1. Precision Measurements of Electromagnetic Properties of  0, η and η’ Mesons at JLab A. Gasparian NC A&T State University, Greensboro, NC and the PrimEx Collaboration Outline  The project and physics motivation:  The first experiment:  0 lifetime  Results for the  0 lifetime  PrimEx at 12 GeV  The proposed  →  experiment with GlueX  Summary

2. 2 chiral limit: is the limit of vanishing quark masses m q → 0. QCD classical Lagrangian with quark masses set to zero: Has Large global symmetry group: The QCD Lagrangian A. GasparianINT 09-3, November 12, 2009

3. A. GasparianINT 09-3, November 12, 20093 Physics Motivation

4. A. GasparianINT 09-3, November 12, 20094 Physics Motivation (contin.) Fundamental input to Physics:  precision tests of chiral anomaly  determination of quark mass ratio   -  ’ mixing angle   0,  and  ’ interaction electromagnetic radii  is the  ’ an approximate Goldstone boson?

5. A. GasparianINT 09-3, November 12, 20095 The PrimEx 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. A. GasparianINT 09-3, November 12, 2009 Transition Form Factors at Low Q 2  Direct measurement of slopes Interaction radii: F γγ*P (Q 2 )≈1-1/6 ▪ P Q 2 ChPT for large N c predicts relation between the three slopes. Extraction of Ο(p 6 ) low-energy constant in the chiral Lagrangian  Input for light-by-light scattering for muon (g-2) calculation  Test of future lattice calculations 6

7. A. GasparianINT 09-3, November 12, 20097  0  Decay Width (the First Experiment)   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: <1%  K. Kampf, B. Moussallam, PRD 79, 076005, 2009  Precision measurements of  (  0 →  ) at the percent level will provide a stringent test of a fundamental prediction of QCD.  QCD sum rule calculations: (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  for E= 1000 GeV, L mean  100 μm very challenging experiment  Measure  0 decay length Recent CERN experiment, 1984: 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 →  A. GasparianINT 09-3, November 12, 2009

9. A. GasparianINT 09-3, November 12, 20099 Primakoff Method ρ,ωρ,ω Challenge: Extract the Primakoff amplitude 12 C target Primakoff Nucl. Coherent Interference Nucl. Incoh.

10. A. GasparianINT 09-3, November 12, 200910 PrimEx Experiment  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

11. A. GasparianINT 09-3, November 12, 200911 PrimEx-I Milestones  Proposal approved in 1999 by PAC15, re-approved by PAC22 (E02-103) in 2002 with A rating.  In 2000, NSF awarded a collaborative MRI grant of $1 M to develop the experimental setup.  Installation of setup in August, 2004.  Commissioning: September, 2004 (10-15 days)  Data taking: September-November (45 days)  data on two targets: 12 C 208 Pb,  Total number of π 0 ~3.2 M  Total elastic π 0 : ~ 300 K  Total Primakoff π 0 : ~ 3-5 K  First preliminary results released at the April, 2007 APS meeting with AIP press conference.  Publication of results is expected this winter

12. A. GasparianINT 09-3, November 12, 200912 PrimEx-I Experiment We measure:  initial photon energy: E  and time  energies of decayed photons: E  1, E  2 and time  X,Y positions of decayed photons Kinematical constrains:  Conservation of energy;  Conservation of momentum;  m  invariant mass PrimEx commissioned and took data: August-November, 2004

13. A. GasparianINT 09-3, November 12, 200913  0 Event selection elastic non-  0 backgroundInelastic  0 s(background) elastic  0 s(signal)  Tagger-HyCal timing ( Δt) ;  Energy conservation: Elasticity ((E γ1 +E γ2 )/E tagger )  Invariant mass (M γγ ) ;

14. A. GasparianINT 09-3, November 12, 200914 Fit to Extract  0  Decay Width  Theoretical angular distributions smeared with experimental resolutions are fit to the data Γ(  0  )  7.82 eV  2.2% (stat. error, including fit error)

15.  Independent verifications of the extracted cross sections are needed  The sources of Systematic Errors:  Instrumental (experimental setup)  Model errors (from fit)  The data for the following QED processes had been taken periodically in this experiment:  e + e - pair production  Compton scattering A. Gasparian15INT 09-3, November 12, 2009 Systematic Errors in  (  0 →  )

