Successes, Failures, and Uncertainties in the Jet Physics of Heavy Ion Collisions - PowerPoint Presentation

Slide1

Successes, Failures, and Uncertainties in the Jet Physics of Heavy Ion Collisions

W. A. HorowitzThe Ohio State UniversityFebruary 23, 2010

16-Nov-10

1

UCT Seminar

With many thanks to Brian Cole,

Miklos

Gyulassy

, Ulrich Heinz, and Yuri

Kovchegov

Slide2

Introduction

What is a heavy ion collision?Why do people care?Phase diagram of QCDBig BangStrongly coupled systemsAdS/CFTWhat is jet physics and what can we learn from it?

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UCT Seminar

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Slide3

Heavy Ion Collisions

Collider machines: RHIC, LHCCartoon of a collision

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UCT Seminar

3

Relativistic Heavy Ion Collider

Large

Hadron

Collider

Slide4

Four Fundamental Forces

16-Nov-10UCT Seminar

4

Gravity

Electromagnetism

Weak

Strong

John

Maarschalk

, travelblog.portfoliocollection.com

starchild.gsfc.nasa.gov

lhs.lps.org/staff/

sputnam

/

chem_notes

/tritium_decay.gif

Slide5

Strong compared to E&M

Electromagnetism

Electric charge (+)

electrons

Carriers: photons

Field theory:

Quantum electro-dynamics (QED)

Strong

Color charge (r, g, b)

quarks

Carriers: gluons

Field theory:

Quantum chromo-dynamics (QCD)

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UCT Seminar

5

+

-

Hydrogen

Look Inside

nobelprize.org

Proton

Slide6

Crucial QCD Facts

Yang-Mills Theory: non-AbelianGluons carry color charge“Strong” over long distances, “weak” over short distancesRigorous analytic calculations only for large momentum processesLarge compared to

LQCD ~ 200 MeVQuarks and gluons are

confinedno bare quark or gluon has ever been detected1,000,000 USD Clay

Millenium prize for proof of confinement in Yang-Mills theories

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UCT Seminar

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Slide7

Standard Model and Phase Diagrams

E&M, Strong, and Weak particle physics well understood (few particles)Many body physics less well understood

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www.sv.vt.edu/classes/MSE2094_NoteBook/96ClassProj/examples/triplpt.html

Water

Hydrogen

Calculated,

Burkhard

Militzer

,

Diploma Thesis, Berlin,

2000

Slide8

Phase Diagram in QCD

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Long Range Plan, 2008

Slide9

Methods of QCD Calculation I: Lattice

All momentaEuclidean correlators

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Long Range Plan, 2008

Kaczmarek

and

Zantow

, PRD71 (2005)

Davies et al. (HPQCD), PRL92 (2004)

Slide10

Methods of QCD Calculation II: pQCD

Any quantitySmall coupling (large momenta only)

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UCT Seminar

10

Jäger

et al., PRD67 (2003)

d’Enterria

, 0902.2011

(

perturbative

QCD)

Slide11

Methods III: AdS/CFT

Maldacena conjecture: SYM in d  IIB in d

+1

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UCT Seminar

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All quantities

N

c

→ ∞

SYM, not QCD

Probably not good approx. for

p+p

; maybe A+A?

Applicable to condensed matter systems?

Gubser

, QM09

Slide12

Why High-pT Jets?

Tomography in medicine16-Nov-10

UCT Seminar

12

http://www.fas.org/irp/imint/docs/rst/Intro/Part2_26d.html

One can learn a lot from

a single probe

…

PET Scan

and even more with multiple probes

SPECT-CT Scan uses internal

g

photons and external X-rays

Slide13

Tomography in QGP

Requires well-controlled theory of:production of rare, high-pT probesg, u, d, s, c, bin-medium E-losshadronization

Requires precision measurements of decay fragments

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p

T

f

,

g

,

e

-

Invert attenuation pattern => measure medium properties

Slide14

QGP Energy Loss

Learn about E-loss mechanismMost direct probe of DOF16-Nov-10

UCT Seminar

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pQCD

Picture

AdS

/CFT Picture

Slide15

pQCD Rad Picture

Bremsstrahlung RadiationWeakly-coupled plasmaMedium organizes into Debye-screened centersT ~ 250

