Two scales of the hadronic structure

1. Two scales of the hadronic structure Search for clean signatures in the data Bogdan Povh

2. Gluonic mini-clouds of the valence quarks • Introduction • Diffractive cross section is surprisingly small • Hadronic cross sections rise slowly • Diffractive cone hardly shrinks with energy • Gluon shadowing is weak • Conclusion "anschaulich"

3. Introduction The first evidences for the smallness of the gluonic clouds come from the ISR-experiments but they have been formally interpreted within the Regge-phenomenology with no connection to hadronic structure (small triple pomeron coupling)

4. Introduction I will reinterpret the data in a less formal way, showing that the weakness of diffraction is related to smallness of gluonic clouds. I will argue that the radius of the gluonic spots suggested by data is about 0.3 fm. This is small as compared to to the confinement radius of 1 fm (in fact one has to compare these numbers squared)

5. Introduction Theoretically small r0=0.3 fm is not a surprise. • Lattice-calculation • Instanton-liquid model • Quark model with gluons of mg=0.8 GeV

6. Introduction Any high energy reaction via the strong interaction carries the information on the size of the gluon cloud. But, in general, cannot be unambiguously interpreted. Diffraction seems to be the unique way to probe directly the gluonic structure of hadrons.

7. Diffraction At high energies and large Mx diffraction is dominated by gluon bremsstrahlung. Mx Colorless exchange

8. Diffraction At low energies the neutral object is qq exchange (Regge exchange) but the cross section drops with energy ~ s-1/2 and Mx dependence The gluon bremsstrahlung gives different Mx dependence because the gluon is a vector particle

9. Diffraction The 1/M2 mass distribution at fixed s and t is the signature of gluon bremsstrahlung. Analogy to photon bremsstrahlung in spite of the difference of photon and gluon.

10. Diffraction ...

11. Diffraction Inclusive cross section for the reaction pp->pX at ISR

12. Diffraction ln (s/Mx2) = rapidity gap P: Pomeron scaling gluon bremsstrahlung gPpp (gPpp)2~ stot gPpp gPpp

13. Diffraction naïve expectation: The Pomeron-proton total cross section

14. Diffraction The gluon cloud of the valence quark is small. r02 = 0.1 fm2 Neither the single gluon comes far from the quark nor two gluons can couple to the color singlet if they are more than 0.3 fm apart.

15. Diffraction in DIS Similar results are obtained in diffraction in DIS from the H1 and ZEUS data by Hauptmann und Soper. gx q q r0 = 0.2 fm p p

16. Proton-proton cross section Schematic total cross sections of pions, kaons, protons/antiprotons and photons on the proton

17. R R0 Proton-proton cross section The transverse distances between the quarks s independent The s dependence comes from the gluon bremsstrahlung Random walk

18. Proton-proton cross section Our model: Kopeliovich, Potashnikova, bp and Predazzi Our prediction: Experiment:

19. Proton-proton cross section Differential cross sections of elastic pp and pp scattering. Imaginary part of partial amplitude as a function of the impact parameter.

20. Proton-proton cross section pp (solid circles) and pp (open circles) cross sections at s1/2 > 10 GeV elastic slope and our predictions

21. Photoproduction of J/y It is good to have a hadron-proton elasctic scattering far away from the unitary limit. D and a’ agree with our parameters before the unitary correction.

22. Photoproduction of J/y Differential cross sections for the exclusive photoproduction of J/y.

23. Photoproduction of J/y Values of the slope b, of the t distribution, plotted as a function of W.

26. Gluon shadowing Boost x Reduction of the gluon density by x

27. Gluon shadowing PQCD gives huge shadowing. Observed small. For shadowing one needs also transverse overlap.

28. J Conclusion "anschaulich" Chew-Frautschi plot

29. Conclusion "anschaulich" Chew-Frautschi plot The Regge trajectory simulates the collective effect of exchanging all members of a family of particles. When t is negative it is the square of the momentum transferred in the exchange. Positive t is the squared mass of the physical particles of spin 1, 3, 5,...

30. Conclusion "anschaulich" For linear potential (string) gives m2 ~ J slope naive expectation for a'P = 4/9 0.9 GeV-2 = 0.4 GeV-2 measured a'P = 0.1 GeV-2 kP = 8 GeV/fm

31. Backup Slides

33. Color glass codensate = gluon shadowing as function of k^ One would expect: 1 k^ 0

34. -kT h 1-x Mx x kT Diffraction

35. Photoproduction of J/y Measurements of d, b0, a’ and a(0) obtained separately from the electron and muon decay channels.