colloquium26 Coherent vector meson production in e + A e’ J/  A’ e A ** Caldwell and Kowalski, PRC 81 (2010) 10 6 J/  Events 2 gluon exchange => mean & correlations Must reject incoherent collisions at ~100% Also DVCS and Incoherent production

27. Importance of Cold Matter E-Loss Large fraction of jet lifetime spent in hadronic matter –QGP lasts ~ 2 fm –Typical jet pathlength ~ 5 fm Measure in EIC 6/22/2015EIC at the INT27 Accardi, QM Italia Accardi et al., Riv.Nuovo Cim.32, 2010

28. Conclusions Tantalizing physics discoveries at RHIC –Large low-p T v 2 nearly perfect strongly coupled fluid (?) –Large high-p T suppression weakly coupled quasiparticle plasma (?) Qualitative understanding of QGP physics requires constraints on full spacetime evolution of HI collision Exciting eA physics opportunities for AA –Knowledge of:  (b), thermalization, cold matter E-loss a qualitative advance of HI via EIC 6/22/2015EIC at the INT28