RHIC Challenges and LHC Outlook W. A. Horowitz The Ohio State University June 21, 2010 With many thanks to Brian Cole, Miklos Gyulassy, Ulrich Heinz, Jiangyong Jia, and Yuri Kovchegov 11/13/2018 INT Workshop 2010

QCD: Theory of the Strong Force ALEPH, PLB284, (1992) PDG Running as -b-fcn SU(Nc = 3) Nf(E) Nf(RHIC) ≈ 2.5 Griffiths Particle Physics 11/13/2018 Wayne State University Seminar

Success of pQCD in p+p Calibrated probe in p+p Note need for NLO for production d’Enterria, 0902.2011 11/13/2018 INT Workshop 2010

Why High-pT Particles in HI? Tomography in medicine One can learn a lot from a single probe… and even more with multiple probes SPECT-CT Scan uses internal g photons and external X-rays PET Scan http://www.fas.org/irp/imint/docs/rst/Intro/Part2_26d.html 11/13/2018 INT Workshop 2010

Tomography in QGP Indep. check of hydro geom. meas. vital for quant. h/s Requires well-controlled theory of: production of rare, high-pT probes g, u, d, s, c, b in-medium E-loss hadronization Requires precision measurements of decay fragments pT f , g, e- Invert attenuation pattern => measure medium properties 11/13/2018 INT Workshop 2010

QGP Energy Loss Learn about E-loss mechanism Most direct probe of DOF AdS/CFT Picture pQCD Picture p h g p e- 11/13/2018 INT Workshop 2010

pQCD Success at RHIC: (circa 2005) Null Control: RAA(g)~1 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 dNg/dy~dNp/dy 11/13/2018 INT Workshop 2010

Irony of Multiple Observables (I) v2 too small NPE supp. too large p0 v2 C. Vale, QM09 Plenary (analysis by R. Wei) WHDG Wicks, WAH, Gyulassy, Djordjevic, NPA784 (2007) NPE v2 PHENIX, Phys. Rev. Lett. 98, 172301 (2007) 11/13/2018 INT Workshop 2010

Irony of Multiple Observables (II) IAA WHDG soon Baryon/Meson Ratio STAR pT pQCD w/ KKP pQCD w/ DSS WAH, in preparation Jamie Nagle, QM09 Pert. at LHC energies? 11/13/2018 INT Workshop 2010

Experimental Convergence on NPE c/b production ~ FONLL predictions Large b contribution STAR & PHENIX now consistent in p+p RAA? Bertrand Biritz, QM09 Wei Xie, DIS10 11/13/2018 INT Workshop 2010

Need for pQCD Theory Improvement NB: pQCD calculations so far assume M << E b corrections likely large c and b separation Success of AdS/CFT? dpT/dt = - m pT m = pl1/2 T2/2Mq WAH, PhD Thesis 11/13/2018 INT Workshop 2010

v2 Marches On Data improves, pQCD falsified to higher pT Does v2 becomes constant, >> pQCD? Rui Wei, for PHENIX, QM09 11/13/2018 INT Workshop 2010

v2 Comparison to WHDG Failure at > 9 GeV! Future: improve density scaling pred. WS Glauber HN Mixed KLN CGC 2008 PHOBOS NB: KLN CGC and Hirano/Nara tuned to old (2002) PHOBOS data Horowitz and Jia, in preparation 11/13/2018 J Jia, JET Collab Meeting INT Workshop 2010

Decreasing the Disagreement How much can we sharpen the medium? Use CGC IC Include initial state fluctuations Correct mismatch between reaction plane and participant plane Horowitz and Jia, in preparation 11/13/2018 INT Workshop 2010

pQCD L1-2 Seemingly Not Enough CGC, fluctuations not enough for pQCD AdS/CFT: DE ~ L3 Better job? 20-30% PHENIX p0 Glauber CGC Solid: analytic Dashed: fluctuating WAH and J Jia, in preparation Marquet and Renk, PLB685 (2010) Largest medium density w/i unc. from RAA 11/13/2018 INT Workshop 2010

Theoretical Uncertainties: Different Formalisms, Different Results Very diff. ideas about relevant physics pQCD AMY, BDMPS, GLV, HT Is this a systematic th. unc.? Can we falsify? Bass et al., Phys.Rev.C79: 024901,2009 What about AdS/CFT? 11/13/2018 INT Workshop 2010

Mechanics of Energy Loss RAA ~ ∫(1-ϵ)n P(ϵ) dϵ pf = (1-ϵ)pi Opacity expansions finds single inclusive gluon emission spectrum dNg/dxdkTdqT 11/13/2018 INT Workshop 2010

Poisson Convolution Find P(ϵ) by convolving dNg/dx Approximates probabilistic multiple gluon emission, Sudakov assume independent emissions NB: ϵ is a momentum fraction Gyulassy, Levai, and Vitev NPB594 (2001) 11/13/2018 INT Workshop 2010

Opacity Expansion Calculation Want to find dNg/dx Make approximations to simplify derivation Small angle emission: kT << xE Note: ALL current formalisms use collinear approximation Derived dNg/dxdkT violates collinear approx Both IR and UV safe Enforce small angle emission through UV cutoff in kT 11/13/2018 INT Workshop 2010

Uncertainty from Collinear Approx Derived dNg/dxdkT maximally violates collinear approximation WAH and B Cole, PRC81, 2010 dNg/dx depends sensitively on kT cutoff Despite UV safety For effect on extracted prop., must understand x 11/13/2018 INT Workshop 2010

