Pauli Radius of the Proton

Using a procedure based on interpolation via continued fractions supplemented by statistical sampling, we analyze proton magnetic form factor data obtained via electron+proton scattering on Q 2 ∈ [0.027, 0.55] GeV2 with the goal of determining the proton magnetic radius. The approach avoids assumptions about the function form used for data interpolation and ensuing extrapolation onto Q 2 ≃ 0 for extraction of the form factor slope. In this way, we find r M = 0.817(27) fm. Regarding the difference between proton electric and magnetic radii calculated in this way, extant data are seen to be compatible with the possibility that the slopes of the proton Dirac and Pauli form factors, F 1,2(Q 2), are not truly independent observables; to wit, the difference F ′ 1 ( 0 ) − F ′ 2 ( 0 ) / κ p = [ 1 + κ p ] / [ 4 m p 2 ] , viz., the proton Foldy term.

Tau $$g{-}2$$ at $$e^-e^+$$ colliders with momentum-dependent form factor

The deviation between the prediction based on the standard model and the measurement of the muon $$g{-}2$$ g - 2 is currently at $$3{-}4 \sigma $$ 3 - 4 σ . If this discrepancy is attributable to new physics, it is expected that the new contributions to the tau $$g{-}2$$ g - 2 even larger than those of muon due to its large mass. However, it is much more difficult to directly measure the tau $$g{-}2$$ g - 2 because of its short lifetime. In this report, we consider the effect of the tau $$g{-}2$$ g - 2 at $$e^-e^+$$ e - e + colliders using a model independent approach. Using the tau pair production channel at the Large Electron Position Collider (LEP), we have determined the allowed range for the new physics contribution of the tau $$g{-}2$$ g - 2 assuming a q-square-dependence ansatz for the magnetic form factor. We also investigated the prospect at future $$e^+e^-$$ e + e - colliders, such as International Linear Collider, the Compact Linear Collider, the Future Circular $$e^+e^-$$ e + e - Collider, and Circular Electron Positron Collider, and determined the expected allowed range for the new physics contribution to the tau anomalous magnetic moment. The best limits are about $$4{-}5$$ 4 - 5 times more severe than the LEP one due to the beam polarization and the high luminosities at future colliders.

Magnetic Scattering: General Properties

The basic theory of magnetic scattering is presented. A response function for magnetic scattering is defined, and expressed in terms partial response functions. The relation between the partial response functions and the correlation function for components of the magnetization is obtained, and the dynamical part of the partial reponse functions is linked via the fluctuation-dissipation theorem to the absorptive part of the generalized susceptibility. It is shown how the dipole approximation can be used to simply the magnetic scattering operator for localized electrons, and the magnetic form factor is introduced. Examples of the use of the dipole magnetic form factor, as well as more general anisotropic magnetic form factors, are given. A comparison with the X-ray atomic form factor is given. Various sum rules for the magnetic response function and generalized susceptibility are obtained.

Sensitivity of elastic electron scattering off the 3He to the nucleon form factors

Elastic electron-3He scattering is studied in the relativistic impulse approximation. The amplitudes for the three-nucleon system – 3He – are obtained by solving the relativistic generalization of the Faddeev equation. The charge and magnetic form factor are calculated and compared with the experimental data for the momentum transfer squared up to 100 fm-2. The influence of the various nucleon form factors is investigated.

The electromagnetic form factors of Λ hyperon in e+e−→Λ̄Λ

We study the electromagnetic form factors of [Formula: see text] hyperon in the time-like region using the experimental data in the exclusive production of [Formula: see text] pair in electron–positron annihilation. We present a pQCD inspired parametrization of [Formula: see text] and [Formula: see text] with only two parameters, and we consider a suppression mechanism of the electric form factor [Formula: see text] compared to the magnetic form factor [Formula: see text]. The parameters are determined through fitting our parametrization to the data of the effective form factor [Formula: see text] from the DM2, BaBar and BESIII Collaborations in the reaction [Formula: see text]. We use the parametrizations for [Formula: see text] and [Formula: see text] to calculate the Born cross-sections as well as the ratio [Formula: see text]. Except the threshold region, our parametrization can describe the known behavior of the existing data of effective form factor, Born cross-section and the ratio [Formula: see text] from the BaBar, DM2 and BESIII Collaborations. We also predict the double spin polarization observables [Formula: see text], [Formula: see text] and [Formula: see text] in [Formula: see text] which could provide more information on the size of the lambda EMFFs as well as their phase angles.