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Karl Slifer University of New Hampshire

This talk provides a brief review of the physics motivation for g2p (E08-027) experiment, focusing on the installation, experimental run status, and online analysis results. Key topics include kinematic variables, structure functions, inclusive cross section, and compositeness of target, along with discussions on the violation of sum rules and neutron polarizabilities. Relevant experimental techniques, new data on neutron polarizabilities, and applications to bound state quantum electrodynamics (Q.E.D.) are also discussed. The talk addresses the structure dependence of hydrogen hyperfine splitting and spectroscopic measurements of muonic hydrogen, highlighting discrepancies in proton charge radius results. Various experts' comments on the significance and implications of these findings are included.

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Karl Slifer University of New Hampshire

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  1. The g2p Experiment Jefferson Lab User Group Meeting 6/5/2012 Karl Slifer University of New Hampshire

  2. This talk Brief review of Physics Motivation for g2p (E08-027) Review of the Installation and Experimental Run Status of the Analysis Online Results

  3. Detectors E’ scattered E Incident beam Target Target “shrapnel” not detected Important Kinematic Variables Q2 = Momentum transfer squared W = Invariant Mass of target System Bjorken variable

  4. Inelastic Scattering E’ E 1st order Feynman diagram q ° * W P Spin-1/2 Target Inclusive Cross Section Compositeness of target characterized by the Structure Functions

  5. Inelastic Scattering E’ E 1st order Feynman diagram q ° * W P Spin-1/2 Target Inclusive Polarized Cross Section Two additional Structure Functions needed

  6. Experimental Technique − −

  7. Proton g2 data from SLAC Q2 ≈ 5 GeV2 x2g2

  8. Proton g2 data from SLAC Q2 ≈ 5 GeV2 x2g2 Leading Twist Precision does not allow unambiguous HT extraction

  9. Proton g2 data from JLAB SANE Q2 ≈ 3-6 GeV2 Leading Twist Very Prelim Stat Errors x2g2

  10. RSS Experiment (Spokesmen: Rondon and Jones) Q2 = 1.3 GeV2 (proton) consistent with zero => low x HT are small in proton. non-zero by 2.6s =>Significant HT at low x needed to satisfy Neutron BC sum rule. (neutron) K.S., O. Rondon et al. PRL 105, 101601 (2010)

  11. BC Sum Rule H.Burkhardt and W.N. Cottingham Annals Phys. 56 (1970) 453. Assumptions: the virtual Compton scattering amplitude S2 falls to zero faster than 1/x g2 does not behave as d(x) at x=0. Discussion of possible causes of violations R.L. Jaffe Comm. Nucl. Part. Phys. 19, 239 (1990) “If it holds for one Q2 it holds for all”

  12. BC Sum Rule 0<x<1 P BC satisfied w/in errors for JLab Proton 2.8 violation seen in SLAC data Mostly unmeasured N 3He

  13. Generalized Spin Polarizabilities

  14. Forward Spin Polarizabilities Neutron PRL 93: 152301 (2004) Dramatic Failure of ChiPT • Relativistic Baryon ÂPT • Bernard, Hemmert, Meissner • PRD 67:076008(2003) • Heavy Baryon ÂPT Calculation • Kao, Spitzenberg, Vanderhaeghen • PRD 67:016001(2003)

  15. New Data on the Neutron Polarizabilities Plots courtesy of V. Sulkosky

  16. New Data on the Neutron Polarizabilities Large discrepency with dLT remains Plots courtesy of V. Sulkosky

  17. Proton g0 Calculations also fail for proton g0 Proton PLB672 12, 2009

  18. LT Spin Polarizability Kochelev & Oh. arxiv:1103.4892. (2011) Improves agreement with neutron, Neutron

  19. LT Spin Polarizability Kochelev & Oh. arxiv:1103.4892. (2011) Improves agreement with neutron, Proton Neutron No data yet on proton LT polarizability

  20. Applications to Bound State Q.E.D. nucleus ≈ 10-15 Atom ≈ 10-10 The finite size of the nucleus plays a small but significant role in atomic energy levels.

  21. Applications to Bound State Q.E.D. Hydrogen HF Splitting nucleus ≈ 10-15 Atom ≈ 10-10 The finite size of the nucleus plays a small but significant role in atomic energy levels.

  22. Applications to Bound State Q.E.D. Hydrogen HF Splitting nucleus ≈ 10-15 Atom ≈ 10-10 The finite size of the nucleus plays a small but significant role in atomic energy levels. Friar & Sick PLB 579 285(2003)

  23. Structure dependence of Hydrogen HF Splitting Elastic Scattering DZ=-41.0±0.5ppm

  24. Structure dependence of Hydrogen HF Splitting Nazaryan,Carlson,Griffieon PRL 96 163001 (2006) Inelastic DZ=-41.0±0.5ppm Dpol≈ 1.3±0.3 ppm Elastic piece larger but with similar uncertainty 0.2265 ppm integral of g1 & F1 pretty well determined from F2,g1 JLab data

  25. Structure dependence of Hydrogen HF Splitting Nazaryan,Carlson,Griffieon PRL 96 163001 (2006) Inelastic Dpol≈ 1.3±0.3 ppm Elastic piece larger but with similar uncertainty 0.2265 ppm weighted heavily to low Q2

  26. Hydrogen Hyperfine Structure E08-027 assuming CLAS model with 100% error Integrand of ¢2 Dominated by this region due to Q2 weighting

  27. Hydrogen Hyperfine Structure E08-027 assuming CLAS model with 100% error Integrand of ¢2 But, unknown in this region: Dominated by this region due to Q2 weighting MAID Model Simula Model So 100% error probably too optimistic E08-027 will provide first real constraint on D2

  28. PSI measurement of the RMS proton radius Spectroscopic measurement of the energy splitting of the 2S1/2-2P1/2 levels in muonic hydrogen (Lamb shift).