Two Standard x Definitions ASW-SH: xE Energy fraction GLV: x+ Plus momentum fraction P NB: gluon always on-shell 11/13/2018 INT Workshop 2010

Coordinate Transformations Same in the limit kT/xE → 0! UV cutoff given by restricting maximum angle of emission Previous comparisons with data took qmax=p/2 Vary qmax to estimate systematic theoretical uncertainty P q 11/13/2018 INT Workshop 2010

Jacobians ϵ is fraction of longitudinal momentum Need dNg/dxE to find P(ϵ) A Jacobian is required for x = x+ interpretation 11/13/2018 INT Workshop 2010

Rad. Gluon Kin. Sensitivities UV What about IR? WAH and B Cole, PRC81, 2010 11/13/2018 INT Workshop 2010

Collinearity and Gluon Mass Massless gluons: Large IR cutoff sensitivity Gluons with thermal mass ~ BDMS, JHEP 0109 (2001) Larger x better respects kT << xE 11/13/2018 INT Workshop 2010 WAH and B Cole, PRC81, 2010

Results Quantitatively compare to PHENIX data Assumed infinite Elastic precision WAH and B Cole, PRC81, 2010 11/13/2018 INT Workshop 2010

Parton Energy Dependence Dependence on parton energy Uncertainty on qhat Assume all formalisms equally affected WAH and B Cole, PRC81, 2010 11/13/2018 INT Workshop 2010

JET Collaboration Meeting at LBL v2: “Collinearly Safe” Fix dNg/dy from RAA, calculate v2 Expect larger v2 for smaller opening angle ( tcoh ~ 1/kT2 ) IAA: coming soon Rad Only Rad + El v2 pT 20-30% p0 20-30% p0 v2 pT Data Data WAH, in preparation 11/13/2018 JET Collaboration Meeting at LBL

LHC Predictions Elastic still significant at LHC energies LHC: Power of power law of production more constant RHIC LHC Power v2 still too small at LHC? 11/13/2018 INT Workshop 2010

Need for Null Control Jets at LHC? T Isobe, JPhysG34 (2007) 11/13/2018 INT Workshop 2010

WHDG LHC Predictions As shown in QM’06 Large rise for WHDG DE/E ~ Log(E)/E, dies faster than power increases Note that ASW & PQM used EKRT extrapolation with dNg/dy ~ 7000 11/13/2018 INT Workshop 2010

“PHENIX Extrapolation” Flat out to infinity PHENIX PRC77 11/13/2018 INT Workshop 2010

Heavy Quark Probes in AdS/CFT Model heavy quark energy loss by embedding string in AdS space dpT/dt = - m pT m = pl1/2 T2/2Mq J Friess, S Gubser, G Michalogiorgakis, S Pufu, Phys Rev D75 (2007) Similar to Bethe-Heitler dpT/dt ~ -(T3/Mq2) pT Very different from LPM dpT/dt ~ -LT3 log(pT/Mq) 11/13/2018 INT Workshop 2010

pQCD vs. AdS/CFT at LHC Plethora of Predictions: WAH, M. Gyulassy, PLB666 (2008) Taking the ratio cancels most normalization differences pQCD ratio asymptotically approaches 1, and more slowly so for increased quenching (until quenching saturates) AdS/CFT ratio is flat and many times smaller than pQCD at only moderate pT WAH, M. Gyulassy, PLB666 (2008) 11/13/2018 INT Workshop 2010

Worldsheet boundary Spacelike if g > gcrit Not So Fast! Speed limit estimate for applicability of AdS drag g < gcrit = (1 + 2Mq/l1/2 T)2 ~ 4Mq2/(l T2) Limited by Mcharm ~ 1.2 GeV Similar to BH LPM gcrit ~ Mq/(lT) No Single T for QGP smallest gcrit for largest T T = T(t0, x=y=0): “(” largest gcrit for smallest T T = Tc: “]” D3 Black Brane D7 Probe Brane Q Worldsheet boundary Spacelike if g > gcrit Trailing String “Brachistochrone” “z” x5 11/13/2018 INT Workshop 2010

LHC RcAA(pT)/RbAA(pT) Prediction (with speed limits) WAH, M. Gyulassy, PLB666 (2008) T(t0): “(”, corrections likely small for smaller momenta Tc: “]”, corrections likely large for higher momenta 11/13/2018 INT Workshop 2010

Additional Discerning Power Adil-Vitev in-medium fragmentation rapidly approaches, and then broaches, 1 Does not include partonic energy loss, which will be nonnegligable as ratio goes to unity CERN Heavy Ion Forum

RHIC Rcb Ratio pQCD pQCD AdS/CFT AdS/CFT WAH, M. Gyulassy, JPhysG35 (2008) Wider distribution of AdS/CFT curves due to large n: increased sensitivity to input parameters Advantage of RHIC: lower T => higher AdS speed limits 11/13/2018 INT Workshop 2010

Conclusions pQCD is in trouble in A+A at RHIC v2 is just too large, out to > 9 Gev! Large sys. th. unc. from large angle radiation Problem remains for higher orders in opacity, dyn. sc. cent. Despite unc. in RAA, global analysis yields small unc. for v2 More calculated obs. on the way Saved by NLO, better geom, better elastic, fewer approx.? NPE: need c and b sep. & need MQ ~ E theory AdS applied to jets tantalizing Exciting days to come at LHC pQCD vs. AdS Drag vs. In-medium diss. Need detailed estimates of unc. for falsification (global analysis) Will need null control 11/13/2018 INT Workshop 2010