Charles Gale McGill Hard Probes 2004 In-medium effects on electromagnetic probes Hard Probes 2004 International Conference on Hard and Electromagnetic

Hard Probes 2004 Charles Gale

McGill

In-medium effects on electromagnetic probes

Hard Probes 2004

International Conference onHard and Electromagnetic Probes of High Energy Nuclear Collisions


McGill

In-medium: what medium?

DOE/NSF NSACLong Range Plan

UrQMD

Phase-space trajectory goes through qualitatively different media


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The information carried by EM radiation

i

fk 2| |fi

fi

SR

V

4 ˆ| ( ) ( ) |fiS f d x J x A x i [photons]

4 4 ˆ| ( ) ( ) ( ) |efiS f d xd yJ x D x y J y i

[dileptons]

4(2 ) ( ) ( )2

ˆ ˆ| | | |

fi i f i f

gR P k P P k P

V

f J i i J f

[photons]

absorption emission


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Info carried out, II

i

j

K

i K

j

e

e

Thermal rates: avg over initial

states & sum over final

34

3

1(2 ) ( )

2 (2 )

ˆ ˆ| | | |

iKi f

i f

g d kdR e p p k

Z

j J i i J f

Thermal ensemble average of the current-current correlation function


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Info, III

4

,

1( ) (2 ) ( )

ˆ ˆ| | | |

iKi f

i f

f k e p p kZ

f J i i J f

Isolate the correlation

Function:

Spectral representation

2( ) Im ( )

( 1)Rf k k

e

A direct connection to the in-medium photon self-energy


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Info, IV

3

3 3

1Im ( )

(2 ) 1

d R gk

d k e

Emission rates:

[photons]

6 2

3 3 6 4

2 1 1Im ( )

(2 ) 1

d R eE E L k

d p d p k e

[dileptons]

2( )lL p p p p g p p m


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Info, V

A model for the hadronic electromagnetic current: VMD

2 2 2e e eJ m m m

g g g

The current-field identity(J. J. Sakurai)

Im Im ImVMD

TT TJ J D Spectral density

The photon/dilepton signal can tell us about the in-medium

spectral densities of vector mesons


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Vector Meson Spectral Densities: A Sample Calculation I

Ralf Rapp and Charles Gale, Phys. Rev. C 60, 024003 (1999)


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The interaction is constrained by basic hadronic phenomenology

Chiral U(3)L x U(3)R Massive Yang-Mills:

2 † 2 †

2 L0

1 1Tr Tr M U + U

8 81

Tr Tr2non-minimal terms

L L R R L R R

F D UD U F

F F F F m A A A A

L

Parameters and form factors are constrained by hadronic phenomenology:•Masses & strong decay widths•Electromagnetic decay widths•Other hadronic observables:

• e.g. 1 /a D S


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Vector Meson Spectral Densities

The spectral density is flattened

and broadened


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Vector Meson Spectral Densities, IV(adding baryons)

R. Rapp & Wambach, 1999


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Vector spectral densities from data

c.m.c.m.

c.m.

1 exp( )1( )

12 4 sin2

P

apR a PR

a aRP

R R

q r if s W s

q sM s i

3c.m.

3( , ) 4 ( ) ( )

(2 )a a a

d k sE p n k f s

•Should hold near the mass-shell•Adler decoupling enforced

E. V.Shuryak, Nucl. Phys. A 533, 761 (1991); V. L. Eletsky and V. L.Ioffe, Phys. Lett. B 401, 327 (1997); Eletsky, Belkacem, Ellis, Kapusta,Phys. Rev. C 64, 035202 (2001)


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Two approaches:

•Rates are also constrained by nuclear photoabsorption data•Mass shifts & broadening are related by dispersion relations

Rapp & WambachEletsky, Ioffe, Kapusta


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Vector Meson Spectral Densities, VI

V. Eletsky, et al., PRC 2001 Teodorescu, Dutt-Mazumder, Gale, PRC 2002


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Fold in With a Dynamical Evolution Model

Huovinen et al., 2002

What’s new? Photons…


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The intermediate mass sector

• Direct connection to Hard Probes• Off-shell effects are potentially important for

effective hadronic interactions Gao & Gale, PRC 57, 254 (1998)

• A lot of data already exists!

