1. 11 Primakoff Experiments with EIC A. Gasparian NC A&T State University, Greensboro, NC For the PrimEx Collaboration Outline  Physics motivation:  The first experiment at JLab:  0 lifetime  Development of precision technique  Results for  0 lifetime  Experiments with EIC  Summary

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

3. 3 Fate of QCD Symmetries

4. 4 Chiral SU L (3)XSU R (3) spontaneously broken Goldstone mesons π 0, η 8 Chiral anomalies Mass of η 0 P →γγ ( P: π 0, η, η ׳ ) Quark flavor SU(3) breaking The mixing of π 0, η and η ׳ The  0, η and η’ system provides a rich laboratory to study the symmetry structure of QCD at low energy. Lightest Pseudoscalar Mesoms

5. 55 The PrimEx Experimental Project Experimental program Precision measurements of:  Two-Photon Decay Widths: Γ(  0 →  ), Γ(  →  ), Γ(  ’ →  )  Transition Form Factors at low Q 2 (0.001-0.5 GeV 2 /c 2 ): F(  * →  0 ), F(  * →  ), F(  * →  ) Test of Chiral Symmetry and Anomalies via the Primakoff Effect

6. 66 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?

7. 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%  Precision measurements of  (  0 →  ) at the percent level will provide a stringent test of a fundamental prediction of QCD.  0 →   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%

8. 8 Decay Length Measurements (Direct Method)     1x10 -16 sec  too small to measure solution: Create energetic  0 ‘s, L = v   E  /m  But, for E= 1000 GeV, L mean  100 μm very challenging experiment  Measure  0 decay length 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. 9 e + e - Collider Experiment  e + e -  e + e -  *  *  e + e -  0  e + e -   e +, e - scattered at small angles (not detected)  only  detected  DORIS II @ DESY  Results: Γ(  0  ) = 7.7 ± 0.5 ± 0.5 eV ( ± 10.0%)  Not included in PDG average  Major limitations of method  knowledge of luminosity  unknown q 2 for  *  *  0 → 

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

11. 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. 12 PrimEx Experiment at Hall B JLab  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)  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

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

14. 14L. GanAPS, April 15, 200814 Estimated Systematic Errors Contributions Errors Photon flux1.0% Target number0.1% Background subtraction0.9% Event selection0.5% HYCAL response function0.5% Beam parameters0.4% Acceptance0.3% Model errors (theory)0.25% Physics background0.24% Branching ratio (PDG)0.03% Total1.6%

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

16. 16 Next Run 16

17. 17 PrimEx @ High Energies with EIC Experimental program Precision measurements of:  Transition Form Factors at low Q 2 (0.001-0.5 GeV 2 /c 2 ): F(  * →  0 ), F(  * →  ), F(  * →  )

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

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

20. 20  Direct measurements of slopes: F(  * →  0 ), F(  * →  ), F(  * →  )  Interaction radii: F γγ *P (Q 2 ) ≈ 1 - 1/6 ▪ P Q 2  ChPT for large N c predicts relation between the slopes.  Extraction of Ο(p 6 ) low-energy constant in the chiral Lagrangian  Extraction of decay widths: Γ(  0 →  ), Γ(  →  ), Γ(  ’ →  )  Precision test of chiral anomaly predictions Transition Form Factors at Law Q 2

21. 21 Experimental Status for Experimental Status for F(  * →  0 ) F(  * →  0 ) ≈ 1 – a  Q 2 /m 2 

22. 22 Experimental Status for Experimental Status for F(  * →  )

23. 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 will change the whole  - sector in PDB  - sector in PDB

24. 24 There are two ways to determine the quark mass ratio: Γ( η→ 3 π ) 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: The quark mass ratio can also be given by a ratio of meson masses: Determination of quark mass ratio

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

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

27. 27 Summary  Extrapolation to Q 2 =0 will define the radiative decay widths: Γ(  0 →  ), Γ(  →  ), Γ(  ’ →  )  It looks possible to perform high precision transition form factor measurements of light pseudoscalar mesons at low Q 2 with EIC at high energies  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?

28. 28A. GasparianHall D, March 7, 200828 The End

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

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

31. 31 Estimated Systematic Errors Contributions Errors Photon flux1.0% Target number0.1% Background subtraction0.9% Event selection0.5% HYCAL response function0.5% Beam parameters0.4% Acceptance0.3% Model errors (theory)0.25% Physics background0.24% Branching ratio (PDG)0.03% Total1.6%

32. 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. 33 15 Days Beam Time and Statistics  Target: L=20 cm, LHe4 N He = 4x10 23 atoms/cm 2 N γ = 1x10 7 photon/sec (10-11.5 GeV part) = 1.6x10 -5 mb N(  ) = N He xN γ x 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