2/7/09 william horowitz high-p t physics at lhc1 testing ads/cft at lhc william horowitz the ohio...

High-pT Physics at LHC 12/7/09

William Horowitz

Testing AdS/CFT at LHC

William HorowitzThe Ohio State University

February 6, 2009

With many thanks to Yuri Kovchegov and Ulrich Heinz


William Horowitz

First, a Perturbative Detour


William Horowitz

pQCD Success in High-pT at RHIC:

– Consistency: RAA()~RAA()

– Null Control: RAA()~1

– GLV Calculation: Theory~Data for reasonable fixed L~5 fm and dNg/dy~dN/dy• Assuming pQCD E-loss, let’s clear up some myths

Y. Akiba for the PHENIX collaboration, hep-ex/0510008

(circa 2005)


William Horowitz

Surface Emission: Red Herring?

• If you believe in pQCD E-loss, observed jets come from deep in the medium

T. Renk and K. J. Eskola, PoS LHC07, 032 (2007)

S. Wicks, et al., Nucl. Phys. A784, 426 (2007)

HT, AMY, ASW WHDG BDMPS + Hydro

S. A. Bass, et al., arXiv:0808.0908 [nucl-th].


William Horowitz

Fragility is Fragile

• Linear-linear plot of RAA(qhat) is the incorrect way to think about the problem

PHENIX, Phys. Rev. C77, 064907 (2008)

K. J. Eskola, et al., Nucl. Phys. A747, 511 (2005)


William Horowitz

Fragility is Fragile (cont’d)

• If you believe in pQCD E-loss, RAA is NOT a fragile probe of the medium– Linear on a log-log plot

– Double => halve RAA

– Similar results for WHDG, GLV, AMY, ZOWW, etc.

PHENIX, Phys. Rev. C77, 064907 (2008)


William Horowitz

Quantitative Extraction

• Model params to within ~20%– Experimental error only!!

• Sys. theor. err. could be quite large– Running coupling uncertainties

» Smaller at LHC?

– Multi-gluon correlations?» Larger at LHC?

– Handling of geometry– …

• See also TECHQM wiki: S. Wicks, et al., Nucl. Phys. A783, 493 (2007)https://wiki.bnl.gov/TECHQM/index.php/WHDG

PHENIX, PRC77, 064907 (2008)


William Horowitz

Trouble for High-pT wQGP Picture– v2 too small – NPE supp. too large

STAR, Phys. Rev. Lett. 98, 192301 (2007)

0 v2

M Tannenbaum, High-pT Physics at LHC ‘09

PHENIX, Phys. Rev. Lett. 98, 172301 (2007)

NPE v2

Pert. at LHC energies?


William Horowitz

Back to the Future Fifth Dimension


William Horowitz

Motivation for High-pT AdS• Why study AdS E-loss models?

– Many calculations vastly simpler• Complicated in unusual ways

– Data difficult to reconcile with pQCD– pQCD quasiparticle picture leads to

dominant q ~ ~ .5 GeV mom. transfers=> Nonperturbatively large s

• Use data to learn about E-loss mechanism, plasma properties– Domains of self-consistency crucial

for understanding


William Horowitz

Strong Coupling Calculation

• The supergravity double conjecture:

QCD SYM IIB

– IF super Yang-Mills (SYM) is not too different from QCD, &

– IF Maldacena conjecture is true– Then a tool exists to calculate

strongly-coupled QCD in SUGRA


William Horowitz

AdS/CFT Energy Loss Models– Langevin Diffusion

• Collisional energy loss for heavy quarks• Restricted to low pT

• pQCD vs. AdS/CFT computation of D, the diffusion coefficient

– ASW/LRW model• Radiative energy loss model for all parton species• pQCD vs. AdS/CFT computation of• Debate over its predicted magnitude