DD_

DY

NA50Pb-Pb 158 GeV

central collisions

charm DY


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e+ e- Data: A Wealth of Information

• OLYA

• CMD

• DM-1(2)

• ARGUS

• M3N

•


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2 2

12

4( / ) ( ) ( ) ( )

2 2em VdR

MT K M T M M MdM

I. Kvasnikova, C. Gale, and D. K. Srivastava, PRC 65, 064903 (2002)

Z. Huang, PL B361, 131 (1995)


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A larger comparison

Agreement across approaches


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Li and Gale, PRC (1998)

Intermediate mass data

A. L. S. Angelis et al. (Helios 3), Eur. Phys. J. (1998)

R. Rapp & E. Shuryak, PLB (2000)


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NA50 Data (cont’nd)

I. Kvasnikova, C. Gale, and

D. K. Srivastava, PRC 2002

•In agreement with multiplicity dependence•Includes detector acceptance & efficiency

(O. Drapier, NA50)


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Intermediate masses: partial summary

• Agreement across models: thermal dileptons are seen

• Case for charm enhancement: weak

• QGP: at most 15-20%

• DY? (J. Qiu)

• NA60


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Electromagnetic radiation from the partonic sector

“Basic” approaches

McLerran, Toimela (1986); Kajantie, Kapusta, McLerran, Mekjian (1986)Baier, Pire, Schiff (1988); Altherr, Ruuskanen (1992)

Rates diverge: 2ln( / 0)s T q

HTLresummation


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• HTL program: Klimov (1981), Weldon (1982)

Braaten & Pisarski (1990); Frenkel & Taylor (1990)

2Im lnR

th

T

m gT

Kapusta, Lichard, Seibert (1991)Baier, Nakkagawa, Niegawa, Redlich (1992)

Going to two loops: Aurenche, Kobes, Gelis, Petitgirard (1996) Aurenche, Gelis, Kobes, Zaraket (1998)

Co-linear singularities:2

2s sth

T

m


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Singularities can be re-summed

Arnold, Moore, and Yaffe

JHEP 12, 009 (2001); JHEP 11, 057 (2001)

• Incorporates LPM

• Complete leading order in S

• Inclusive treatment of collinear enhancement, photon and gluon

emission

Can be expressed in terms of the solution to a linear integral equation


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How big (small) is this?

PhenomenologicalExploration…

Turbide, Rapp & Gale (2004)


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Photons?

Sinha & Srivastava, 2001 Huovinen et al., 2002

No baryons


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• Same spectral densities as low mass dileptons• Same dynamical model; same boundary conditions• Cronin contribution estimated from pA data (E629, NA3)• QGP: small

Turbide, Rapp & GalePRC 2004


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WA98: new analysis

Low pT spectrum sensitive to thepion-pion cross section in the

scalar-scalar channel: Chiral symmetry?

Turbide, Rapp & Gale, in preparation


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@ RHIC

• There is a window

Turbide, Rapp & Gale PRC (2004)


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–Isospin mixing–G-parity violation

Exotica? (squeezing dileptons out of broken symmetries, part I)

• Medium-induced symmetry breaking:– Lorentz symmetry scalar-vector mixing

0 ,a

( )S. A. Chin (1977); A. Weldon (1992); Saito, Tsushima, Thomas, Williams (1998); Wolf, Friman, Soyeur (1998)

:


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Mixing Enables a Hybrid Correlator

• Vanishes in vacuum

• Non-zero in matter

4 . . { ( ) (0)} . .iq x V Sd xe g s T j x j g s

0 (980)

( ) :1 (0 )G PC

a

I J

New channels:

0

( )

a e e

e e


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0a Polarization

0

2 3 22 *

0, 3 * 4 2

( )( ) 2 (2 )

2 ( ) 4( )a

nn

qk k q

g g q d k qq q q m

m E k q k q

•Axis: q=(q0,0,0,qz)

•Current conservation:

•One indep. Component

•Static limit

•Recall:

1 2 0

0q

0

00

lim 0q

0, 0( 0) ( ,0)L Tq q


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A New Resonant Structure

0a NN e e

The coupling to the a0 generates a peak that is completely absent in the vacuum dilepton spectrum: a genuine in-medium signature


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Is This Observable?At the GSI, HADES has the required resolution, and the energy is appropriate to maximize the effect

Teodorescu, Dutt-Mazumder, Gale (2002)


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Squeezing dileptons out of broken symmetries, part II

• Furry’s theorem at finite T:

0

1 2 2 1

n

n

En A A A n e

1 2 2 1

n

n

En A A A n e

Sum over all states contains:1 2 2 1

n

n

En A A A n e

Furry


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Squeezing dileptons out of broken symmetries, part II

• Furry’s theorem at finite T and charge density:

1 2 2 1 1 2 2 1

( ) ( )n n n n

n n

E Q E Qn A A A n e n A A A n e

• The mirror term this time is

1 2 2 1

( )n n

n

E Qn A A A n e

Furry


McGill

So What?• Then: gg e e

32

3

2 2 2

1Tr[ ] Tr[ ]

