Empirical parametrization of the two-photon-exchange effect contributions to the electron-proton elastic scattering cross section

I. A. Qattan, A. Alsaad

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Abstract

The most recent electron-proton elastic scattering data were re-analyzed using an empirical parametrization of the two-photon-exchange (TPE) effect contributions to σR. The TPE effect contribution F(Q2) was double Taylor series expanded as a polynomial of order n keeping only terms linear in to account for the experimentally observed and verified linearity of the Rosenbluth plots. We fix the ratio R=GEp/GMp to be that obtained from a fit to the recoil-polarization data and parametrize σR first by a three-parameter formula (fit I) and then by a two-parameter formula (fit III). In contrast to previous analyses, the fit parameter GMp2 as obtained from these fits is either smaller or equal to the values obtained from our conventional Rosenbluth fit (fit II) but never larger. The ratio g(Q2)/GMp2 which represents the ratio of the TPE and one-photon-exchange (OPE) effect contributions to the intercept of σR is large and it ranges 3%-88%. The ratio R 1γ-2γ=τf(Q2)/GEp2 which represents the ratio of the TPE and OPE effect contributions to the slope of σR is also large, reaching a value of 12.0-14.4 at Q2= 5.25 (GeV/c)2. The ratio R 1γ-2γ as obtained from fits I and III is consistent, within error, with those obtained from previous analyses. Our formulas seem to explain the linearity of σR. Moreover, our analysis shows that the extracted GEp2 and GMp2 using the conventional Rosenbluth separation method can in fact be broken into the usual OPE and TPE contributions. Therefore, σR can in fact be derived under weaker conditions than those imposed by the Born approximation. Our results show that the TPE amplitudes, g(Q2)/GMp2 and f(Q2)/GMp2, are sizable and grow with Q2 value up to Q2~ 6 (GeV/c)2 in agreement with previous studies. A revision of and comparison to previous analyses are also presented.

Original languageBritish English
Article number054307
JournalPhysical Review C - Nuclear Physics
Volume83
Issue number5
DOIs
StatePublished - 12 May 2011

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