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…)


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)


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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


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


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…


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UrQMD

In-medium: what medium?

Phase-space trajectory goes through qualitatively different media


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Low Masses:Vector Meson Spectral Densities:Hot Meson Gas

The spectral density is flattened

and broadened

Rapp, Gale (99)


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Vector Meson Spectral Densities, II(adding baryons)

R. Rapp & J.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•Lagrangians are constrained by hadronic phenomenology•Mass shifts & broadening are related by dispersion relations

Rapp & WambachEletsky, Ioffe, Kapusta

(Giessen, Frankfurt, Munich)


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Fold in With a Dynamical Evolution Model

Huovinen, Belkacem, Ellis, and Kapusta (02)

What’s new?

Rapp, Brown-Rho


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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)


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

pT dependence

Sanja Damjanovic


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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…


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)


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e+ e- Data: A Wealth of Information

• OLYA

• CMD

• DM-1(2)

• ARGUS

• M3N

•


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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.


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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)


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)


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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


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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


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.


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


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


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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 αs

• 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?

Turbide, Rapp & Gale PRC (2004)


McGill


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

Pedestal&flow subtracted


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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)


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Photon sources• Hard direct photons

• EM bremsstrahlung

• Thermal photons from hot medium

• Jet-photon conversion

• Jet in-medium bremsstrahlung


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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

Time-evolution of quark distribution

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

Turbide, Gale, Jeon, and Moore (2004)


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With the new (preliminary) PHENIX data


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Photons: establishing a baseline

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

(preliminary)


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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)


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RHIC jet-plasma photons

With E loss


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RHIC Au Au data


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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


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New (preliminary) PHENIX Data(Bathe, Buesching)

A prediction: all source

Sizes fixed prio

r to QM


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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


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)


McGill

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


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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


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…


McGill

Collaborators:

•Simon Turbide, McGill University

•Rainer Fries, University of Minnesota

•R. Rapp, Texas A&M

•Dinesh Srivastava, VECC, Calcutta

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

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