16. A. GasparianINT 09-3, November 12, 200916 Control of Systematic Errors: Compton Cross Section Δσ/ΔΩ (mb/6.9 msrad)  Average stat. error: 0.6%  Average syst. error: 1.5%  Total error: 1.6%  Cross sections are in agreement with theory at percent level

17. A. GasparianINT 09-3, November 12, 200917 Model Errors in Fitting Procedure  Primakoff: magnitude kept free; form factor is calculated  Nucl. Incoherent: magnitude kept free; form factor is calculated  Interference: Phase angle kept free;  Nucl. Coherent: magnitude kept free; form factor is calculated

18. A. GasparianINT 09-3, November 12, 200918 Γ(  0  ) Model Sensitivity  Incoherent Production  A →  0  A´  Two independent approaches:  Glauber theory  Cascade Model (Monte Carlo)  Photon shadowing effect Deviation in Γ(  0  ) less than 0.2%  Overall model error in Γ(  0  ) extraction is controlled at 0.3%

19. A. GasparianINT 09-3, November 12, 200919 Estimated Systematic Errors Contributions Error, [%] Photon flux1.0 Target0.1 Yield extraction1.6 HYCAL eff.0.5 Beam parameters0.4 Trigger eff.0.1 VETO eff.0.4 Acceptance0.3 Model errors (theory)0.3 Physics background 0.25 Branching ratio 0.03 Total2.1

20. A. GasparianINT 09-3, November 12, 200920 Final Result from PrimEx-I

21. A. GasparianINT 09-3, November 12, 200921 Planned PrimEx-II ExperimentContributions Error, [%] Photon flux1.0 Target0.1 Yield extraction0.5 HYCAL eff.0.2 Beam parameters0.4 Trigger eff.0.1 VETO eff.0.3 Acceptance0.3 Model errors (theory)0.3 Physics background 0.25 Branching ratio 0.03 Total (syst.) 1.3  Statistical error: 0.44% Projected PrimEx-II (1.4%)

22. A. GasparianINT 09-3, November 12, 200922 Proposed Experiment for  →  Decay Width Measurement in Hall D   all-decay widths are normalized to  decay width and experimental Branching Ratios (B.R.): Γ(η → all-decays) =Γ(  →  )/B.R.  Improvement in Γ(  →  ) will change the whole  -sector in PDG  We propose to measure Γ(  →  ) with 3% total error using GlueX standard setup

23. A. GasparianINT 09-3, November 12, 200923  →  Decay Width Experiments: e + e - Collider Results  e + e -  e + e -  *  *  e + e - η  e + e -   e +, e - scattered at small angles (not detected);  Only  detected;  PDG average for collider experiments: Γ(η  ) = 0.510 ± 0.026 keV ( ± 5.1%)  Error in individual experiments: from 7.6% to 25%  Major limitations of method  unknown q 2 for  *  *  knowledge of luminosity η → 

24. A. GasparianINT 09-3, November 12, 200924 The Primakoff Method ρ,ωρ,ω Challenge: Separate Primakoff amplitude from hadronic processes. η  larger momentum transfer:  Difficulties of  →  experiment:  cross section is smaller  larger overlap between Primakoff and hadronic processes We propose to use hydrogen and 4 He targets to address all those issues.

25. A. GasparianINT 09-3, November 12, 200925 Cornell Primakoff Experiment  Cornell (PRL, 1974)  brems.  beam, E  =5.8, 9.0, 11.45 GeV  targets: Be, Al, Cu, Ag, U  Result:  ( η  )=(0.324  0.046) keV (  14.2%)

26. 26A. GasparianINT 09-3, November 12, 200926 Proposed  Experiment with GlueX Standard Setup  The GlueX setup will provide:  High energy tagged photon beam E γ =10 – 11.7 GeV  High acceptance FCAL calorimeter  LH2 and LHeTargets (30 cm)  Pair Spectrometer  Dedicated Run with:  5 mm diameter beam line collimator  amorphous radiator (~10 -4 R.L.Au)  small detector behind the FCAL for overall control of systematic errors 75 m Counting House

27. 27A. GasparianINT 09-3, November 12, 200927 Proposed  Experiment with GlueX Standard Setup (contn.)