  29. Proton Charge Radius from mP lamb shift disagrees with eP scattering result by about 6% <Rp> = 0.84184 ± 0.00067 fm Lamb shift in muonic hydrogen <Rp> = 0.897 ± 0.018 fm World analysis of eP scattering <Rp> = 0.8768 ± 0.0069 fm CODATA world average R. Pohl et.alNature, July 2010 I. Sick PLB, 2003 I. Sick (Basel) : “What gives? I don’t know”. “Serious discrepency” [ELBA XI, Nature.com] C. Carlson (W&M) : “Something is missing, this is very clear.” [Nature.com] P. Mohr (NIST) : “would be quite revolutionary.” [L.A. Times.] B. Odom (N.Western) : “...very surprised to find strong disagreement.” [N.P.R.] J. Flowers (N.P.L.) “...could mean a complete rethink of QED”. [National Geographic] “...opens door for a theorist to come up with next[NY Times] theoretical leap, and claim their Nobel prize”.

  30. Polarizability : Integrals of g1 and g2 weighted by 1/Q4 Zemach radius : Integral of GEGM weighted by 1/Q2 Dominated by Kinematic region of E08-027 and E08-007

  31. E08-027 : Proton g2 Structure Function A. Camsonne J.P. Chen D. Crabb K. Slifer • Primary Motivation • Proton g2 structure function has never been measured at low or moderate Q2. • We will determine this fundamental quantity at the lowest possible Q2 • This will help to clarify several outstanding puzzles • Hydrogen HyperFine Splitting : Lack of knowledge of g2 at low Q2 is one of the leading uncertainties. • Proton Charge Radius : also one of the leading uncertainties in extraction of <Rp> from m-H Lamb shift.

  32. Experimental Technique Inclusive Polarized Cross Section differences Major Installation in Hall A Polarized proton target upstream chicane downstream local dump Low current polarized beam Upgrades to existing Beam Diagnostics to work at 85 nA Lowest possible Q2 in the resonance region Septa Magnets to detect forward scattering

  33. Major New Installation in Hall A

  34. A few minor mechanical setbacks • delayed the start of the experiment by 149 days • Redesigned/Replaced/Repaired • Polarized target magnet • Chicane bellows • Right Septa Magnet • Both Septa Max Field • Local Dump Cooling • Harp wires

  35. A few minor mechanical setbacks • delayed the start of the experiment by 149 days • Redesigned/Replaced/Repaired • Polarized target magnet • Chicane bellows • Right Septa Magnet • Both Septa Max Field • Local Dump Cooling • Harp wires Lab Support in dealing with these issues has been Greatly Appreciated! Grad Student and Post-Doc response also amazing

  36. Kinematic Coverage Reduced kinematics Mp < W < 2 GeV 0.02 < Q2 < 0.2 GeV2

  37. Projections LT Spin Polarizability BC Sum Integral G2

  38. Elastic Scattering, Form factors are normalized such that: Charge Magnetic moment

  39. FF’s represent the momentum-space charge and magnetization distributions =>fourier transforms of the coordinate space distributions. (non-rel limit). Expansion at low Q2 gives RMS charge radius the slope of GE at Q2=0 determines the “size” of the proton.

  40. Proton GE Data at low Q2 GE/GD <Rp> = 0.897 ± 0.018 fm Best value of <Rp> from elastic proton scattering I. Sick PLB 2003 Normalized to the dipole form Latest world analysis (Unpublished) <Rp> = 0.870 +- 0.010 fm

  41. E08-007 : GE/GM G. Ron*, D. Higintbothan, R. Gilman J. Arrington, A. Sarty, D. Day Super-ratio of left/right Asymmetries:

  42. Projected Results

  43. Online Results 2.2 GeV, 90 degrees at 2.5T : about 3.8E9 inelastic triggers recorded 1.7 GeV, 90 degrees at 2.5 T : about 3.2E9 inelastic triggers recorded <PT>+ = 30%@ 2.5T <PT> = 75% @ 5T DAQ Rate 6-7kHz with less than 30% Deadtime

  44. Polarized Ammonia Target Dynamic Nuclear Polarization of NH3 Has performed remarkably well after target group transplanted the Hall B coil package 5 T/ 140 GHz or 2.5 T/70 GHz operation Helmholtz superconduct magnet 1K 4He evaporation refrigerator Cooling power: about 1 W Microwave Power >1W at 140 GHz Insulated cryostat 85 L Liquid He resevoir 57 L Liquid N shield (300K BB shield)

  45. Polarized Ammonia Target Dynamic Nuclear Polarization of NH3 Has performed remarkably well after target group transplanted the Hall B coil package NH3 Empty CH2 NH3 Dummy Carbon

  46. Online Polarimetry Average Polarization >30% at 2.5 Tesla/70 GHz courtesy James Maxwell

  47. Online Polarimetry Decay with accumulated dose was very slow at 2.5T. courtesy James Maxwell

  48. Online Polarimetry Average Polarization >75% at 5.0 Tesla/140 GHz courtesy James Maxwell

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