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Charge asymmetry and symmetry properties

Charge asymmetry and symmetry properties. Egle Tomasi-Gustafsson IRFU, SPhN-Saclay, and IN2P3-IPNO France. DUBNA, September 1-5, 2009. e -. e -. e +. p. q 2 >0. q 2 <0. p. e -. p. p. Scattering and annihilation. Asymptotics - QCD - analyticity. Space-like. (+). (+).

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Charge asymmetry and symmetry properties

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  1. Charge asymmetry and symmetry properties Egle Tomasi-Gustafsson IRFU, SPhN-Saclay, and IN2P3-IPNO France DUBNA, September 1-5, 2009 Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  2. e- e- e+ p q2>0 q2<0 p e- p p Scattering and annihilation Asymptotics - QCD - analyticity Space-like (+) (+) Time-like p+p ↔ e++e- +p Unphysical region _ _ q2=4mp2 q2 e+p  e+p p+p ↔ e++e- Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  3. Crossing Symmetry Scattering and annihilation channels: - Described by the same amplitude : - function of two kinematical variables, sandt - which scan different kinematical regions k2→ – k2 p2 p2→ – Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  4. 1g-2g interference M. P. Rekalo, E. T.-G. and D. Prout, Phys. Rev. C60, 042202 (1999) 2g 1g { { 1{g Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  5. Symmetry relations (annihilation) • Differential cross section at complementary angles: The SUM cancels the 2g contribution: The DIFFERENCE enhances the 2g contribution: Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  6. Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  7. Radiative Return (ISR) e+ +e- p + p +  B. Aubert ( BABAR Collaboration) Phys Rev. D73, 012005 (2006) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  8. Angular distribution 1.877÷1.950 1.950÷2.025 2.025÷2.100 Events/0.2 vs. cos q 2.100÷2.200 2.200÷2.400 2.400÷3.000 • 2g-exchange? Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  9. Mpp=1.877-1.9 A=0.01±0.02 Mpp=2.4-3 E. T.-G., E.A. Kuraev, S. Bakmaev, S. Pacetti, Phys. Lett. B (2008) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  10. Linearity of the Rosenbluth fit Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  11. Parametrization of 2g-contribution for e+p From the data: deviation from linearity << 1%! E. T.-G., G. Gakh, Phys. Rev. C 72, 015209 (2005) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  12. 2γ-Gamma Models and Data C. Perdrisat,L. Pentchev Expt. Jlab 04-019 measured Ratio PL/PT for Q2=2.49 GeV2 at 3 values of ε PRELIMINARY NO ε-dependence at 0.01 level NO evidence of 2g contribution The inclusion of hard 2γ exchange: Chen et al (2003) with GPDs, Blunden et al (2003) in hadronic model Bystriskyi et al., LSF PR C75, 015207 (2007) 8/23/2014 12 Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  13. Linear fit to e+4He scattering Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  14. Electron/Positron scattering • What about data: electron positron scattering (elastic or inelastic) in the same experimental conditions? • If R ≠1 is there any other source of asymmetry? • Any evidence of two photon exchange (real part of hard box diagram)? Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  15. Electron/Positron scattering Two photon exchange: Born approximation 2g exchange: Asymmetry The effect is enhanced in the ratio Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  16. World data e+e- scattering Fitting with a constant R=0.997 DR=0.003 c2 =1.03 Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  17. Elastic scattering q2 =1, 3, 5 GeV2 e=0.2, 0.5, 0.8 R=(-0.071 ± 0.016 )e +(1.058±0.014) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  18. Electron/Positron scattering E.A. Kuraev, V.V.Bytev, S.Bakmaev and E.T-G, PRC 78, 015295 (2008). C=0.97,0.99 e=0.4 q2=3 GeV2 2g exchange Soft photon emission Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  19. Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  20. c2=1.1 c2=4. Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  21. Simulation with PANDA p+p e++ e- Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  22. N=a0+a2cosq sin2q+a1 cos2q, a2~2g 1g 2g 0.02 q2=5.4 GeV2 2g 0.2 2g 0.05 Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  23. Conclusions • Determination of the validity of one photon exchange approximation: basic question for deriving information on the hadron structure • in annihilation processes all information is contained in a precise measurement of the angular distribution • Comparison of scatteringand annihilation channels: model independent statements • No evidence of two photon exchange (real part) in the data. • Precise calculation of radiative corrections Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  24. Simulations q2=5.4,8.2,13.8 GeV2 Main effect: odd cosq - distribution • Approximations: • Neglect contributions to GE,GM • Consider only real part Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  25. N=a0+a2cosq sin2q+a1 cos2q, a2~2g 2g visible from F3/GM ~ 0.05 Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  26. Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  27. Fitting the angular distributions.. The form of the differential cross section: is equivalent to: Cross section at 900 Angular asymmetry E. T-G. and M. P. Rekalo, Phys. Lett. B 504, 291 (2001) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  28. Angular asymmetry andCharge asymmetry Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  29. Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  30. Inelastic e+e- scattering R=1.002±0.002 R=(-0.0009 ± 0.001 )q2 +(1.005±0.003) R=(0.005 ± 0.014 )XBj +(1.002±0.004) c2=0.84 Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  31. Elastic e -4He scattering ( L.J. Kaufman) Ayexp(4He) =-13.51 ± 1.34 (stat) ± 0.37(syst) ppmq=6°, Q2=0.077 GeV2  Im F1 (s,q2) ~F(q2) If Im F1 (s,q2) ~ Re F1 (s,q2) 1g ~ 2g term ! Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  32. Matrix element: spins 0 and 1/2 Two helicity amplitudes, functions of s and t ~m q1+q2 F(0)=Ze Electromagnetic He form factor Holds for crossed channel, q1→ -q1 q2→ -q2 Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  33. Two photon exchange • The calculation of the box amplitude requires the description of intermediate nucleon excitation and of their FFs at any Q2 • Different calculations give quantitatively different results Theory not enough constrained! Model independent statements Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  34. Model independent statements In presence of 2g exchange : • Non linearityin the Rosenbluth fit • - charge asymmetry • (and/or odd powers of cosq) • in the crossed channel • Non vanishing odd polarization observables • Different cross section for electron/positron – proton elastic(inelastic) scattering M. P. Rekalo, E. T.-G. , EPJA (2004), Nucl. Phys. A (2003) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  35. Unpolarized cross section Two photon exchange p2 p1 q Lab system F1~m, F~a0, f~a Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  36. Transversal Beam asymmetry(2g exchange) Normal component Spin vector of e beam T-odd ,~m, imaginary part of the spin flip 2g amplitude If ground state He,predicted: Ayth~10 -10 E.D. Cooper, C.J. Horowitz, PRC72,034602 (2005) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  37. Elastic e -4He scattering ( L.J. Kaufman) Ayexp(4He) =-13.51 ± 1.34 (stat) ± 0.37(syst) ppmq=6°, Q2=0.077 GeV2 → contibution from excited states… Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  38. Two photon exchange • The calculation of the box amplitude requires the description of intermediate nucleon excitation and of their FFs at any Q2 • Different calculations give quantitatively different results Theory not enough constrained! Model independent statements Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  39. How to proceed? Our Suggestion: • Search for model independent statements • Exact calculation in frame of QED (p~m) • Prove that QED box is upper limit of QCD box diagram Our Conclusion • Two photon contribution is negligible (real part) • Radiative corrections are huge: take into account higher order effects (Structure Functions method) E.A. Kuraev, Yu. Bystritsky, V. Bytev, E. T.-G. , (2006-2008) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  40. 1g-2g interference (e-d) D/A C/A M. P. Rekalo, E. T-G and D. Prout, Phys. Rev. C60, 042202 (1999) Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

  41. Unpolarized cross section • Induces four new terms • Odd function of q: • Does not contribute at q =90° Two Photon Exchange: Egle TOMASI-GUSTAFSSON CEA DSM IRFU SPhN and CNRS/IN2P3/ IPNO

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