– Heavy Quark Drag calculation• Embed string representing HQ into AdS geometry• Includes all E-loss modes• Empty space calculation:• Previously: thermalized QGP plasma, temp. T,

crit<~Mq/T

Moore and Teaney, Phys.Rev.C71:064904,2005Casalderrey-Solana and Teaney, Phys.Rev.D74:085012,2006; JHEP 0704:039,2007

BDMPS, Nucl.Phys.B484:265-282,1997Armesto, Salgado, and Wiedemann, Phys. Rev. D69 (2004) 114003Liu, Ragagopal, Wiedemann, PRL 97:182301,2006; JHEP 0703:066,2007

Gubser, Phys.Rev.D74:126005,2006Herzog, Karch, Kovtun, Kozcaz, Yaffe, JHEP 0607:013,2006

Kharzeev, arXiv:0806.0358 [hep-ph]


William Horowitz

Energy Loss Comparison

– AdS/CFT Drag:dpT/dt ~ -(T2/Mq) pT

– Similar to Bethe-HeitlerdpT/dt ~ -(T3/Mq

2) pT

– Very different from LPMdpT/dt ~ -LT3 log(pT/Mq)

tx

Q, m v

D7 Probe Brane

D3 Black Brane(horizon)

3+1D Brane Boundary

Black Holez =

zh = 1/T

zm = 1/2/2m

z = 0


William Horowitz

RAA Approximation

– Above a few GeV, quark production spectrum is approximately power law:• dN/dpT ~ 1/pT

(n+1), where n(pT) has some momentum dependence

– We can approximate RAA(pT):

• RAA ~ (1-(pT))n(pT),

where pf = (1-)pi (i.e. = 1-pf/pi)

y=0

RHIC

LHC


William Horowitz

– Use LHC’s large pT reach and identification of c and b to distinguish between pQCD, AdS/CFT• 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. AdS indep 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), = T2/2Mq

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


William Horowitz

Model Inputs– 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 loss• s = .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)


William Horowitz

– LHC Prediction Zoo: What a Mess!– Let’s go through step by step

– Unfortunately, large suppression pQCD similar to AdS/CFT– Large suppression leads to flattening– Use of realistic geometry and Bjorken expansion allows saturation below .2– Significant rise in RAA(pT) for pQCD Rad+El– Naïve expectations met in full numerical calculation: dRAA(pT)/dpT > 0 => pQCD; dRAA(pT)/dpT < 0 => ST

LHC c, b RAA pT Dependence

WH and M. Gyulassy, Phys. Lett. B 666, 320 (2008)


William Horowitz

• But what about the interplay between mass 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, inversely proportional to mass. Simple analytic approx. of uniform medium gives

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

An Enhanced Signal

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


William Horowitz

LHC RcAA(pT)/Rb

AA(pT) 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 pT

– Distinguish rad and el contributions?WH and M. Gyulassy, Phys. Lett. B 666, 320 (2008)



William Horowitz

Additional Discerning Power

– Adil-Vitev in-medium fragmentation rapidly approaches, and then broaches, 1» Does not include partonic E-loss, which will be nonnegligable as ratio goes to unity

– Higgs (non)mechanism => Rc/Rb ~ 1 ind. of pT

– Consider ratio for ALICE pT reachmc = mb = 0


William Horowitz

• Speed limit estimate for applicability of AdS drag– < crit = (1 + 2Mq/1/2 T)2

~ 4Mq2/(T2)

• Limited by Mcharm ~ 1.2 GeV

• Similar to BH LPM– crit ~ Mq/(T)

• No single T for QGP

Not So Fast!Q D7 Probe Brane

Worldsheet boundary Spacelikeif > crit

TrailingString

“Brachistochrone”

z

x

D3 Black Brane


William Horowitz

LHC RcAA(pT)/Rb

AA(pT) Prediction(with speed limits)

– T(0): (, highest T—corrections unlikely for smaller momenta

– Tc: ], lowest T—corrections likely for higher momenta



William Horowitz

Derivation of BH Speed Limit I

• Constant HQ velocity– Assume const. v kept by F.v

– Critical field strength Ec = M2/½

• E > Ec: Schwinger pair prod.

