charles gale mcgill qm 2005 thermal photons and dileptons* why? how? theory low mass dileptons...

QM 2005 Charles Gale

McGill

Thermal Photons and Dileptons*

•Why? How? Theory•Low mass dileptons•Intermediate mass

dileptons•Photons: low and high(er)

pT photons

•EM signature of jets

((** Not an exhaustive review…) Not an exhaustive review…)

QM 2005 Charles Gale

McGill

Why? 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)

QM 2005 Charles Gale

McGill

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

QM 2005 Charles Gale

McGill

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

QM 2005 Charles Gale

McGill

Expectations, part II

•Thermal QGP plasma radiation•Many-body, in-medium, effects on spectral densities

0

( , ) ( , ) 0L LV Ad p p

Weinberg (67)Kapusta, Shuryak (94)

+ other possibilities…

QM 2005 Charles Gale

McGill

UrQMD

In-medium: what medium?

Phase-space trajectory goes through qualitatively different media

QM 2005 Charles Gale

McGill

Low Masses:Vector Meson Spectral Densities:Hot Meson Gas

The spectral density is flattened

and broadened

Rapp, Gale (99)

QM 2005 Charles Gale

McGill

Vector Meson Spectral Densities, II(adding baryons)

R. Rapp & J.Wambach, 1999

QM 2005 Charles Gale

McGill

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)

QM 2005 Charles Gale

McGill

Two approaches:

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

Rapp & WambachEletsky, Ioffe, Kapusta

(Giessen, Frankfurt, Munich)

QM 2005 Charles Gale

McGill

Fold in With a Dynamical Evolution Model

Huovinen, Belkacem, Ellis, and Kapusta (02)

What’s new?

Rapp, Brown-Rho

QM 2005 Charles Gale

McGill

e+e- mass spectrum: comparison to the models

calculation by R.Rapp using Rapp/Wambach medium modification of rho spectral function

calculation by R.Rapp using Brown-Rho scaling

B. Kämpfer, thermal emission

...added to the cocktail.

in the 0.8 < m < 0.98 GeV region:Brown-Rho curve: 2/n = 2.4the other two curves: 2/n ~ 0.3

Sergey Yurevich (CERES)

QM 2005 Charles Gale

McGill

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

pT dependence

Sanja Damjanovic

QM 2005 Charles Gale

McGill

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

•Linear scale!!!Linear scale!!!•Quality of data enables a preciseQuality of data enables a precise determination of the spectraldetermination of the spectral properties.properties.•The beginning of a new era…The beginning of a new era…

QM 2005 Charles Gale

McGill

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)

• A lot of data already exists!

DD_

DY

NA50Pb-Pb 158 GeV

central collisions

charm DY

A. Shor, PLB 233, 231 (1989)

QM 2005 Charles Gale

McGill

e+ e- Data: A Wealth of Information

• OLYA

• CMD

• DM-1(2)

• ARGUS

• M3N

•

QM 2005 Charles Gale

McGill

A larger comparison

• Agreement across theoretical

models

• Those channels are absent

from the spectral densities used in comparisons with CERES and the new NA60 data.

QM 2005 Charles Gale

McGill

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)

QM 2005 Charles Gale

McGill

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)

QM 2005 Charles Gale

McGill

NA60 IMR analysis: weighted offset fits (R. Shahoyan)

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

QM 2005 Charles Gale

McGill

Low and Intermediate masses: partial summary

• Thermal sources shine in the LMR and IMR. No great sensitivity to the QGP

• The 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

QM 2005 Charles Gale

McGill

(Theory) Homework

• Unite (standardize?) space-time modeling [nD hydro, fireballs, transport approaches…]. Rapidity dependence of photon signal: a probe of stopping (Renk, PRC (05))

• The power of the data is only fully realized if a general-purpose acceptance filter exists.

