Electromagnetic Structure Of Nucleon Research Articles

PROBING THE ELECTROMAGNETIC STRUCTURE OF NUCLEONS

PROBING THE ELECTROMAGNETIC STRUCTURE OF NUCLEONS

On a Description of the Nucleon Electromagnetic Structure by Effective Proton and Neutron form Factors

On a Description of the Nucleon Electromagnetic Structure by Effective Proton and Neutron form Factors

An experimental program with high duty-cycle polarized and unpolarized positron beams at Jefferson Lab

Positron beams, both polarized and unpolarized, are identified as essential ingredients for the experimental programs at the next generation of lepton accelerators. In the context of the hadronic physics program at Jefferson Lab (JLab), positron beams are complementary, even essential, tools for a precise understanding of the electromagnetic structure of nucleons and nuclei, in both the elastic and deep-inelastic regimes. For instance, elastic scattering of polarized and unpolarized electrons and positrons from the nucleon enables a model independent determination of its electromagnetic form factors. Also, the deeply-virtual scattering of polarized and unpolarized electrons and positrons allows unambiguous separation of the different contributions to the cross section of the lepto-production of photons and of lepton-pairs, enabling an accurate determination of the nucleons and nuclei generalized parton distributions, and providing an access to the gravitational form factors. Furthermore, positron beams offer the possibility of alternative tests of the Standard Model of particle physics through the search of a dark photon, the precise measurement of electroweak couplings, and the investigation of charged lepton flavor violation. This document discusses the perspectives of an experimental program with high duty-cycle positron beams at JLab.

Proton Electromagnetic Form Factors Data Are in Disagreement with New Electron-Positron Annihilation into Proton-Antiproton Pair Total Cross Section Measurements

In this paper a consistency of new very precise data on electron-positron annihilation into proton-antiproton pair total cross section with existing proton and neutron electromagnetic form factors data is investigated. First, the result is represented by a theoretically predicted dashed line for the total cross section obtained in the simultaneous analysis of the proton and neutron form factors data by the advanced nucleon electromagnetic structure Unitary and Analytic model, and then, as the neutron data are always less precise from objective reasons than the proton data, the result is also represented by a theoretically predicted full line for the total cross section obtained in the analysis of only the proton form factors data in space-like and time-like regions by the advanced proton electromagnetic structure Unitary and Analytic model. In both cases one finds disagreement between the electron-positron annihilation into proton-antiproton pair total cross section data and the corresponding form factors data, which is demonstrated by a disagreement of the dashed and full curves representing theoretically predicted electron-positron annihilation into proton-antiproton pair total cross sections behaviors.

Nucleon Electromagnetic Structure from Lattice QCD

We present an evaluation of nucleon to Δ electromagnetic form factors within Lattice QCD. The EMR and CMR ratios are calculated both in the quenched theory and using two degenerate flavors of dynamical Wilson fermions. We obtain values in qualitative agreement to experiment. In addition, we evaluate the isovector Sachs electromagnetic form factors of the nucleon both in the quenched and unquenched theory for momentum transfer squared in the range between 0.1 and 2 GeV2. The nucleon magnetic moment and r.m.s. radii are obtained using chiral effective theory to extrapolate to the physical pion mass.

Electromagnetic structure of nucleon and Roper in soft-wall AdS/QCD

We present an improved study of the electromagnetic form factors of the nucleon and of the Roper-nucleon transition using an extended version of the effective action of soft-wall AdS/QCD. We include novel contribution from additional nonminimal terms, which do not renormalize the charge and do not change the normalization of the corresponding form factors, but the inclusion of these terms results in an important contribution to the momentum dependence of the form factors and helicity amplitudes.

