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A Bayesian Analysis of QCD Sum Rules

A Bayesian Analysis of QCD Sum Rules. arXiv: 1005.2459 [hep-ph] (to be published in PTP). Baryons`10 Osaka University 8.12.2010 Philipp Gubler (TokyoTech) Collaborators: Makoto Oka (TokyoTech), Kenji Morita (GSI). Contents. QCD Sum Rules and the Maximum Entropy Method

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A Bayesian Analysis of QCD Sum Rules

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  1. A Bayesian Analysis of QCD Sum Rules arXiv: 1005.2459 [hep-ph] (to be published in PTP) Baryons`10 Osaka University 8.12.2010 Philipp Gubler (TokyoTech) Collaborators: Makoto Oka (TokyoTech), Kenji Morita (GSI)

  2. Contents • QCD Sum Rules and the Maximum Entropy Method • Test of the method in the case of the ρmeson channel • First results of the analysis of charmonium at finite temperature • Conclusions

  3. QCD sum rules M.A. Shifman, A.I. Vainshtein and V.I. Zakharov, Nucl. Phys. B147, 385 (1979); B147, 448 (1979). In this method the properties of the two point correlation function is fully exploited: is calculated “perturbatively”, using OPE spectral function of the operator χ After the Borel transformation:

  4. The basic problem to be solved given ? “Kernel” (but only incomplete and with error) This is an ill-posed problem. But, one may have additional information on ρ(ω), which can help to constrain the problem: - Positivity: - Asymptotic values:

  5. ρ(s) s The usual approach The spectral function is usually assumed to be describable by a “pole + continuum” form (ground state + excited states): This very crude ansatz often works surprisingly well, but… This ansatz may not always be appropriate. The dependence of the physical results on sth is often quite large.

  6. The Maximum Entropy Method → Bayes’ Theorem likelihood function prior probability (Shannon-Jaynes entropy) Corresponds to ordinary χ2-fitting. “default model” M. Jarrel and J.E. Gubernatis, Phys. Rep. 269, 133 (1996). M.Asakawa, T.Hatsuda and Y.Nakahara, Prog. Part. Nucl. Phys. 46, 459 (2001).

  7. Experiment: mρ= 0.77 GeV Fρ= 0.141 GeV A first test case: the ρmeson channel The sum rule: The position and residue of the ρ-meson are reproduced, but not its width.

  8. Application to charmonium (J/ψ) at finite temperature - Prediction of “J/ψSuppression by Quark-Gluon Plasma Formation” T. Matsui and H. Satz, Phys. Lett. B 178, 416 (1986). … - During the last 10 years, a picture has emerged from studies using lattice QCD (and MEM), where J/ψ survives above TC. (schematic) M. Asakawa and T. Hatsuda, Phys. Rev. Lett. 92 012001 (2004). S. Datta et al,Phys. Rev. D69, 094507 (2004). T. Umeda et al, Eur. Phys. J. C39S1, 9 (2005). … taken from H. Satz, Nucl.Part.Phys. 32, 25 (2006).

  9. The charmonium sum rules at T=0 We analyze two different sum rules: Moment sum rules Borel sum rules Developed and analyzed in: M.A. Shifman, A.I. Vainshtein and V.I. Zakharov, Nucl. Phys. B147, 385 (1979); B147, 448 (1979). L.J. Reinders, H.R. Rubinstein and S. Yazaki, Nucl. Phys. B 186, 109 (1981). R.A. Bertlmann, Nucl. Phys. B 204, 387 (1982).

  10. Analysis at T=0 Moment sum rules Borel sum rules (Moments n=5~14 are used) mJ/ψ=3.19 GeV mJ/ψ=3.11 GeV - The J/ψ peak is obtained close to the experimental value. - We also get a (nonsignificant) second peak. → Excited states? → MEM artifact?

  11. The charmonium sum rules at finite T The application of QCD sum rules has been developed in: T.Hatsuda, Y.Koike and S.H. Lee, Nucl. Phys. B 394, 221 (1993). depend on T A non-scalar twist-2 gluon condensates appears due to the non-existence of Lorentz invariance at finite temperature: four-velocity of the medium

  12. The T-dependence of the condensates The energy-momentum tensor is considered: After matching the trace part and the traceless part, one gets: obtained from lattice QCD These values are obtained from quenched lattice calculations: G. Boyd et al, Nucl. Phys. B 469, 419 (1996). taken from: O. Kaczmarek et al, Phys. Rev. D 70, 074505 (2004). K. Morita and S.H. Lee, arXiv:0908.2856 [hep-ph]. K. Morita and S.H. Lee, Phys. Rev. Lett. 100, 022301 (2008). K. Morita and S.H. Lee, Phys. Rev. C. 77, 064904 (2008).

  13. The charmonium spectral function at finite T Moment sum rules (Moments n=5~14 are used) preliminary melting of J/ψ! Similar results are obtained with the Borel sum rules.

  14. Conclusions • We have shown that MEM can be applied to QCD sum rules • The “pole + continuum” ansatz is not a necessity • We could observe the melting of J/ψ using finite temperature QCD sum rules and MEM • J/ψ seems to melt between T ~ 1.2 TC and T ~ 1.4 TC,, which is below the values obtained in lattice QCD

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