MeV, g ~ 2m ~

gT ~ 0.5 GeVl

mfp ~ 1/g2T ~ 1 fm

R

Au

~ 6 fm

1/

m

<<

l

mfp

<< L

mult

.

coh

.

em.16-Nov-10

UCT Seminar

15

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)

Slide16

Jets in Heavy Ion Collisions

p+pAu+Au

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Y-S Lai, RHIC & AGS Users’ Meeting, 2009

PHENIX

Slide17

UCT Seminar

17High-pT Observable

Naively

: if medium has no effect, then RAA

= 1

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Slide18

UCT Seminar

18pQCD Success at RHIC:

Consistency: R

AA

(

h

)~R

AA

(

p

)

Null Control: R

AA

(

g

)~1

GLV Prediction:

Theory~Data

for reasonable fixed L~5 fm and

dN

g

/

dy~dN

p

/

dy

Y.

Akiba

for the PHENIX collaboration

,

hep

-ex/0510008

(circa 2005)

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Slide19

Qualitative Disagreement

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Djordjevic

,

Gyulassy

, Vogt, and Wicks, PLB632 (2006)

e

-

Slide20

What About Elastic Loss?

Appreciable!Finite time effects small

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Mustafa, PRC72 (2005)

Adil

,

Gyulassy

, WAH, Wicks, PRC75 (2007)

Slide21

UCT Seminar

21Quantitative Disagreement Remains

Pert. at LHC energies?

Wicks, WAH,

Gyulassy

,

Djordjevic

, NPA784 (2007)

16-Nov-10

Slide22

UCT Seminar

22Jets in AdS/CFT

Model heavy quark jet energy loss by embedding string in AdS space

dpT/dt = -

m pT

m

=

pl

1/2

T

2

/2M

q

J

Friess

, S

Gubser

, G

Michalogiorgakis

, S

Pufu

, Phys Rev

D75

(2007)

16-Nov-10

Similar to Bethe-

Heitler

dp

T

/

dt

~ -(T

3

/M

q

2

) pT

Very different from LPM

dp

T

/

dt

~ -LT

3

log(

p

T

/

M

q

)

Slide23

UCT Seminar

23Compared to DataString drag:

qualitative agreement

WAH

,

PhD Thesis

16-Nov-10

Slide24

UCT Seminar

24

pQCD

vs.

AdS/CFT at LHC

Plethora of Predictions:

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

p

T

WAH

, M.

Gyulassy

,

PLB666 (2008)

WAH

, M.

Gyulassy

,

PLB666 (2008)

16-Nov-10

Slide25

UCT Seminar

25Speed limit estimate for applicability of AdS drag

g < gcrit = (1 + 2M

q/l1/2 T)

2 ~ 4Mq2

/(

l

T

2

)

Limited by

M

charm

~ 1.2

GeV

Similar to BH LPM

g

crit ~ M

q/(lT)No Single T for QGP smallest

g

crit

for largest T

T = T(

t

0

, x=y=0): “(”

largest

g

crit

for smallest T

T =

T

c: “]”Not So Fast!

D3 Black Brane

D7 Probe Brane

Q

Worldsheet boundary Spacelike

if

g

>

g

crit

Trailing

String

“Brachistochrone”

“z”

x

5

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UCT Seminar

26

LHC R

cAA(pT)/Rb

AA(pT) Prediction(with speed limits)

T(

t

0

):

“(”

,

corrections

likely small for

smaller

momenta

T

c

:

“]”,

corrections likely

large for

higher

momenta

WAH

, M.

Gyulassy

, PLB666 (2008)

16-Nov-10

Slide27

Conclusions

Heavy Ion Physics is fascinatingJets provide a unique tool for studyUsual theory techniques in quantitative disagreementNew, exciting tool with AdS/CFT, successesExperimental signature:

RcAA/R

bAARecent and future work:

Double ratio at RHICUltimately want to be able to rigorously falsifyUniversality of

AdS

result

Uncertainties in

pQCD

Comparison to additional exp. observables

Corrections to

pQCD

and

AdS

/CFT

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UCT Seminar

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WAH, J.Phys.G35:044025,2008

WAH and Y

Kovchegov

, PLB680:56-61,2009

WAH and B Cole, arXiv:0910.1823 [

hep

-ph]