Numerical values of thefF,fD, andfScoupling constants in the SU(3) invariant interaction Lagrangian of the vector-meson nonet with1/2+octet baryons

It is demonstrated how an utilization of all existing experimental information on electric and magnetic nucleon form factors, to be described by the Unitary and Analytic (U\&A) nucleon electromagnetic structure model in space-like and time-like regions simultaneously, can provide numerical values of $f^F$, $f^D$, $f^S$ coupling constants in $SU(3)$ invariant interaction Lagrangian of the vector-meson nonet with $1/2^+$ octet baryons. The latter, together with universal vector-meson coupling constants $f_V$, play an essential role in a prediction of $1/2^+$ octet hyperon electromagnetic form factors behaviors.

Experimental progress and status on nucleon electromagnetic form factors

Nucleon electromagnetic form factors are the fundamental quantities that are related to a two-dimensional view of the charge and magnetization distribution in the nucleon. They are essential in understanding the nucleon electromagnetic structure. In this article, we briefly summarize the recent experimental progress on this topic, and introduce several experiments related to the nucleon electromagnetic form factors in the near future.

Quark–hadron duality constraints on γZ box corrections to parity-violating elastic scattering

We examine the interference γZ box corrections to parity-violating elastic electron–proton scattering in the light of the recent observation of quark–hadron duality in parity-violating deep-inelastic scattering from the deuteron, and the approximate isospin independence of duality in the electromagnetic nucleon structure functions down to Q2≈1 GeV2. Assuming that a similar behavior also holds for the γZ proton structure functions, we find that duality constrains the γZ box correction to the proton's weak charge to be ℜe□γZV=(5.4±0.4)×10−3 at the kinematics of the Qweak experiment. Within the same model we also provide estimates of the γZ corrections for future parity-violating experiments, such as MOLLER at Jefferson Lab and MESA at Mainz.

Nuclear medium effects in structure functions of nucleon at moderate [formula omitted

Recent experiments performed on inclusive electron scattering from nuclear targets have measured the nucleon electromagnetic structure functions F1(x,Q2), F2(x,Q2) and FL(x,Q2) in 12C, 27Al, 56Fe and 64Cu nuclei. The measurements have been done in the energy region of 1 GeV2<W2<4 GeV2 and Q2 region of 0.5 GeV2<Q2<4.5 GeV2. We have calculated nuclear medium effects in these structure functions arising due to the Fermi motion, binding energy, nucleon correlations, mesonic contributions from pion and rho mesons and shadowing effects. The calculations are performed in a local density approximation using a relativistic nucleon spectral function which includes nucleon correlations. The numerical results are compared with the recent experimental data from JLab and also with some earlier experiments.

Nucleon form factors for elastic electron-deuteron scattering at high momentum transfer

Elastic electron-deuteron scattering at high momentum transfer is investigated within the Bethe-Salpeter approach. The relativistic covariant Graz II separable kernel of nucleon-nucleon interactions is used to analyze the deuteron structure functions, form factors, and tensor of polarization components. The modern data for the electromagnetic structure of nucleons from the double polarization experiments, as well as some other models of the nucleon form factors, are considered.

Advanced nucleon electromagnetic structure model and charge proton rms radius

Description of the nucleon electromagnetic structure by advanced Unitary and Analytic approach, respecting SU(3) symmetry and analyzing also the recent Mainz MAMI data with impact on the proton charge radius to be compared with the results from the muon hydrogen atom spectroscopy.

The advanced nucleon electromagnetic structure model and prediction of hyperon electromagnetic form factors

The advanced Unitary and Analytic model of electromagnetic structure of nucleons is applied for sophisticated prediction of hyperon electromagnetic form factors in space-like and time-like regions simultaneously. The static parameters of hyperons are predicted and compared with chiral perturbation theory calculations.

Vector and tensor polarizations in [formula omitted] by advanced nucleon electromagnetic structure model

Recently an advanced nucleon electromagnetic structure model has been developed and in this paper predictions of vector and tensor polarizations in e+e−→pp¯ process by this model are presented.

