071026 AdSCFTDay Horowitz

8/11/2019 071026 AdSCFTDay Horowitz

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AdS Strings Intersect with Nuclear Beams at Columbia110/26/07

William Horowitz

Probing AdS/CFT with Heavy Quarks

William HorowitzColumbia University

Frankfurt Institute for Advanced Studies (FIAS)

October 26, 2007

With many thanks to Miklos Gyulassy,Simon Wicks, and Ivan Vitev

arXiv:0706.2336 (LHC predictions)arXiv:0710.0703 (RHIC predictions)


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Introduction

AdS/CFT looks promising, pQCD alsohas its successes

Desire a robust probe that can cleanlyfalsify one or both formalisms:

Try Heavy Quarks!


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William Horowitz

Quantitative AdS/CFT with Jets

Langevin model Collisional energy loss for heavy quarks

Restricted to low pT

pQCD vs. AdS/CFT computation of D, the diffusioncoefficient

ASW model Radiative energy loss model for all parton species

pQCD vs. AdS/CFT computation of

Debate over its predicted magnitude

ST drag calculation

Drag coefficient for a massive quark moving through astrongly coupled SYM plasma at uniform T

not yet used to calculate observables: lets do it!


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Use future detectors identification of c and b todistinguish between pQCD, AdS/CFT

RAA ~ (1-(pT))n(pT), where pf = (1-)pi (i.e. = 1-pf/pi) Asymptotic pQCD momentum loss:

String theory drag momentum loss:

Independent of pT and strongly dependent on Mq!

T2

dependence in exponent makes for a very sensitive probe

Expect: pQCD 0 vs. AdSindep of pT!! dRAA(pT)/dpT > 0 => pQCD; dRAA(pT)/dpT < 0 => ST

rad s L2 log(pT/Mq)/pT

Looking for a Robust, Detectable Signal

ST 1 - Exp(- L), = 1/2 T2/2Mq

S. Gubser, Phys.Rev.D74:126005 (2006); C. Herzog et al.JHEP 0607:013,2006


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Model Inputs for LHC Predictions AdS/CFT Drag: nontrivial mapping of QCD to SYM

Obvious: s = SYM = const., TSYM = TQCD D/2T = 3 inspired: s = .05

pQCD/Hydro inspired: s = .3 (D/2T ~ 1)

Alternative: = 5.5, TSYM = TQCD/31/4

Start loss at thermalization time 0; end loss at Tc

WHDG convolved radiative and elastic energy losss = .3

WHDG radiative energy loss (similar to ASW)

= 40, 100 Use realistic, diffuse medium with Bjorken expansion

PHOBOS (dNg/dy = 1750); KLN model of CGC (dNg/dy = 2900)


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An Enhanced Signal

But what about the interplay betweenmass and momentum?

Take ratio of c to b RAA(pT)

pQCD: Mass effects die out with increasing pT

Ratio starts below 1, asymptotically approaches 1.Approach is slower for higher quenching

ST: drag independent of pT, inverselyproportional to mass. Simple analytic approx.of uniform medium gives

RcbpQCD(pT) ~ nbMc/ncMb ~ Mc/Mb ~ .27 Ratio starts below 1; independent of pT

RcbpQCD(pT) 1 -s n(pT) L2 log(Mb/Mc) ( /pT)


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LHC RcAA

(pT)/Rb

AA(p

T) Prediction

Recall the Zoo:

Taking the ratio cancels most normalization differences seen previously 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 pTWH, M. Gyulassy, nucl-th/0706.2336

WH, M. Gyulassy, nucl-th/0706.2336


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LHC RcAA(pT)/RbAA(pT) Prediction

(with speed limits)

T(0): (O), corrections unlikely for smaller momenta

Tc: (|), corrections likely for higher momenta

WH, M. Gyulassy, nucl-th/0706.2336


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Measurement at RHIC Future detector upgrades will allow for identified c

and b quark measurements

y=0

RHIC

LHC

NOT slowly varying No longer expect

pQCD dRAA/dpT > 0

Large n requirescorrections to nave

Rcb ~ Mc/Mb

RHIC production spectrum significantlyharder than LHC


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RHIC Rcb Ratio

Wider distribution of AdS/CFT curves due to large n:increased sensitivity to input parameters

Advantage of RHIC: lower T => higher AdS speed limits

WH, M. Gyulassy, to be published

pQCD

AdS/CFT

pQCD

AdS/CFT


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071026 AdSCFTDay Horowitz

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