charles gale mcgill intermediate-mass lepton pairs in relativistic heavy-ion collisions charles gale...
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Charles GaleMcGill
Intermediate-mass lepton pairsIntermediate-mass lepton pairsin relativistic heavy-ion collisionsin relativistic heavy-ion collisions
Charles GaleCharles GaleMcGillMcGill
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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
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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
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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
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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)
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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
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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
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Charles GaleMcGill
Vector Meson Spectral Densities: A Sample Calculation I
Ralf Rapp and Charles Gale, Phys. Rev. C 60, 024003 (1999)
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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
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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)
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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!
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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!
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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)
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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!...
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Charles GaleMcGill
e+ e- Data: A Wealth of Information
• OLYA
• CMD
• DM-1(2)
• ARGUS
• M3N
•
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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)
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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.
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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)
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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)
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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
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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
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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
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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))
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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?)
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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)
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Charles GaleMcGill
Photon sources• Hard direct photons
• Fragmentation
• Thermal photons from hot medium
• Jet-photon conversion
• Jet in-medium bremsstrahlung
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Charles GaleMcGill
Dilepton sources• Drell-Yan dileptons
• Thermal dileptons
• Jet-virtual photon conversion
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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
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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
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Charles GaleMcGill
Jet characteristics:
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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)
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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
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Charles GaleMcGill
The thermal “baseline” calculation agrees with that of M. Thoma, C. T. Traxler, Phys. Rev. D 56, 198 (1997)
Im
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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)
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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)
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Charles GaleMcGill
Photons from primordial interactions and fragmenting jetsAll photons (NN, frag, jet-photon conv., bremss., Th.)
0 + - - +
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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
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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
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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
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• Interested in the techniques discussed here?
• Want to know more?
Found where fine books are sold(July 2006)
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• Chatterjee, Frodermann, Heinz, Srivastava, nucl-th/0511079
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Jet-plasma photons:
• S. Jeon’s talk
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Charles GaleMcGill
New (preliminary) PHENIX Data
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Charles GaleMcGill
Vector Meson Spectral Densities, II(adding baryons)
R. Rapp & J.Wambach, 1999
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Charles GaleMcGill
Soft photons @ RHIC:
• There is a window
Turbide, Rapp & Gale PRC (2004)
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Charles GaleMcGill
Same spectral densities:Low mass dileptons and real photons
S. Turbide, R. Rapp, and C. Gale, PRC (2004)
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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