1. Primakoff Experiments with EIC Outline • Physics motivation: • The first experiment at JLab: 0 lifetime • Development of precision technique • Results for 0 lifetime • Experiments with EIC • Summary A. Gasparian NC A&T State University, Greensboro, NC For the PrimEx Collaboration 1

2. The QCD Lagrangian chiral limit:is the limit of vanishing quark masses mq→ 0. QCD Lagrangian with quark masses set to zero: Large global symmetry group:

3. Fate of QCD Symmetries

4. Lightest Pseudoscalar Mesoms • Chiral SUL(3)XSUR(3) spontaneously broken Goldstone mesons π0, η8 • Chiral anomalies Mass of η0 P→γγ ( P: π0, η, η׳) • Quark flavor SU(3) breaking The mixing of π0, η and η׳ The 0, η and η’ system provides a rich laboratory to study the symmetry structure of QCD at low energy.

5. Experimental program Precision measurements of: Two-Photon Decay Widths: Γ(0→), Γ(→), Γ(’→) Transition Form Factors at low Q2 (0.001-0.5 GeV2/c2): F(*→0), F(* →), F(* →) The PrimEx Experimental Project Test of Chiral Symmetry and Anomalies via the Primakoff Effect 5

6. Physics Outcome Fundamental input to Physics: • precision test of chiral anomaly predictions • determination of quark mass ratio • -’ mixing angle • 0, and ’ interaction electromagnetic radii • is the ’ an approximate Goldstone boson? 6

7. First experiment: 0 decay width • 0→ decay proceeds primarily via the chiral anomaly in QCD. • The chiral anomaly prediction is exact for massless quarks: • Corrections to the chiral anomaly prediction: (u-d quark masses and mass differences) Calculations in NLO ChPT: (J. Goity, at al. Phys. Rev. D66:076014, 2002) Γ(0) = 8.10eV ± 1.0% ~4% higher than LO, uncertainty: less than 1% • Recent calculations in QCD sum rule: (B.L. Ioffe, et al. Phys. Lett. B647, p. 389, 2007) • Γ() is only input parameter • 0- mixing included Γ(0) = 7.93eV ± 1.5% 0→ • Precision measurements of (0→) at the percent levelwill provide a stringent test of a fundamental prediction of QCD.

8. Decay Length Measurements (Direct Method) Measure 0decay length 1x10-16 sec too small to measure solution: Create energetic 0 ‘s, L = vE/m But, for E= 1000 GeV, Lmean 100 μm very challenging experiment 1984 CERN experiment: P=450 GeV proton beam Two variable separation (5-250m) foils Result: (0) = 7.34eV3.1% (total) • Major limitations of method • unknown P0 spectrum • needs higher energies for improvement 0→

9. e+e- Collider Experiment DORIS II @ DESY e+e-e+e-**e+e-0e+e- e+,e- scattered at small angles (not detected) only  detected Results: Γ(0) = 7.7 ± 0.5 ± 0.5 eV ( ± 10.0%) 0→ • Not included in PDG average • Major limitations of method • knowledge of luminosity • unknown q2 for **

10. ρ,ω Primakoff Method 12C target Primakoff Nucl. Coherent Nucl. Incoh. Interference Challenge: Extract the Primakoff amplitude from the experimental cross section 10

11. Previous Primakoff Experiments • DESY (1970) • bremsstrahlung  beam, E=1.5 and 2.5 GeV • Targets C, Zn, Al, Pb • Result: (0)=(11.71.2) eV 10.% • Cornell (1974) • bremsstrahlung  beam E=4 and 6 GeV • targets: Be, Al, Cu, Ag, U • Result: (0)=(7.920.42) eV 5.3% • All previous experiments used: • Untagged bremsstrahlung  beam • Conventional Pb-glass calorimetry

12. PrimEx Experiment at Hall B JLab • Requirements of Setup: • high angular resolution (~0.5 mrad) • high resolutions in calorimeter • small beam spot size (‹1mm) • Background: • tagging system needed • Particle ID for (-charged part.) • veto detectors needed • JLab Hall B high resolution, high intensity photon tagging facility • New pair spectrometer for photon flux control at high intensities • New high resolution hybrid multi-channel calorimeter (HYCAL)

