Charles GaleMcGill

Intermediate-mass lepton pairsIntermediate-mass lepton pairsin relativistic heavy-ion collisionsin relativistic heavy-ion collisions

Charles GaleCharles GaleMcGillMcGill

Charles GaleMcGill

• The physics of (very) hot and dense matter is best explored in the laboratory with relativistic nuclear collisions

• Photons and dileptons are penetrating probes

Introduction and Outline

0.2

0.007s

em

• New physics: collective, many-body effects• Quark-gluon plasma• In-medium modifications

– Modified spectral densities– Chiral symmetry restoration– Mixing effects– Pion dispersion relation

Charles GaleMcGill

Outline, cont’nd

• Experiments (IM): DLS, Helios, NA-38, -50, -60 CERES,WA98, HADES, PHENIX

• Electromagnetic radiation as a tool for hadronic tomography:– Low mass dileptons– Intermediate mass dileptons– Low pT photons– High pT photons– High pT intermediate mass

dileptons

SPS

RHICLHC

Sangyong Jeon’s talk

Charles GaleMcGill

Why? Investigation of the QCD phase diagram

S. B. Ruster et al., PRD 72, 034004 (2005)

F. Karsch, E. Laermann, hep-lat/0305025

Charles GaleMcGill

How? The information carried by EM probes

3

3 3

1Im ( )

(2 ) 1Rd R g

kd k e

Emission rates:

[photons]

6 2

3 3 6 4

2 1 1Im ( )

(2 ) 1Rd R e

E E L kd p d p k e

[dileptons]

•The electromagnetic spectra will be direct probes of the in-medium photon self-energy•They are hard probes:

•EM signals as probes for hadronic tomography

EM 3%s

McLerran, Toimela (85), Weldon (90), Gale, Kapusta (91)

Charles GaleMcGill

The current-current correlatorA 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. Rates need to be integrated

over the space-time history, with some dynamical model

3 3( , ) Im ( , )RdR

E E C p p k Td p d p

D

2 2 2 2 2 2( , )

L TP P k kk T

k m F k m G m k

D

Charles GaleMcGill

What is expected (dileptons)• Low masses receive

significant contribution from radiative decays

• High masses dominated by DY

• Intermediate mass region interesting from QGP perspective, (Shuryak (78), Shor (89))

• Photons: similar story, but featureless spectra

• Experiments: DLS, Helios, TAPS, NA38, -50, WA98, CERES, PHENIX, HADES, NA60

DD

Charles GaleMcGill

Vector Meson Spectral Densities: A Sample Calculation I

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

Charles GaleMcGill

The interaction is constrained by basic hadronic phenomenology

Chiral, Massive Yang-Mills:O. Kaymakcalan, S. Rajeev, J. Schechter, PRD 30, 594 (1984)

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

Charles GaleMcGill

Low Masses:Vector Meson Spectral Densities:Hot Meson Gas

The spectral density is flattened

and broadened. Even more with

baryons.

Rapp, Gale (PRC, 99)

Charles GaleMcGill

NA60 Comparison of data to RW, BR and NA60 Comparison of data to RW, BR and Vacuum Vacuum

pT dependence

Sanja DamjanovicQuark Matter 05 (andthis meeting)

New!

New!

Charles GaleMcGill

Two approaches:H. Van Hess, R. Rapp, nucl-th/0603084

T. Renk, J. Ruppert, hep-ph/0603110See J. Ruppert’s talk this aft.

Many-body (in-medium) effects are observed!

Charles GaleMcGill

The intermediate mass sector: some background

• Direct connection to Hard Probes

• Off-shell effects are potentially important for effective hadronic interactions Gao & Gale, PRC 57, 254 (1998)

DD_

DY

NA50Pb-Pb 158 GeV

central collisions

charm DY

A. Shor, PLB 233, 231 (1989)

Charles GaleMcGill

On the dangers of extrapolations…• (a) B. A. Li, Phys.

Rev D 52, 5165 (1995).

• (b) Gomm, Kaymakcalan, Schechter, Phys. Rev. D 30, 2345 (1984).

• (c) Janssen, Holinde, Speth, Phys. Rev. C 49, 2763 (1994).

• (d) Ko, Rudaz, Phys. Rev. D 50, 6867 (1994).

• (e) Xiong, Shuryak, Brown, Phys. Rev. D 46, 3798 (1992).

Gao & Gale, PRC 57, 254 (1998)

But, a lot of data exists!...

Charles GaleMcGill

e+ e- Data: A Wealth of Information

• OLYA

• CMD

• DM-1(2)

• ARGUS

• M3N

•

Charles GaleMcGill

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)

Charles GaleMcGill

A larger comparison

• Agreement across theoretical

models

• Those channels are mostly absent from the spectral densities used in comparisons with CERES and the new NA60 data.

Charles GaleMcGill

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)

Charles GaleMcGill

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)

Charles GaleMcGill

NA60 IMR analysis: weighted offset fits (A. David’s talk)

or

Fix Charm contribution to “world average” value

Fix Charm contribution to NA50 p-A expected value

Fit always requires ~2 times more Prompts

1

Extract prompts by fixing Open Charm contribution

Charles GaleMcGill

Low and Intermediate masses: partial summary

• Thermal sources shine in the LMR and IMR. No great sensitivity to the QGP. Intermediate-mass excess is not charm enhancement!