Photonuclear interactions at very high energies and vector meson dominance

We show that nucleon electromagnetic structure functions of deep inelastic scattering in Regge-Gribov limit (fixed Q-squared, asymptotically large 1/x and s) can be well described in the two-component (soft + hard) approach. In the concrete model elaborated by authors, the soft part of the virtual photon-nucleon scattering is given by the vector meson dominance, with taking into account the radial excitations of the rho-meson and nondiagonal transitions in meson-nucleon interactions. The hard part is calculated by using the dipole factorization, i.e., the process is considered as the dissociation of the photon into a -pair (the "color dipole") and the subsequent interaction of this dipole with the nucleon. The dipole cross section has a Regge-type s-dependence and vanishes in the limit of large transverse sizes of the dipole. We give the brief description of the model and present results of the detailed comparison of model predictions with experimental data for electromagnetic structure functions of the nucleon.

New value of the proton charge root mean square radius

The non-dipole behavior of GEp(Q2) in the space-like region with the zero around Q2=13GeV2 is found in a global analysis of all existing nucleon electromagnetic form factor data by means of a sophisticated analytic model of nucleon electromagnetic structure. From such behavior of GEp(Q2), the charge proton root mean square (rms) radius is compatible with the value obtained recently from spectroscopy of the muon hydrogen atom.

Implications of the new proton charge rms radius from spectroscopy of muon hydrogen atom

It is demonstrated a coincidence of the proton electric rms radius from the global analysis of the JLab proton polarization data together with all other existing nucleon electromagnetic form factor data in the framework of the Unitary & Analytic model of nucleon electromagnetic structure with its value recently determined in a spectroscopy of muon hydrogen atom.The result confirms a non-dipole behavior of the proton electric form factor in the space-like region and strengthen a belief in an existence of the proton electric form factor zero revealed in global analysis of nucleon form factors data.

Electromagnetic properties of hyperons

In the framework of unitary and analytic model of nucleon electromagnetic structure, the values of nucleon coupling constants are received from the fit of nucleon data. With the help of SU(3) relations the coupling constants of other hyperons, i.e., Λ, Σ + , Σ 0 , Σ − , Ξ 0 , Ξ − are calculated. The values of hyperon coupling constants are used to predict the behaviour of hyperon electromagnetic form factors and corresponding cross sections e + e − → hyperon–antihyperon.

A two component model describing nucleon structure functions in the low-x region

A two component model describing the electromagnetic nucleon structure functions in the low-x region, based on generalized vector dominance and color dipole approaches is briefly described. The model operates with the mesons of ρ -family having the mass spectrum of the form m n 2 = m ρ 2 ( 1 + 2 n ) and takes into account the nondiagonal transitions in meson-nucleon scattering. The special cut-off factors are introduced in the model, to exclude the γ − q q ¯ − V transitions in the case of narrow q q ¯ -pairs. For the color dipole part of the model the well known FKS-parameterization is used.

Phenomenological insight into the space-like proton elastic form factor using the deuteron impulse approximation

The analysis of the JLab proton polarization data on the ratio {mu}{sub p}G{sub Ep}(t)/G{sub Mp}(t) in the framework of the unitary and analytic model of nucleon electromagnetic structure implicates surprising nondipole behavior of the proton electric form factor G{sub Ep}(t) in the space-like region with the zero around the momentum transfer squared value t=-Q{sup 2}=-13 GeV{sup 2}. This result differs from the unpolarized cross-section measurements giving the dipole behavior of G{sub Ep}(t) by means of the Rosenbluth technique. Recent investigations demonstrate that inclusion of a two-photon mechanism could solve the problem, which plays an important role for the unpolarized cross section, but it is negligible for the polarization ratio. Here, investigating a size of a difference in a prediction of the deuteron elastic structure functions A(t),B(t) by both, the nondipole and the old dipole, behaviors of G{sub Ep}(t) in space-like region through the nonrelativistic impulse approximation, we have come to the conclusion that the two-photon mechanism plays much less of a role for the unpolarized electron-deuteron elastic scattering than for the unpolarized electron-proton elastic scattering.