13. Fit to Extract Γ(0) Decay Width • Theoretical angular distributions smeared with experimental resolutions are fit to the data 12C 208Pb 13

14. Estimated Systematic Errors L. Gan APS, April 15, 2008 14

15. Current PrimEx Result () = 7.93eV2.3%1.6% 15

16. Next Run 1.4% 16

17. PrimEx @ High Energies with EIC Experimental program Precision measurements of: Transition Form Factors at low Q2 (0.001-0.5 GeV2/c2): F(*→0), F(* →), F(* →) 17

18. ρ,ω Primakoff Method 12C target Primakoff Nucl. Coherent Interference Nucl. Incoh. Challenge: Extract the Primakoff amplitude 18

19. Why do we need high energy? • Increase Primakoff cross section: • Better separation of Primakoff reaction from nuclear processes: • Momentum transfer to the nuclei becomes less reduce the incoherent background

20. Transition Form Factors at Law Q2 • Direct measurements of slopes: F(*→0), F(* →), F(* →) • Interaction radii: Fγγ*P(Q2) ≈ 1 - 1/6▪<r2>PQ2 • ChPT for large Nc predicts relation between the slopes. • Extraction of Ο(p6) low-energy constant in the chiral Lagrangian • Extraction of decay widths: Γ(0→), Γ(→), Γ(’→) • Precision test of chiral anomaly predictions

21. Experimental Status for F(*→0) F(*→0) ≈ 1 – a Q2/m2

22. Experimental Status for F(* →)

23. PrimEx @ High Energies with EIC Precision Measurement of → decay width • All  decay widths are calculated from  decay width and experimental Branching Ratios (B.R.): Γ(η→ decay) = Γ(→) × B.R. • Any improvement in Γ(→) will change the whole - sector in PDB 23

24. Determination of quark mass ratio There are two ways to determine the quark mass ratio: • Γ(η→3π) is the best observable for determining the quark mass ratio, which is obtained from Γ(η→γγ) and known branching ratios: • The quark mass ratio can also be given by a ratio of meson masses:

25. Determination of quark mass ratio Γ(η→3)=Γ(→)×B.R. 25

26. Mixing Angles • Mixing corrections: • Decayconstant corrections: Γ(η/η´→γγ) widths are crucial inputs for obtaining fundamental mixing parameters.

27. Summary • It looks possible to perform high precision transition form factor measurements of light pseudoscalar mesons at low Q2 with EIC at high energies • Extrapolation to Q2=0 will define the radiative decay widths: Γ(0→), Γ(→), Γ(’→) • Fundamental input to Physics: • precision test of chiral anomaly predictions • 0, and ’ interaction electromagnetic radii • extraction of Ο(p6) low-energy constant in the chiral Lagrangian • determination of quark mass ratio • -’ mixing angle • is the ’ an approximate Goldstone boson? 27

28. The End Hall D, March 7, 2008 28

29. ρ, ω The Primakoff Effect Challenge: Extract the Primakoff amplitude 29

30. (0→)World Data • 0 is lightest quark-antiquark hadron • The lifetime:  = B.R.( 0 →γγ)/(0 →γγ) 0.8 x 10-16 second ±1% • Branching ratio: B.R. ( 0→γγ)= (98.8±0.032)% 0→ 30

31. Estimated Systematic Errors 31

32. Electromagnetic Calorimeter: HYCAL • Energy resolution • Position resolution • Good photon detection efficiency @ 0.1 – 5 GeV; • Large geometrical acceptance PbWO4 crystals resolution Pb-glass budget HYCAL only Kinematical constraint

33. Beam Time and Statistics • Target: L=20 cm, LHe4 NHe = 4x1023 atoms/cm2 Nγ = 1x107 photon/sec (10-11.5 GeV part) <Δσ(prim.)> = 1.6x10-5 mb N() = NHexNγx<Δσ>xεx(BR) = 4x1023x 1x107x 1.6x10-32x0.7x0.4 = 64 events/hour = 1500 events/day = 45,000 events/30 days • Will provide sub-percent systematic error 15 Days