QM 2005 Charles Gale

McGill

Electromagnetic radiation from QCD

First approaches

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

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

HTLresummation

QM 2005 Charles Gale

McGill

• 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: 22

2s sth

T

m

QM 2005 Charles Gale

McGill

Singularities can be re-summed

Arnold, Moore, and Yaffe

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

• Incorporates LPM

• Complete leading order in αs

• Inclusive treatment of collinear enhancement, photon and gluon

emission

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

QM 2005 Charles Gale

McGill

How big (small) is this?

Turbide, Rapp & Gale PRC (2004)

QM 2005 Charles Gale

McGill

QM 2005 Charles Gale

McGill

Azimuthal correlation– Shows the absence of “away-side” jet.

Pedestal&flow subtracted

QM 2005 Charles Gale

McGill

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)

QM 2005 Charles Gale

McGill

Photon sources• Hard direct photons

• EM bremsstrahlung

• Thermal photons from hot medium

• Jet-photon conversion

• Jet in-medium bremsstrahlung

QM 2005 Charles Gale

McGill

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

QM 2005 Charles Gale

McGill

Time-evolution of quark distribution

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

Turbide, Gale, Jeon, and Moore (2004)

QM 2005 Charles Gale

McGill

With the new (preliminary) PHENIX data

QM 2005 Charles Gale

McGill

Photons: establishing a baseline

Aurenche et al., NPB 286, 553 (1987)Consistent with Gordon & Vogelsang

(preliminary)

QM 2005 Charles Gale

McGill

Direct in d+Au

• p+p and d+Au spectra compared to NLO pQCD

• ratio to NLO pQCD• consistent with 1• No indication for

nuclear effects

2

Poster H. Torii

Poster D. Peressounko

(S. Bathe)

QM 2005 Charles Gale

McGill

RHIC jet-plasma photons

With E loss

QM 2005 Charles Gale

McGill

RHIC Au Au data

QM 2005 Charles Gale

McGill

New (preliminary) PHENIX Data(Bathe, Buesching)

*

*direct direct

inclusive inclusive

4 3 *

2 3 2 33

d d

dM d q M d q

*

*direct

direct inclusiveinclusive

÷

÷÷

0-3

0

90-1

40

140-2

00 M

eV

200-3

00

Rdata

QM 2005 Charles Gale

McGill

New (preliminary) PHENIX Data(Bathe, Buesching)

A prediction: all source

Sizes fixed prio

r to QM

QM 2005 Charles Gale

McGill

QM05 Stefan Bathe 31

The Spectrum

Compare to thermal + pQCD• data consistent with

thermal + pQCD

Compare to thermal model

• data above thermal at high pT

• D. d’Enterria, D. Perresounko

• nucl-th/0503054

Compare to NLO pQCD

• excess above pQCD

• L.E.Gordon and W. Vogelsang

• Phys. Rev. D48, 3136 (1993)

2+1 hydroT0

ave=360 MeV(T0max=570 MeV)

0=0.15 fm/ c

QM 2005 Charles Gale

McGill

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 (05)

QM 2005 Charles Gale

McGill

If photons can be detected in coincidence with hadronsThe jet-plasma photons can be easier to isolate (Cole)

QM 2005 Charles Gale

McGill

Jet-plasma interactions: measurable EM signatures!

• RHIC:– Jet-plasma interaction is a large source of photons up to

pT ~ 6 GeV. – Conclusions include energy-loss considerations– True also in the dilepton channel: signal competes with

Drell-Yan (NLO)

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

emission.

Towards a consistent treatment of jets & EM radiation

QM 2005 Charles Gale

McGill

Summary, Conclusions, Open Issues• Low and mass dileptons: NA60 data can distinguish

between models• IMR: More homework to be done (Higher twist…)• Space-time evolution models• RHIC: 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 • RHIC dileptons: systematic errors still too large to

permit source identification (A. Toia, PHENIX)• EM radiation and hard probes: the start of a

beautiful friendship…

QM 2005 Charles Gale

McGill

Collaborators:

•Simon Turbide, McGill University

•Rainer Fries, University of Minnesota

•R. Rapp, Texas A&M

•Dinesh Srivastava, VECC, Calcutta