(2 )

( ) ( )

( ) ( )

a b

n

d qT eg t t

q p k q q p

q p k q q p

Electromagnetic signature of early gluon densities!Majumder, Bourque, Gale PRC (2004), and

In progress


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Quenching = Jet-Plasma interaction

qg q

The plasma mediates a jet-photon conversion

Fries, Mueller & Srivastava, PRL 90, 132301 (2003)


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Jet-plasma interactions: EM signatures

• Real photons from quark-antiquark annihilation

• Small t and u dominate the phase space, leading to

2

2

8

9s qed u t

dt s t u

andq qp p p p

3 33

1( ) ( ) ( )

2 q q

dE s p p p p

d p

The process can be visualized as q (q)


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Photons from QCD Compton2

23s qed u s

dt s s u

33

( ) ( )q

dE s p p

d p

Photon yield from the jet-plasma interaction:( )

4 3 61

23 ( )

16

2(2 )

( 4 )(

(

)[1 ( )] ( ) ( )2

)f

q

NA

q

Agq

EdNE

d xd p

s s md p

f p

f p f p s q qE E

( )

4 3 61

23 ( )

16

2(2 )

( )[1 ( )] ( ) ( )2

( )f

q

NC

q

Cg q

EdNE

d xd p

s md

f

p f p f p s q qE E

p


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Jet characteristics are calculable


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Photon sources• Hard direct photons

• EM bremsstrahlung

• Thermal photons from hot medium

• Jet-photon conversion


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Results (photons)•RHIC


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Results (photons)•LHC

Fries, Mueller & Srivastava, PRL 90, 132301 (2003)


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Energy loss in the jet-photon conversion? Jet bremsstrahlung?

Use the approach of Arnold, Moore, and Yaffe

JHEP 12, 009 (2001); JHEP 11, 057 (2001)

• Incorporates LPM

• Complete leading order in S

• Inclusive treatment of collinear enhancement, photon and gluon

emission

Can be expressed in terms of the solution to a linear integral equation


McGill

E loss/gain: some systematics

( , )qqg k p k

( ) ( , ) ( , )( ) ( )

( , )2 ( )

q qq qg qg

q qk

gqq

g

dP p d p k k d p kP p k P p

dt dk dt dk dt

d p k kP p k

dk dt

( ) ( , ) ( , )( ) ( )

( , )( ) (2 )

q gg qg gg

q gk

g gqq gg

g

dP p d p k p d p k kP p k P p k

dt dk dt dk dt

d p k dP p k p

dk dt dk dt

•Includes E gain•Evolves the whole distribution function


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Time-evolution of quark distribution

Time-evolution of an initially monoenergetic ensemble of quarks. Evolution of only the avg. Eis also shownS.Jeon and G. Moore, hep-ph/0309332

The entiredistribution isevolved by the collision Kernel(s)

Turbide, Gale, Jeon, and Moore (2004)


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Energy loss: hadrons

• Energy loss systematics not in conflict with experimental data

Turbide, Gale, Jeon, and Moore (2004)


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Jet-bremss.:

RHIC jet-plasma photons

With E loss


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E loss: photons


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McGillFries, Srivastava, Gale (2004)


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Jet-plasma interactions: measurable EM signatures!

• RHIC:– Jet-plasma interaction is the dominant source of

photons up to pT ~ 6 GeV. – Conclusions unchanged by energy-loss considerations– Dilepton signal competes with Drell-Yan (NLO)

• LHC:– Jet-plasma photon signal is still important– Large mass lepton pairs dominate over Drell-Yan

emission.

Towards a consistent treatment of jets & EM radiation


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Summary & Conclusion• Low and intermediate mass dileptons: theory is in

good shape: NA60• Soft real photons: a (first) window to chiral symmetry?• There are measurable electromagnetic signatures of

jet-plasma interaction: those constitute complementary observables that would signal the existence of conditions suitable for jet-quenching to take place.

• EM radiation and hard probes: the start of a beautiful friendship…


McGill

International workshop on electromagnetic probes of relativistic nuclear collisions

June 2-12, 2005P. Braun-Munzinger, C. Gale, R. Rapp (coordinator)

ECT*EUROPEAN CENTRE FOR THEORETICAL

STUDIES IN NUCLEAR PHYSICS AND RELATED AREASTRENTO, ITALY

Documents

Charles Gale McGill Hard Probes 2004 In-medium effects on electromagnetic probes Hard Probes 2004 International Conference on Hard and Electromagnetic