J. Ruppert Hot Quarks 2006, May 2006

What does the rho? Lessons from NA60's di-muon measurement.

Jörg RuppertNuclear Theory, Department of Physics,

Duke University, Durham, NC, USA

In collaboration with:

Thorsten RenkDepartment of Physics,

University of Jyväskylä, Jyväskylä, Finland

J. Ruppert Hot Quarks 2006, May 2006

Outline

1. Introduction: EM Probes of strongly interacting matter

2. Dynamical Evolution3. NA60’s 158 AGeV In-In di-muon

spectra 4. From In-In to Pb-Pb5. Conclusions

J. Ruppert Hot Quarks 2006, May 2006

EM Probes of strongly interacting matter

EM Probes of strongly interacting matter

Focus on dileptons in this talk

J. Ruppert Hot Quarks 2006, May 2006

Dilepton emission from URHICDilepton emission from URHIC

URHIC produce a hot and dense medium - but it is by all means not static!

J. Ruppert Hot Quarks 2006, May 2006

Dilepton spectra in HICsDilepton spectra in HICs

Focus on low andintermediate massregion in this talk

J. Ruppert Hot Quarks 2006, May 2006

Theory of dilepton emissionTheory of dilepton emission

(modulus factor including lepton masses)

In-medium effects and the fireball evolution as input are needed!

Averaged in-medium photon spectral function(EM correlator)

On top of that non-thermal sources (hadron decays, Drell-Yan, open charm etc.)

J. Ruppert Hot Quarks 2006, May 2006

E. M. correlator in vacuumE. M. correlator in vacuum

Continuum

V

Vector meson dominance

Rho-meson dominant!

Compilation from Rapp, Wambach,

Adv.Nucl.Phys.25:1,2000

J. Ruppert Hot Quarks 2006, May 2006

Chiral symmetry breakingChiral symmetry breaking

Chiral symmetry spontanously broken in vacuum! Chiral partners in the hadronic spectrum split. Hot and dense matter excites the vacuum:Gradual restoration of chiral symmetry => Chiral partners become degenerate!

J. Ruppert Hot Quarks 2006, May 2006

Chiral symmetry restorationChiral symmetry restoration

Barate et al, ALEPH, Eur. Phys. J. C4, 409 (1998), Compilation from Rapp, Wambach,

Adv.Nucl.Phys.25:1,2000

Vacuum

Brown, Rho, Phys. Rev.

Lett., (1991)

In-Medium rho and a1In-medium chiral mixing(leading order, M large)

Broadening e. g. from hadronic many-body calculations

Compilation from Rapp, Wambach,

Adv.Nucl.Phys.25:1,2000

Dey, Eltsky, Ioffe, Phys. Lett. B252 (1990) 620

Krippa Phys. Lett. B427 (1998) 13.

J. Ruppert Hot Quarks 2006, May 2006

SU(3) chiral model at finite densities

and temperature

SU(3) chiral model at finite densities

and temperature

J. Ruppert Hot Quarks 2006, May 2006

Hot meson gas: Pion/Rho system treated in Phi - functional

approach

Hot meson gas: Pion/Rho system treated in Phi - functional

approachPhi-Functional approach [Baym, Luttinger, Ward, Cornwall, Jackiw, Tomboulis]

Systematic resummation scheme of certain classes of diagrams:Many-Body calculation that includes non-perturbative broadening effects due toa finite width of the pion. Ruppert, Renk, Phys.Rev.C71:064903,2005

approximation Self-energies

• Included: finite broadening• Not-included: mass shifts (disregard changes in the real part of the self-energy)

J. Ruppert Hot Quarks 2006, May 2006

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Dynamical evolution model for URHIC!

Dynamical evolution model for URHIC!

Reliable dynamical evolution modelabsolutely necessary!

J. Ruppert Hot Quarks 2006, May 2006

CERES dataCERES data

Compilation of calculations for the dilepton spectrum at CERES for different models of in-medium modifications. One fireball evolution model for all spectral functions Renk,Ruppert, Phys.Rev.C71:064903,2005.

Klingl, Kaiser, Weise, Nucl.Phys.A624:527-563,1997,

Renk, Schneider, Weise, Phys.Rev. C66:014902,2002,

Renk, Mishra, Phys.Rev.C69:054905,2004

J. Ruppert Hot Quarks 2006, May 2006

Rescaling for 158 AGeV In-In collisions

Rescaling for 158 AGeV In-In collisions

Since no freeze-out analysis is available the Pb-Pb collisionmodel is rescaled!The choice of the decoupling temperature TF=130 MeV is not strongly restricted. This translates primarily into an uncertainty in the normalization of the final result.

J. Ruppert Hot Quarks 2006, May 2006

Comparison with NA60Comparison with NA60

pt>1 GeVpt<0.5 GeV

Pt integrated

J. Ruppert Hot Quarks 2006, May 2006

From In-In to Pb-Pb!From In-In to Pb-Pb!

pt<0.5 GeV

Pt integrated

pt>1 GeV

J. Ruppert Hot Quarks 2006, May 2006

What dominates M>1 GeV? QGP vs. low T

four pion annihilation?

What dominates M>1 GeV? QGP vs. low T

four pion annihilation?

van Hees, Rapp, hep-ph/0603084

Low T contributions would be significant due to fugacity !

Is such a description valid down to Tf?

Is chiral mixing effective at low T?Can low T contributions account for NA60’s pt cuts (next slide)?

?

?

J. Ruppert Hot Quarks 2006, May 2006

QGP vs. low T four pion: pt-dependence

QGP vs. low T four pion: pt-dependence

Significant QGP contribution (high T, insignificant flow)

High T => exponentialSpectrum in pt

Significant low T chiral mixing contribution (significant flow)

Flow pushes to higher pt =>exponential spectrum withshoulder in pt Different evolution models (different T, different flow) can

lead to similar spectra either at low pt or high pt at given M but not at both..

J. Ruppert Hot Quarks 2006, May 2006

Comparison I: Integrated pt Comparison I: Integrated pt

van Hees, RappRenk, Ruppert, hep-ph/0605130

J. Ruppert Hot Quarks 2006, May 2006

Comparison II: pt<0.5 GeVComparison II: pt<0.5 GeV

van Hees, RappRenk, Ruppert, hep-ph/0605130

J. Ruppert Hot Quarks 2006, May 2006

Comparison III: pt>1 GeVComparison III: pt>1 GeV

van Hees, RappRenk, Ruppert, hep-ph/0605130

J. Ruppert Hot Quarks 2006, May 2006

ConclusionsConclusions