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      Constraints on the Nucleon Strange Form Factors at Q^2 ~ 0.1 GeV^2

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          Abstract

          We report the most precise measurement to date of a parity-violating asymmetry in elastic electron-proton scattering. The measurement was carried out with a beam energy of 3.03 GeV and a scattering angle <theta_lab>=6 degrees, with the result A_PV = -1.14 +/- 0.24 (stat) +/- 0.06 (syst) parts per million. From this we extract, at Q^2 = 0.099 GeV^2, the strange form factor combination G_E^s + 0.080 G_M^s = 0.030 +/- 0.025 (stat) +/- 0.006 (syst) +/- 0.012 (FF) where the first two errors are experimental and the last error is due to the uncertainty in the neutron electromagnetic form factor. This result significantly improves current knowledge of G_E^s and G_M^s at Q^2 ~0.1 GeV^2. A consistent picture emerges when several measurements at about the same Q^2 value are combined: G_E^s is consistent with zero while G_M^s prefers positive values though G_E^s=G_M^s=0 is compatible with the data at 95% C.L.

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          A Coherent Interpretation of the Form Factors of the Nucleon in Terms of a Pion Cloud and Constituent Quarks

          The recent unbiased measurements of the electric form factor of the neutron suggest that its shape may be interpreted as a smooth broad distribution with a bump at Q^2 \approx 0.3(GeV/c)^2 superimposed. As a consequence the corresponding charge distribution in the Breit frame shows a negative charge extending as far out as 2fm. It is natural to identify this charge with the pion cloud. This realisation is then used to reanalyse all old and new data of the electric and magnetic from factors of the proton and the neutron by a phenomenological fit and by a fit based on the constituent quark model. It is shown that it is possible to fit all form factors coherently with both ansaetzen and that they all show the signal of the pion cloud.
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            Strange nucleon form factors in the perturbative chiral quark model

            We apply the perturbative chiral quark model at one loop to calculate the strange form factors of the nucleon. A detailed numerical analysis of the strange magnetic moments and radii of the nucleon, and also the momentum dependence of the form factors is presented.
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              Radiative Corrections to Elastic Electron-Proton Scattering for Polarized Electrons

              We analyze the radiative correction to high energy elastic electron-proton scattering of polarized electrons. We show that if the approximations inherent in the calculations developed by Tsai and given in the work of Mo and Tsai, which have been used in the analysis of almost all experimental data pertaining to medium and high energy elastic electron scattering for the past three decades, are maintained, then the same radiative correction applies both in the case of initially polarized and unpolarized electrons.
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                Author and article information

                Journal
                07 June 2005
                2005-12-23
                Article
                10.1016/j.physletb.2006.03.011
                nucl-ex/0506011
                b8c23723-b5d1-42f4-8f21-3b1bb1240423
                History
                Custom metadata
                Phys.Lett.B635:275-279,2006
                minor wording changes for clarity, updated references, dropped one figure to improve focus
                nucl-ex

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