28. 28A. GasparianINT 09-3, November 12, 200928 Photon Flux Stability and Resolutions  5.0 mm collimator  double the tagging efficiency from 15% to ~30%  help to control photon flux stability within 1% Design limit 5.0mm coll. Designed limit  Angular resolution vs. collimator diameter

29. 29A. GasparianINT 09-3, November 12, 200929 Acceptances and Resolutions Our interest Acceptance of FCAL vs. prod. angle Designed length Angular resolution vs. target length

30. A. GasparianINT 09-3, November 12, 200930 Statistics and Beam Time Request LH 2 target40 days 4 He target30 days Empty target run6 days Tagger efficiency, TAC4 days Setup calibration and checkout 8 days Total88 days  Target: 30 cm (3.46% r.l.) LH 2, Np=1.28x10 24 p/cm 2  Photon intensity: 7.6x10 6 γ /sec in E γ = 10.5–11.7 GeV  Total cross section on P for θ η =0 - 3.5 0, Δσ = 1.1x10 -5 mb (10% is Primakoff).  N(evts) = N p x N γ x Δσ x ε(eff.)x(Br. Ratio) = 1.28x10 24 x7.6x10 6 x1.1x10 -32 x0.7x0.4 = 3.0 x 10 -2 events/sec = 2592 events/day = 259 Primakoff events/day  Statistics: 1% stat. error on each LH 2 and LHe4 target  Beam time request:

31. A. GasparianINT 09-3, November 12, 200931 Estimated Error Budget Contributions Estimated Error Photon flux1.0% Target number0.5% Background subtraction1.8% Event selection1.7% Acceptance, misalign.0.5% Beam energy0.2% Model error0.3% Branching ratio (PDG) 0.66% Total Systematic2.8% Statistical error1.0% Systematic error2.8% Total Error3.0%  Systematical errors:  Total estimated error:

32. A. GasparianINT 09-3, November 12, 200932 The Expected Result for  →  Decay Width   all-decay widths are normalized to  decay width and experimental Branching Ratios (B.R.): Γ(η → all-decays) =Γ(  →  )/B.R.  Improvement in Γ(  →  ) will change the whole  -sector in PDG  We propose to measure Γ(  →  ) with 3% total error using GlueX standard setup

33. A. GasparianINT 09-3, November 12, 200933 Physics Outcome from  Experiment Γ(η → 3  )=Γ(  →  )×B.R.  (  -  ’) mixing angle:  light quark mass ratio

34. Summary and Outlook A. Gasparian34INT 09-3, November 12, 2009  PrimEx-12 experimental program has been developed to perform precision tests of chiral symmetry and anomaly effects in the light pseudoscalar meson sector.  The first experiment, the  0 decay width measurement, has been performed in fall, November 11, 2009November 11, 20092004 in Hall B with 6 GeV beam.  (  0  ) has been extracted with high precision at 3% level. A new PrimEx-II run is approved to reach the projected 1.4% precision.  New Primakoff high precision experiment for Г(  →  ) in Hall D will:  Potentially solve the discrepancy between collider and Primakoff results;  Improve all  decay widths in PDG by more than a factor of 2;  Determine the light quark mass ratio in model independent way;  Significantly improve the (  -  ’) mixing angle determination.  The model error in hadronic contributions in decay width extraction process is currently controlled on 0.5% level for light and medium nuclei.  Availability of modern tagged-photon beams and novel calorimetry made the Primakoff method a feasible tool to reach the required few percent accuracy in radiative decay width measurements.  The GlueX experimental facility with its high resolution and high intensity 12 GeV photon tagger with high aperture FCAL calorimeter, is well suited for the Г(  ) Primakoff measurement with a 3% precision.  A proposal for  η/  experiment is being develop using the GlueX setup with 12 GeV.

35. The End A. GasparianINT 09-3, November 12, 200935

36. Cross section on Proton A. GasparianINT 09-3, November 12, 200936

37. A. GasparianINT 09-3, November 12, 200937 Γ(  0  ) Model Sensitivity (an Example) Variations in shadowing parameter   ΔΓ  < 0.1%  F A – Nuclear Form Factor  F I – Intermediate state contribution   - Shadowing parameter

38. A. GasparianINT 09-3, November 12, 200938  0 Forward Photoproduction off Complex Nuclei: (theoretical models)  Coherent Production  A →  0  A PrimakoffNuclear coherent  0 rescattering Photon shadowing Leading order processes: (with absorption) Next-to-leading order: (with absorption)