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J. RuppertQuark Matter 2006, Nov. 2006 What does the rho do? NA60’s dimuon experiment and in-medium modifications of vector mesons Jörg Ruppert Nuclear.

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Presentation on theme: "J. RuppertQuark Matter 2006, Nov. 2006 What does the rho do? NA60’s dimuon experiment and in-medium modifications of vector mesons Jörg Ruppert Nuclear."— Presentation transcript:

1 J. RuppertQuark Matter 2006, Nov. 2006 What does the rho do? NA60’s dimuon experiment and in-medium modifications of vector mesons Jörg Ruppert Nuclear Theory, Department of Physics, McGill University, Montreal, Quebec, Canada In collaboration with: Thorsten Renk Department of Physics, University of Jyväskylä, Jyväskylä, Finland

2 J. RuppertQuark Matter 2006, Nov. 2006 Outline 1.Dilepton emission in URHIC 2.Dynamical Evolution 3.In-Medium modifications 4.NA60’s 158 AGeV In-In di-muon spectra 5.Conclusions

3 J. RuppertQuark Matter 2006, Nov. 2006 Focus on dileptons in low mass region in this talk EM probes in URHIC

4 J. RuppertQuark Matter 2006, Nov. 2006 What to learn from dilepton emission? Averaged in-medium photon spectral function (EM correlator) In-medium EM current-current correlator and dynamical evolution of the system are folded in order to predict the spectrum. On top of that contributions from non-thermal sources (hadron decays, Drell-Yan, open charm etc.) (modulus factor accounting for finite lepton masses) (Equilibrium description, for first non-equilibrium studies see Schenke, Greiner)

5 J. RuppertQuark Matter 2006, Nov. 2006 Evolution vs. EM correlator

6 J. RuppertQuark Matter 2006, Nov. 2006 Reliable (extensively tested for PbPb) fireball evolution model as basis for In-In calculations! T. Renk (2005) Dynamical evolution model for URHIC

7 J. RuppertQuark Matter 2006, Nov. 2006 “Vacuum rho” vs. “cocktail rho” Concept introduced and importance of vacuum rho contribution pointed out in Renk, Ruppert, hep-ph/0605130. Contribution is important for all centrality classes!

8 J. RuppertQuark Matter 2006, Nov. 2006 Flow profile and p t

9 J. RuppertQuark Matter 2006, Nov. 2006 Vector-meson dominance The current-field identity (J. J. Sakurai) Spectral density Dilepton emission in URHIC in the low mass region can teach us about in-medium modifications of vector mesons spectral densities once the dynamical evolution is fixed!

10 J. RuppertQuark Matter 2006, Nov. 2006 In-Medium vector mesons Vector-meson spectral densities as calculated in hadronic many-body approaches. E.g. Rapp & Wambach (1999), Lichard & Gale (1994), Renk&Mishra (2004), Lichard & Juran (2006) Vector-meson spectral densities as inferred from experiment. E.g. Shuryak (1991); Eletsky & Ioffe (1997); Eletsky, Belkacem, Ellis, Kapusta (2001); Martell & Ellis (2004), Klingl, Kaiser, Weise (1997)

11 J. RuppertQuark Matter 2006, Nov. 2006 Hot meson gas in Phi-functional approach Nota Bene: Results for in-medium modifications of the rho-meson based on Ruppert, Renk, Phys.Rev.C71:064903,2005 are to be reinvestigated (Calculations for an erratum are in progress. Prepints using this spectral function for dilepton studies will be updated.) Thanks to Knoll, Riek, and van Hees for pointing out a wrong numerical factor in the self-energy formulas and discussions regarding the influence of spurious modes on the results. Phi-Functional approach [Baym, Luttinger, Ward, Cornwall, Jackiw, Tomboulis] All results presented here don’t rely on this approach.

12 J. RuppertQuark Matter 2006, Nov. 2006 Vector Meson spectral densities as inferred from experiment Eletsky, Belkacem, Ellis, Kapusta (2001) Contribution to retarded self-energy from rho/ particle pion/nucleon scattering Scattering amplitude in cm-frame from rho/ particle pion/nucleon scattering Shuryak (1991), Eletsky & Ioffe (1997)

13 J. RuppertQuark Matter 2006, Nov. 2006 Comparison to NA60 data QGP quasi-particle picture, (Schneider et al. (2002)) In-medium Rho spectral function (Eletsky et. al. (2001)) In-medium Omega spectral function (Martell & Ellis (2004)) (Results were obtained by folding with the schematic acceptance matrix, not the full MC acceptance simulation.) In-medium Phi not (yet) included Renk, Ruppert (2006) Contributions included in our calculation:

14 J. RuppertQuark Matter 2006, Nov. 2006 P t -cut M-spectra (Results were obtained by folding with the schematic acceptance matrix, not the full MC acceptance simulation. Theory curves for high p_T are integrated up to p_T<1.5 GeV.) Renk, Ruppert (2006)

15 J. RuppertQuark Matter 2006, Nov. 2006 Results for central collisions (Results were obtained by folding with the schematic acceptance matrix, not the full MC acceptance simulation.) Renk, Ruppert (2006)

16 J. RuppertQuark Matter 2006, Nov. 2006 p t - spectra Good description in low-mass, rho-like, and higher-mass region can already be obtained with the original version of the scaled evolution (hep-ph/0605130). Adjustment in flow profile lead only to a ~10 MeV change in slope. Model accounts for the data above p_T>0.5 GeV.

17 J. RuppertQuark Matter 2006, Nov. 2006 What to learn from p t - spectra? Rather insensitive to intrinsic momentum dependences of in-medium hadronic spectral-functions and QGP rate, sensitive to emission temperature and flow => Tool to characterize emission region. p T -spectrum above ~1 GeV (in 0.6 1.0 GeV region. Effective T* is significantly lower in 1.0<M<1.4 GeV integrated region. This is an strong indication of a different source in comparison to lower mass regions. p T -spectrum in 1.0<M<1.4 GeV integrated region is in our evolution dominated by a partonic source.

18 J. RuppertQuark Matter 2006, Nov. 2006 Compilation by S. Damjanovic p t -spectra model-comparison

19 J. RuppertQuark Matter 2006, Nov. 2006 What about 4pi contribution? Suggested as dominant source due to chiral mixing in the M>1 GeV region by van Hees & Rapp (2006) (for details of their approach see next talk). We employed a different rate to study 4-pi contributions in our evolution, namely 4-pion annihilation rates by Lichard (2006) (cmp. also Lichard & Juran (2006)). Assumption: 4pi-processes are contributing as 2pi-processes all the way down to T f =130 MeV (augmented by the corresponding fugacity factor). Gives an upper limit of the contribution. Lichard (2006), hadronic interaction adjusted to describe BaBar Data In-medium-Phi not (yet) included. Renk, Ruppert (2006)

20 J. RuppertQuark Matter 2006, Nov. 2006 Discrimination of dominant source in M>1.0 GeV region via p t - spectra Different mechanisms: Experimentum crucis QGP dominant, contributes at higher T, low flow. If this is the dominant source=> lower effective T* in dilepton p t - spectra (1.0<M<1.4 GeV integrated) 4pi-annihilation, contributes significantly close to T f << T c (augmented by fugacity factor), considerable flow has built up. If dominant source => higher effective T* in p t - spectra (1.0<M<1.4 GeV integrated) General argument based on flow is not specific to one evolution model!

21 J. RuppertQuark Matter 2006, Nov. 2006 Summary Reliable dynamical evolution essential to infer information about in-medium modifications of EM-current-current correlator Different sources (Vacuum rho, in-medium vector mesons, QGP, 4pi) built up dilepton-spectrum! Still clear message from low mass dileptons => Substantial in-medium broadening of the Rho-meson necessary to describe low mass dimuon enhancement. Substantial broadening of Rho-meson caused by scattering off from nucleons and pions (Eletsky et al. (2002)), partial contribution from pion scattering in In-In substantial. In-medium broadening including scattering off by nucleons and pions seem to be on the same order as Rapp/Wambach (1999) approach. (see talks R. Rapp and H. van Hees). p t - spectra can probe different stages of the medium-evolution and reveal information about the dominant sources in different mass regions. Important: flow must be implemented consistently. Experimental p t - spectra indicates substantial contribution from partonic component in the 1 GeV<M<1.5 GeV region. Outlook: Calculations for the IMR region 1 Gev<M<3 GeV. Special thanks to S. Damjanovic, C. Gale, J. Kapusta, P. Lichard, B. Müller, B. Neufeld, H. Specht

22 J. RuppertQuark Matter 2006, Nov. 2006

23 J. RuppertQuark Matter 2006, Nov. 2006 4-pion annihilation as inferred from hadronic interactions Lichard (2006) Example: Annihilation of four charged pions into a rho-meson and via VMD into dileptons. Comparison between model prediction an inverse process Measurement by BaBaR.

24 J. RuppertQuark Matter 2006, Nov. 2006


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