Heavy Ion Physics at RHIC and LHC W

Heavy Ion Physics at RHIC and LHC W. A. Horowitz The Ohio State University July 16, 2010 With many thanks to Brian Cole, Miklos Gyulassy, Ulrich Heinz, Jiangyong Jia, and Yuri Kovchegov 6/7/2021 UTK 1

QCD: Theory of the Strong Force • Running as – -b-fcn • SU(Nc = 3) PDG ALEPH, PLB 284, (1992) • Nf(E) – Nf(RHIC) ≈ 2. 5 Griffiths Particle Physics 6/7/2021 UTK 2

What are We Interested In? • Measure manybody physics of strong force • Test & understand theory of manybody non-Abelian fields Long Range Plan, 2008 6/7/2021 UTK 3

HI Collisions Tool for Strong Force Physics Study • Want a consistent picture of matter produced in HI collisions – Then, want to quantify the properties of the produced matter 6/7/2021 UTK 4

Spacetime Evolution of a HI Collision • At RHIC t=-¥ t=0 Initial State Initial Overlap t = 1 fm/c Thermalization t = 3 fm/c QGP t=+¥ t = 4 fm/c Hadronization Hadron Gas – Nontrivial to learn about QGP through HIC 6/7/2021 UTK 5

Methods of QCD Calculation I: Lattice Long Range Plan, 2008 • All momenta • Euclidean correlators Kaczmarek and Zantow, PRD 71 (2005) 6/7/2021 Davies et al. (HPQCD), PRL 92 (2004) UTK 6

Methods of QCD Calculation II: p. QCD (perturbative QCD) Jäger et al. , PRD 67 (2003) 6/7/2021 d’Enterria, 0902. 2011 • Any quantity • Small coupling (large momenta only) UTK 7

Methods III: Ad. S/CFT Maldacena conjecture: SYM in d IIB in d+1 Gubser, QM 09 • All quantities • Nc → ∞ SYM, not QCD • Probably not good approx. for p+p; maybe A+A? • Applicable to condensed matter systems? 6/7/2021 UTK 8

Some Probes of the Evolution • Low-p. T leading particle suppressed hadrons q q hadrons leading particle suppressed • High-p. T 6/7/2021 UTK 9

• Hydro A Lil’ Bit of Low-p. T – Early therm. – Evolution: ¶m. Tmn = 0 • “Ideal” – Hadronization • Cooper-Frye freeze-out – Hadronic rescattering T Hirano, et al. , Phys. Rev. C 77: 044909, 2008 6/7/2021 UTK 10

Viscous Hydrodynamics • Viscosity reduces elliptic flow – Naive p. QCD => h/s ~ 1 – Naive Ad. S/CFT => h/s ~ 1/4 p => Strongly coupled medium? 6/7/2021 UTK Luzum and Romatschke, Phys. Rev. C 78: 034915, 2008 11

Geometry Matters • Poorly constrained initial geom => 100% uncertainty in viscosity T Hirano, et al. , Phys. Lett. B 636: 299 -304, 2006 – Fluctuations in IC additional uncon. effect UTK 6/7/2021 12

Why High-p. T Particles? • Tomography in medicine One can learn a lot from a single probe… and even more with multiple probes PET Scan 6/7/2021 http: //www. fas. org/irp/imint/docs/rst/Intro/P art 2_26 d. html UTK SPECT-CT Scan uses internal g photons and external X-rays 13

Tomography in QGP • Requires wellcontrolled theory of: – production of rare, highp. T probes p. T f , g, e- • g, u, d, s, c, b – in-medium E-loss – hadronization Invert attenuation pattern => measure medium properties • Requires precision measurements of decay fragments 6/7/2021 UTK 14

QGP Energy Loss • Learn about E-loss mechanism – Most direct probe of DOF p. QCD Picture Ad. S/CFT Picture 6/7/2021 UTK 15

p. QCD Rad Picture • Bremsstrahlung Radiation – Weakly-coupled plasma • Medium organizes into Debye-screened centers – T ~ 250 Me. V, g ~ 2 • m ~ g. T ~ 0. 5 Ge. V • lmfp ~ 1/g 2 T ~ 1 fm • RAu ~ 6 fm – 1/m << lmfp << L Gyulassy, Levai, and Vitev, NPB 571 (200) • mult. coh. em. – Bethe-Heitler – LPM dp. T/dt ~ -LT 3 log(p. T/Mq) 6/7/2021 UTK dp. T/dt ~ -(T 3/Mq 2) p. T 16

High-p. T Observables Naively: if medium has no effect, then RAA = 1 Common variables used are transverse momentum, p. T, and angle with respect to the reaction plane, f , g, e- f Fourier expand RAA: 6/7/2021 p. T UTK 17

p. QCD Success at RHIC: (circa 2005) Y. Akiba for the PHENIX collaboration, hep-ex/0510008 – Consistency: RAA(h)~RAA(p) – Null Control: RAA(g)~1 – GLV Prediction: Theory~Data for reasonable fixed L~5 fm and d. Ng/dy~d. Np/dy 6/7/2021 UTK 18

