Parton-Hadron Transition in Nuclear Physics

1. Parton-Hadron Transition in Nuclear Physics Haiyan Gao1,2 1. Duke University 2. Massachusetts Institute of Technology Nuclear Particle Physics Colloquium MIT March 10, 2003

2. Two “Realms” of Nuclear Physics

3. Static potential between (lattice)

4. Nucleon-meson degrees of freedom effective at low energies • Quark-gluon degrees of freedom at high energies • Where is the transition?

5. Parton-Hadron Transition in Nuclear Physics Simplest systems: pion, nucleon, deuteron • Form factors • Deuteron photodisintegration • Photopion production from nucleon Photopion production from nuclei

6. Signatures for the transition? • Constituent quark counting rule (Brodsky-Farrar) • Dimensional analysis • pQCD analysis • Support by experiments • Hadron helicity conservation • Quark orbital angular momentum? • What else (nuclei as laboratories)? • Nuclear filtering • Color transparency • Others….

7. Constituent Quark Counting • Based on dimensional analysis, confirmed by short-distance pQCD analysis • Power law predictions for form factors:pion, nucleon, deuteron …… • Two-body exclusive process A+B -> C+D

8. Charged Pion Elastic Form Factor • Simplest valence quark structure • pQCD is expected to manifest at relatively low momentum transfer • Reputable pQCD and non-pQCD calculations exist • The asymptotic pion form factor

10. Ratio for the Reaction Huang and Kroll, Euro. Phys. J. C17 (2000)

11. Charged Pion Ratio from Photoproduction 900 c.m.

12. 900 c.m.

13. Nucleon Electromagnetic Form Factor Spin-1/2 object F1 (Dirac), 1/Q4 F2 (Pauli), 1/Q6 GE, GM: linear Combination of F1 and F2

15. pQCD Analysis Belitsky, Ji and Yuan carried out pQCD analysis (hep-0212351):

16. pQCD?

17. How far can one go? 11 GeV Proj.

18. Deuteron Structure Spin-1 nucleus, three form factors: GC, GQ, GM Quark-gluon description

19. Deuteron Form Factor

20. Constituent quark counting predicts for proton-proton elastic scattering

21. Deuteron Photodisintegration

22. Simplest nuclear reaction Data seem to show scaling at 70 and 90 degree, onset of scaling at higher energies is suggested at 36 and 52 degree

23. With MAD, deuteron Photodisintegration cross-section can be extended to 7 GeV at forward angles (less than one month)

24. Hadron Helicity Conservation??? Orbital angular momentum Recent data on proton form factor ratio from polarization transfer measurements

25. Virtual photon asymmetry: Data in disagreement with pQCD HHC based parameterization Zheng et al, to be submitted to PRL

27. Polarization measurements in deuteron photodisintegration

28. Oscillatory Scaling (QCD oscillation) Proton-proton elastic scattering

29. Interference picture • Left: Born diagram (short-distance) • Right: independent scattering amplitude (Landshoff) • Interference between the two gives rise to oscillation, spin correlation anomaly, nuclear transparency bump

30. 27Al(p,2p)

31. Origin of the oscillation? • Interference between short-distance and long-distance amplitudes • New resonance states associated with crossing a new quark flavor threshold • Intriguing momentum transfer dependence in nuclear transparency T from A(p,2p) suggests nuclear filtering effect? (suppression of long-distance amplitude in nuclear medium)

32. Generalized counting rule Ji, Ma, Yuan (hep-ph/0301141) derived the following generalized counting rule involving parton orbital angular momentum: When and minimal n, reduces to the counting Rule of Brodsky-Farrar, and Matveev- Muradian-Tavkhelidze

33. Why photopion production from nucleon? • Pion has the simplest valence quark structure • Photopion production cross-section decreases relatively slower with the increase of energy Advantageous for the study of QCD oscillation and the test of the generalized counting rule prediction by Ji, Ma and Yuan

34. Jlab Experiment E94-104 • Three unique measurements: • Coincidence measurement from deuterium target to investigate quark counting rule, from hydrogen • Singles ratio over a large t range to test various predictions • Coincidence measurement from 4He to form nuclear transparency

36. E94-104 Experiment Layout

37. Fermi Momentum Red: data Black:simulation

38. Reconstructed Photon Energy Spectrum

39. E94-104 Results

41. Hints of oscillation? • E94-104 data show global scaling behavior • Hints of oscillatory scaling?

42. JLab 12 GeV Projection HRS (100 hrs)

43. HMS+SHMS (600 hrs)

44. JLab 12 GeV Projection HRS+calorimeter (360 hrs)

45. Color transparency A novel QCD effect based on: • Point like configuration (PLC) state is produced in exclusive process at large momentum transfer • PLC state experience reduced interactions inside the nuclear medium • PLC state remains small while it propagates out of the nucleus

46. BNL A(p,2p) Experiments 27Al(p,2p)

47. JLab & SLAC results A(e,e’p)

48. FNAL A(π, dijet) Data 1.8 1.2 • Coherent π+ diffractive dissociation at 500 GeV/c • using 12C and 195Pt nuclei (Q2>4kt2) • from inclusive pion-nucleus scattering (GeV/c)

49. Incoherent r Meson Production 0 14 o HERMES (e,e’ r ) with E = 27 GeV, A = N e 2 T as a function of Q for fixed l has a slope consistent with CT. C 2.5sdeviation from traditional calculations A. Airapetian et al. , PRL 90, 052501 (2003) 2 2 Q ( GeV/c)

50. Nuclear Filtering (NF) • NF refers to the suppression of large-distance quark separation in nuclear medium • NF predicts oscillation in nuclear transparency 180o out-of-phase with free cross-section oscillation • NF is an QCD effect complementary to CT