• Limits < c ~ T2/M2

– Alleviated by allowing var. v• Drag similar to const. v

z = 0

zM = ½ / 2M

zh = 1/T

EF.v = dp/dt

dp/dt

Q

Minkowski Boundary

D7

D3

v

J. Casalderrey-Solana and D. Teaney, JHEP 0704, 039 (2007)

Herzog, Karch, Kovtun, Kozcaz, Yaffe, JHEP 0607:013 (2006)z =


William Horowitz

Derivation of BH Speed Limit II• Local speed of light

– BH Metric => varies with depth z• v(z)2 < 1 – (z/zh)4

– HQ located at zM = ½/2M

– Limits < c ~ T2/M2

• Same limit as from const. v

– Mass a strange beast• Mtherm < Mrest

• Mrest Mkin

– Note that M >> T

z = 0

zM = ½ / 2M

zh = 1/T

EF.v = dp/dt

dp/dt

Q

Minkowski Boundary

D7

D3

v

S. S. Gubser, Nucl. Phys. B 790, 175 (2008)

z =


William Horowitz

Universality and Applicability

• How universal are drag results?– Examine different theories– Investigate alternate geometries

• When does the calculation break down?– Depends on the geometry used


William Horowitz

New Geometries

Albacete, Kovchegov, Taliotis,JHEP 0807, 074 (2008)

J Friess, et al., PRD75:106003, 2007

Constant T Thermal Black Brane

Shock GeometriesNucleus as Shock

Embedded String in Shock

DIS

Q

vshock

x

zvshock

x

zQ

Before After

Bjorken-Expanding Medium


William Horowitz

Shocking Motivation

• Warm-up for full Bjorken metricR. A. Janik and R. B. Peschanski, Phys. Rev. D 73, 045013 (2006)

• No local speed of light limit!– Metric yields -1 < v < 1– In principle, applicable to all quark masses

for all momenta– Subtlety in exchange of limits?


William Horowitz

Standard Method of Attack• Parameterize string worldsheet

– X(, )

• Plug into Nambu-Goto action

• Varying SNG yields EOM for X

• Canonical momentum flow (in , )


William Horowitz

Shock Geometry Results• Three t-ind. solutions (static gauge):

X = (t, x(z), 0,0, z)

– x(z) = c, ± ½ z3/3

• Constant solution unstable• Time-reversed negative x solution unphysical• Sim. to x ~ z3/3, z << 1, for const. T BH

geom.

½ z3/3 ½ z3/3

c

vshock

Qz = 0

z = x


William Horowitz

HQ Momentum Loss in the Shock

Relate to nuclear properties– Use AdS dictionary: ~ T--/Nc

2

– T-- = (boosted den. of scatterers) x (mom.)

– T-- = Nc2 (3 p+/) x (p+)

• Nc2 gluons per nucleon in shock

• is typical mom. scale; typical dist. scale• p+: mom. of shock gluons as seen by HQ• p: mom. of HQ as seen by shock

=> = 2p+2

x(z) = ½ z3/3 =>


William Horowitz

HQ Drag in the Shock• HQ Rest Frame • Shock Rest Frame

vshMq

1/

vq = -vsh

Mq

i i vsh = 0vq = 0

–Recall for BH:–Shock gives exactly the same drag as BH for = T


William Horowitz

Conclusions and Outlook for

• the LHC Experiment:– Use data to test E-loss mechanism

• RcAA(pT)/Rb

AA(pT) wonderful tool

– p+Pb and Direct- Pb+Pb critical null controls

• the AdS Drag:– Applicability and universality crucial

• Both investigated in shock geom.

