Neutron Charge Form Factor Research Articles

Cross Sections for Coherent Elastic and Inelastic Neutrino-Nucleus Scattering

The prospects of extracting new physics signals in coherent elastic neutrino–nucleus scattering (CEνNS) processes are limited by the precision with which the underlying nuclear structure physics, embedded in the weak nuclear form factor, is known. We present calculations of charge and weak nuclear form factors and CEνNS cross sections on 12C, 16O, 40Ar, 56Fe and 208Pb nuclei. We obtain the proton and neutron densities, and charge and weak form factors by solving Hartree–Fock (HF) equations with a Skyrme (SkE2) nuclear potential. We validate our approach by comparing 208Pb and 40Ar charge form factor predictions with available elastic electron scattering data. Since CEνNS experiments at stopped-pion sources are also well suited to measure inelastic charged–current and neutral–current neutrino–nucleus cross sections, we also present calculations for these processes, incorporating a continuum Random Phase Approximation (CRPA) description on top of the HF–SkE2 picture of the nucleus. Providing both coherent as well as inelastic cross sections in a consistent framework, we aim at obtaining a reliable and detailed comparison of the strength of these processes in the energy region below 100 MeV. Furthermore, we attempt to gauge the level of theoretical uncertainty pertaining to the description of the 40Ar form factor and CEνNS cross sections by comparing relative differences between recent microscopic nuclear theory and widely-used phenomenological form factor predictions. Future precision measurements of CEνNS will potentially help in constraining these nuclear structure details that will in turn improve prospects of extracting new physics.

Covariant spectator theory of np scattering: Deuteron form factors

This paper uses the covariant spectator theory to calculate the deuteron electromagnetic form factors, yielding impressive quantitative results for deuteron observables. Special attention is given to a consistent treatment of currents generated by the nuclear force models obtained from the 2008 high-precision fits to the $N\phantom{\rule{0}{0ex}}N$ scattering data. Noteworthy results are (1) the neutron charge form factor prediction and (2) determination of two off-shell nucleon form factors that contribute to electron-deuteron scattering.

Analysis of excited quark propagator effects on neutron charge form factor

The charge form factor and charge radius of neutron are investigated in the perturbative chiral quark model (PCQM) with considering both the ground and excited states in the quark propagator. A Cornell-like potential is extracted in accordance with the predetermined ground state quark wavefunction, and the excited quark states are derived by solving the Dirac equation with the extracted PCQM potential numerically. The study reveals that the contributions of the excited quark states are considerably influential in the charge form factor and charge radius of neutron as expected, and the total results are significantly improved and increased by nearly four times by including the excited states in the quark propagator. The theoretical PCQM results are found, including the ground and excited quark propagators, in good agreement with the recent lattice QCD values at pion mass of about 130 MeV.

Extraction of the neutron electric form factor from measurements of inclusive double spin asymmetries

Background: Measurements of the neutron charge form factor, GEn, are challenging because the neutron has no net charge. In addition, measurements of the neutron form factors must use nuclear targets which require accurately accounting for nuclear effects. Extracting GEn with different targets and techniques provides an important test of our handling of these effects. Purpose: The goal of the measurement was to use an inclusive asymmetry measurement technique to extract the neutron charge form factor at a four-momentum transfer of 1(GeV/c)2. This technique has very different systematic uncertainties than traditional exclusive measurements and thus serves as an independent check of whether nuclear effects have been taken into account correctly. Method: The inclusive quasielastic reaction 3He⃗(e⃗,e′) was measured at Jefferson Laboratory. The neutron electric form factor, GEn, was extracted at Q2=0.98(GeV/c)2 from ratios of electron-polarization asymmetries measured for two orthogonal target spin orientations. This Q2 is high enough that the sensitivity to GEn is not overwhelmed by the neutron magnetic contribution, and yet low enough that explicit neutron detection is not required to suppress pion production. Results: The neutron electric form factor, GEn, was determined to be 0.0414±0.0077(stat)±0.0022(syst), providing the first high-precision inclusive extraction of the neutron's charge form factor. Conclusions: The use of the inclusive quasielastic 3He⃗(e⃗,e′) with a four-momentum transfer near 1(GeV/c)2 has been used to provide a unique measurement of GEn. This new result provides a systematically independent validation of the exclusive extraction technique results and implies that the nuclear corrections are understood. This is contrary to the proton form factor where asymmetry and differential cross section measurements have been shown to have large systematic differences.Received 24 June 2017DOI:https://doi.org/10.1103/PhysRevC.96.065206©2017 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasPhotonuclear reactionsPhysical SystemsNeutronsPropertiesForm factorsNuclear PhysicsParticles & Fields