• The new data is precise enough to consider a differentiation of space-time models

• DY? At low M, medium-enhanced multiple parton scatterings might be large (Qiu, Zhang (02), Fries, Schaefer, Stein, Mueller (00). pA measurement.)

2 21 ( )NNAB

AB

ddAB R Q

dQ dQ

Charles GaleMcGill

A recent analysis: (van Hees & Rapp, hep-ph/0603084)

•Sensitive to the space-time modeling:•Still sensitive to the low-mass spectral densities

(4 )R e

Analyses should be redone with those

Charles GaleMcGill

Homework

• Unite (standardize?) space-time modeling [nD hydro, fireballs, transport approaches…].

• The power of the data is fully realized if a general-purpose acceptance filter exists. (On the way!...)

• Chiral symmetry? Still not obvious… An independent access to a1 spectral density is missing. More work on the theory side too. (Urban, Buballa, Hochsch. & Wambach, PRL, 88, 042002 (2002))

Charles GaleMcGill

Charles GaleMcGill

hadrons

q

q

hadrons

leadingparticle

leading particle

Jet-quenching

hadrons

q

q

hadrons

leadingparticle suppressed

leading particle suppressed

Source of energy loss: medium-induced gluonBremsstrahlung (+ elastic scattering?)

Charles GaleMcGill

Quenching = Jet-Plasma interaction. Does this have an EM signature?

qg q

The plasma mediates a jet-photon conversion

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

Charles GaleMcGill

Photon sources• Hard direct photons

• Fragmentation

• Thermal photons from hot medium

• Jet-photon conversion

• Jet in-medium bremsstrahlung

Charles GaleMcGill

Dilepton sources• Drell-Yan dileptons

• Thermal dileptons

• Jet-virtual photon conversion

Charles GaleMcGill

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

Charles GaleMcGill

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

S. Jeon’s talk

Charles GaleMcGill

Jet characteristics:

Charles GaleMcGill

Time-evolution of quark distribution

The entiredistribution isevolved by the collision Kernel(s)of the FP equation

Turbide, Gale, Jeon, and Moore (2004)

Charles GaleMcGill

Jet-plasma dileptons?• Same basic idea as photons, details are slightly

different:– High pT cut helps with background subtraction

• Go beyond LO, do a HTL analysis4

4 4 2

Im

12 1

R

E

d R

d p M e

2 32

3( ) 3 Tr ( ) ( )

(2 )f

Df n

e d qp e T S q S q p

e

0 0

( )2 ( ) 2 ( )D

q qS q

D q D q

0( )D q iq q A B

Charles GaleMcGill

The thermal “baseline” calculation agrees with that of M. Thoma, C. T. Traxler, Phys. Rev. D 56, 198 (1997)

Im

Charles GaleMcGill

Dileptons from jet-thermal interactions•Jet-thermal as large as DY/heavy quark decay (RHIC)•Jet-thermal still as large as DY. S/B could improve with harder pT cut.•At RHIC, there is a contribution to the IM region•In-medium jet bremsstrahlung will also add to the signal•No heavy quark energy loss•Signal as large as it is for photons

Turbide, Gale, Srivastava, Fries, PRC (2006)

Charles GaleMcGill

But: other signature of jet-photon conversion?

• Jet-plasma photons will come out of the

hadron-blind region. “Optical” v2 < 0

1 2 cos2 n

nT T T T

dN dNv n

p dp d p dp

Turbide, Gale, Fries (PRL 06)

Charles GaleMcGill

Photons from primordial interactions and fragmenting jetsAll photons (NN, frag, jet-photon conv., bremss., Th.)

0 + - - +

Charles GaleMcGill

• v2 from “Isolated photon cut” is negative• Photons associated with a “crowded photon cut” show v2 with changing sign• Same game can be played with dileptons (in progress)• See talk by U. Heinz

Similar story for the LHC

Charles GaleMcGill

Jet-plasma interactions: measurable EM signatures! These are fairly robust with respect to changing temperature & dynamics

• RHIC & LHC:– Jet-plasma interactions: dilepton channel: signal

competes with Drell-Yan (NLO)

Towards a consistent treatment of jets & EM radiation

Intermediate-mass dileptons•New data will put further stringent tests on models, both rates & space-time modeling

Conclusions, part I

Charles GaleMcGill

Conclusions, part II

• Low and mass dileptons: NA60 data can distinguish between models. In-medium effects!

• RHIC/LHC: There are measurable electromagnetic signatures of jet-plasma interaction: those constitute complementary observables to signal the existence of conditions suitable for jet-quenching

• Photon v2: a revealing probe • EM radiation and hard probes: the start of a

beautiful friendship…• EM radiation: change of paradigm

Charles GaleMcGill

• Interested in the techniques discussed here?

• Want to know more?

Found where fine books are sold(July 2006)

Charles GaleMcGill

Charles GaleMcGill

• Chatterjee, Frodermann, Heinz, Srivastava, nucl-th/0511079

Charles GaleMcGill

Jet-plasma photons:

• S. Jeon’s talk

Charles GaleMcGill

New (preliminary) PHENIX Data

Charles GaleMcGill

Charles GaleMcGill

Vector Meson Spectral Densities, II(adding baryons)

R. Rapp & J.Wambach, 1999

Charles GaleMcGill

Soft photons @ RHIC:

• There is a window

Turbide, Rapp & Gale PRC (2004)

Charles GaleMcGill

Same spectral densities:Low mass dileptons and real photons

S. Turbide, R. Rapp, and C. Gale, PRC (2004)

Charles GaleMcGill

• 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