Trouble for Rad E-Loss Picture • v 2 • e- e- WAH, Acta Phys. Hung. A 27 (2006) 6/7/2021 Djordjevic, Gyulassy, Vogt, and Wicks, PLB 632 (2006) UTK 19

What About Elastic Loss? • Appreciable! • Finite time effects small Adil, Gyulassy, WAH, Wicks, PRC 75 (2007) Mustafa, PRC 72 (2005) 6/7/2021 UTK 20

p. QCD Still Inadequate • Lack of even qualitative understanding – p 0, h, g RAA well described, BUT – e- RAA, v 2 is not, even with elastic loss PHENIX, Phys. Rev. Lett. 98, 172301 (2007) Wicks et al. • NB: MQ/E << 1 assumed, not well controlled for b 6/7/2021 UTK 21

More Reasons for Concern • Baryon/Meson Ratio • IAA STAR p. QCD w/ DSS p. QCD w/ KKP p. T Jamie Nagle, QM 09 Pert. at LHC energies? – WHDG soon 6/7/2021 WAH, in preparation UTK 22

Death of p. QCD at RHIC? • Failure at > 9 Ge. V! Rui Wei, for PHENIX, QM 09 PHENIX, ar. Xiv: 1006. 3740 6/7/2021 UTK 23

Strongly Coupled Qualitative Successes Ad. S/CFT Blaizot et al. , JHEP 0706 T. Hirano and M. Gyulassy, Nucl. Phys. A 69: 71 -94 (2006) PHENIX, PRL 98, 172301 (2007) 6/7/2021 UTK 24 Betz, Gyulassy, Noronha, Torrieri, PLB 675 (2009)

Jets in Ad. S/CFT • Model heavy quark jet energy loss by embedding string in Ad. S space dp. T/dt = - m p. T m = pl 1/2 T 2/2 Mq – Similar to Bethe-Heitler dp. T/dt ~ -(T 3/Mq 2) p. T J Friess, S Gubser, G Michalogiorgakis, S Pufu, Phys Rev D 75 (2007) – Very different from LPM dp. T/dt ~ -LT 3 log(p. T/Mq) 6/7/2021 UTK 25

Compared to Data • String drag: qualitative agreement WAH, Ph. D Thesis 6/7/2021 UTK 26

Light Quark and Gluon E-Loss WAH, in preparation DLqtherm ~ E 1/3 DLqtherm ~ (2 E)1/3 6/7/2021 UTK 27

p. QCD vs. Ad. S/CFT at LHC • Plethora of Predictions: WAH, M. Gyulassy, PLB 666 (2008) – Taking the ratio cancels most normalization differences – p. QCD ratio asymptotically approaches 1, and more slowly so for increased quenching (until quenching saturates) WAH, M. Gyulassy, PLB 666 (2008) – Ad. S/CFT ratio is flat and many times smaller than p. QCD at only moderate p. T 6/7/2021 UTK 28

Not So Fast! – Speed limit estimate for applicability of Ad. S drag • g < gcrit = (1 + 2 Mq/l 1/2 T)2 ~ 4 Mq 2/(l T 2) – Limited by Mcharm ~ 1. 2 Ge. V • Similar to BH LPM Q Worldsheet boundary Spacelike if g > gcrit x 5 Trailing String “Brachistochrone” – gcrit ~ Mq/(l. T) – No Single T for QGP • smallest gcrit for largest T T = T(t 0, x=y=0): “(” • largest gcrit for smallest T T = Tc: “]” 6/7/2021 D 7 Probe Brane UTK “z” D 3 Black Brane 29

LHC Rc. AA(p. T)/Rb. AA(p. T) Prediction (with speed limits) WAH, M. Gyulassy, PLB 666 (2008) – T(t 0): “(”, corrections likely small for smaller momenta – Tc: “]”, corrections likely large for higher momenta 6/7/2021 UTK 30

RHIC Rcb Ratio p. QCD Ad. S/CFT WAH, M. Gyulassy, JPhys. G 35 (2008) • Wider distribution of Ad. S/CFT curves due to large n: increased sensitivity to input parameters • Advantage of RHIC: lower T => higher Ad. S speed limits 6/7/2021 UTK 31

Conclusions • RHIC at 10 Years – Fascinating discoveries • Perfect (? ) Fluidity • “Jet” Suppression • Full Picture Lacking – Little constrains many aspects of HIC • Initial geometry • Thermalization • Energy loss mechanism • Exciting Days Ahead – New Energy Regime at LHC • Hydro confirmation? • New tests for E-loss – HF Separation at RHIC 6/7/2021 UTK 32