The Form Factors of the Nucleons: Present Status - Fisica

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Nucleon Form Factors Form factors have been obtained from elastic electron scattering cross sections from the very beginning of R. Hofstadter’s pioneering work at Stanford in the mid-1900s. In early 70’s the data available suggested that G Ep decreased faster than the dipole form factor G D=(1+Q 2 /0.71) -2 (see figure). The first experiment to show a strong preference for G Ep/G D ~ 1 was that of Litt et al. published in 1970, not included in this figure. Following experiments mostly confirmed the Litt results (Walker et al. 1994, Andivahis et al, 1994)) including two experiments at Jlab (Christy et al 2004, and Qattan et al. 2005). 2/17/2013 C.F. Perdrisat SAEMP Trento 2013 2
Results for the proton’s G Ep and G Mp form factors had reached apparent stability by 1990’s, indicating that “scaling”, i.e. the fact that G Ep/G D, G Mp/μ pG D are approximately independent of Q 2 , and ≈1, may be true. In the late 1990s it became experimentally feasible to obtain the nucleon form factors from double-polarization experiments, also based on the assumption of single photon exchange, or Born approximation, as had been first suggested by Akhiezer and Rekalo in the late sixties. Spectacular experimental progress in measuring G E/G M followed the opening of Jefferson Lab, for both proton and neutron. Our understanding of the shape, and charge and current distributions in the nucleon has increased considerably, and changed drastically. New information on hadron structure, such as role of quark orbital angular momentum, transverse charge density distribution, dressed quark form factor has followed in short order. 2/17/2013 C.F. Perdrisat SAEMP Trento 2013 3
Page 1: The Form Factors of the Nucleons: P
Page 5 and 6: One-photon exchange or Born approxi
Page 7 and 8: Rosenbluth Separation Method In ter
Page 9 and 10: All Rosenbluth separation data for
Page 11 and 12: Polarization Transfer Method h beam
Page 13 and 14: Results for the G Ep/G Mp ratios fr
Page 15 and 16: Previous slides illustrate discrepa
Page 17 and 18: 2/17/2013 Many theoretical models a
Page 19 and 20: Dressed quarks in the Nucleon Dress
Page 21 and 22: Perturbative QCD (pQCD): Asymptotic
Page 23 and 24: GPDs and Electromagnetic FF The fir
Page 25 and 26: The proton is not spherical? Not a
Page 27 and 28: Quark Flavor separation Assume that
Page 29 and 30: Quark Flavor separation (II) In Rob
Page 31 and 32: Fd 1n Fd 2n Fu , 1p Fu , 2p Proto
Page 33 and 34: Each of the neutron Sachs form fact
Page 35 and 36: More about the Rosenbluth versus do
Page 37 and 38: Radiative correction to the last da
Page 39 and 40: Currently 3 attempts to measure two
Page 41 and 42: Preliminary results from run II, No
Page 43 and 44: Two-photon exchange is next term to
Page 45 and 46: P ℓ / P ℓ Born Kivel and Vander
Page 47 and 48: Mainz JLab Mostly Hydrogen Lamb shi
Page 49 and 50: 1) At Jlab E08-007, data taking com
Page 51 and 52: Conclusions continued • Much has
Page 53:
The following collaborators were in
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The Form Factors of the Nucleons: Present Status - Fisica

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