– Shock geometry reproduces BH momentum loss

• Unrestricted in momentum reach• Variable velocity case nontrivial

– Future work• Time-dependent shock treatment• AdS E-loss in Bjorken expanding medium


William Horowitz

Backup Slides


William Horowitz

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 requires corrections to naïve

Rcb ~ Mc/Mb

– RHIC production spectrum significantly harder than LHC


William Horowitz

RHIC c, b RAA pT Dependence

• Large increase in n(pT) overcomes reduction in E-loss and makes pQCD dRAA/dpT < 0, as well

WH, M. Gyulassy, arXiv:0710.0703 [nucl-th]


William Horowitz

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, arXiv:0710.0703 [nucl-th]

pQCD

AdS/CFT

pQCD

AdS/CFT


William Horowitz

Simultaneous , e- Suppression

• pQCD is not falsified:– Elastic loss?– Uncertainty in c, b

contributions– In-medium

fragmentation?– Resonances?

S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076A. Adil and I. Vitev, hep-ph/0611109

H. Van Hees, V. Greco, and R. Rapp, Phys. Rev. C73, 034913 (2006)

• Naïve pQCD => large mass, small loss

• But , RAA ~ e- RAA!


William Horowitz

Zooming In

– Factor ~2-3 increase in ratio for pQCD

– Possible distinction for Rad only vs. Rad+El at low-pT


William Horowitz

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

• Consider ratio for ALICE pT reach


William Horowitz

• Consider ratio for ALICE pT reach


William Horowitz

LHC Predictions

WH, S. Wicks, M. Gyulassy, M. Djordjevic, in preparation

• Our predictions show a significant increase in RAA as a function of pT

• This rise is robust over the range of predicted dNg/dy for the LHC that we used

• This should be compared to the flat in pT curves of AWS-based energy loss (next slide)

• We wish to understand the origin of this difference


William Horowitz

Curves of ASW-based energy loss are flat in pT

K. J. Eskola, H. Honkanen, C. A. Salgado, and U. A. Wiedemann, Nucl. Phys. A747:511:529 (2005)

A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005)

(a) (b)

Comparison of LHC Predictions


William Horowitz

Why ASW is Flat• Flat in pT curves result from extreme suppression at

the LHC – When probability leakage P( > 1) is large, the (renormalized or

not) distribution becomes insensitive to the details of energy loss

• Enormous suppression due to:– Already (nonperturbatively) large suppression at RHIC for ASW– Extrapolation to LHC assumes 7 times RHIC medium densities

(using EKRT)» Note: even if LHC is only ~ 2-3 times RHIC, still an immoderate ~ 30-

45

• As seen on the previous slide, Vitev predicted a similar rise in RAA(pT) as we do

– Vitev used only radiative loss, Prad(), but assumed fixed path

– WHDG similar because elastic and path fluctuations compensate


William Horowitz

Elastic Can’t be Neglected!

M. Mustafa, Phys. Rev. C72:014905 (2005) S. Wicks, WH, M. Gyulassy, and M. Djordjevic, nucl-th/0512076


William Horowitz

Elastic Remains Important


William Horowitz

A Closer Look at PQM

– Difficult to draw conclusions on inherent surface bias in PQM from this for three reasons: • No Bjorken expansion• Glue and light quark

contributions not disentangled

• Plotted against Linput (complicated mapping from Linput to physical distance)

A. Dainese, C. Loizides, G. Paic, Eur. Phys. J. C38:461-474 (2005)


William Horowitz

Direct : A+A IS Well Understood

PHENIX, Phys. Rev. Lett. 94, 232301 (2005)


William Horowitz

More Geometry• pT dependence of

surface bias• Nontrivial a posteriori

fixed length dependence

S. Wicks, WH, M. Djordjevic and M. Gyulassy, Nucl. Phys. A784, 426 (2007)

(not surface emission!)

S. A. Bass, et al., arXiv:0808.0908 [nucl-th].

2/7/09 william horowitz high-p t physics at lhc1 testing ads/cft at lhc william horowitz the ohio...

Documents

highp t ads

highp t wqgp picture

low p t pqcd

lhc william horowitz

pqcd eloss

dimension slide

sugra slide

eloss mechanism