The Form Factors of the Nucleons: Present Status - Fisica

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Conclusions It has been 13+ years since the first recoil polarization measurement above 0.5 GeV 2 of G Ep/G Mp was completed. Nothing great had been expected, and the results were only suggestive of something new. Initial approval was to 3 GeV 2 , granted 3.5 GeV 2 by Larry Cardman during the experiment. Fig. 18 in Punjabi et al, Phys. Rev. C71, 055202 (2005); (revised from M.K. Jones et al. PRL 84, 1398 (2000)). Please note size of both statistical and systematic uncertainties. 2/17/2013 C.F. Perdrisat SAEMP Trento 2013 50
Conclusions continued • Much has happened since the results of the first double-polarization ep Form Factor experiment at Jlab (GEp(I)); the results of GEp(II) and GEp(III) have challenged half a century of cross section measurements! •Theorists have suggested that two photon exchange might explain the difference, between Rosenbluth and polarization, demonstrating that polarization experiments give ~ the correct results (with per percent level 2-photon correction). •The neutron is slowly revealing its electric structure, with tantalizing possibilities, which need to be verified; does G En cross zero near 10 GeV 2 ? •Now new challenge: why is the proton radius from μ-onic hydrogen Lamb shift smaller than that from hydrogen Lamb shift and elastic ep? •On the theoretical front, all older models were revised in the last 10 years, and new ones developed; getting closer to QCD. 2/17/2013 C.F. Perdrisat SAEMP Trento 2013 51
Page 1 and 2: The Form Factors of the Nucleons: P
Page 3 and 4: Results for the proton’s G Ep and
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: 1) At Jlab E08-007, data taking com
Page 53: The following collaborators were in

The Form Factors of the Nucleons: Present Status - Fisica

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