Excited nucleon electromagnetic form factors from broken spin-flavor symmetry

A group theoretical derivation of a relation between the N → Δ A charge quadrupole transition and neutron charge form factors is presented.

Charge Form Factor of the Neutron at Low Momentum Transfer from theH→2(e→,e′n)H1Reaction

We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio GEn/GMn was extracted from the beam-target vector asymmetry AedV at four-momentum transfers Q2=0.14, 0.20, 0.29, and 0.42 (GeV/c)2.Received 26 March 2008DOI:https://doi.org/10.1103/PhysRevLett.101.042501©2008 American Physical Society

NEUTRON CHARGE RADIUS: RELATIVISTIC EFFECTS AND THE FOLDY TERM

The neutron charge radius is studied within a light-front model with different spin coupling schemes and wave functions. The cancellation of the contributions from the Foldy term and Dirac form factor to the neutron charge form factor is verified for large nucleon sizes and it is independent of the detailed form of quark spin coupling and wave function. For the physical nucleon our results for the contribution of the Dirac form factor to the neutron radius are insensitive to the form of the wave function while they strongly depend on the quark spin coupling scheme.

The neutron charge form factor and target analyzing powers from [formula omitted] scattering

The charge form factor of the neutron has been determined from asymmetries measured in quasi-elastic 3He(e→,e′n) at a momentum transfer of 0.67 (GeV/c)2. In addition, the target analyzing power, Ayo, has been measured to study effects of final state interactions and meson exchange currents.

Extraction of the neutron charge form factor Gn E(Q2) from the charge form factor of deuteron Gd C(Q2)

We extract the neutron charge form factor from the charge form factor of deuteron obtained from $T_{20}(Q^2)$ data at $0\le Q^2\le$ 1.717 (GeV$^2$). The extraction is based on the relativistic impulse approximation in the instant form of the relativistic Hamiltonian dynamics. Our results (12 new points) are compatible with existing values of the neutron charge form factor of other authors. We propose a fit for the whole set (35 points) taking into account the data for the slope of the form factor at $Q^2 = 0$.

Nucleon charge and magnetization densities from Sachs form factors

Relativistic prescriptions relating Sachs form factors to nucleon charge and magnetization densities are used to fit recent data for both the proton and the neutron. The analysis uses expansions in complete radial bases to minimize model dependence and to estimate the uncertainties in radial densities due to limitation of the range of momentum transfer. We find that the charge distribution for the proton is significantly broad than its magnetization density and that the magnetization density is slightly broader for the neutron than the proton. The neutron charge form factor is consistent with the Galster parametrization over the available range of Q^2, but relativistic inversion produces a softer radial density. Discrete ambiguities in the inversion method are analyzed in detail. The method of Mitra and Kumari ensures compatibility with pQCD and is most useful for extrapolating form factors to large Q^2.

Neutron charge form factor at largeq2

The neutron charge form factor ${G}_{\mathrm{En}}(q)$ is determined from an analysis of the deuteron quadrupole form factor ${F}_{C2}(q)$ data. Recent calculations, based on a variety of different model interactions and currents, indicate that the contributions associated with the uncertain two-body operators of shorter range are relatively small for ${F}_{C2}(q),$ even at large momentum transfer q. Hence, ${G}_{\mathrm{En}}(q)$ can be extracted from ${F}_{C2}(q)$ at large ${q}^{2}$ without undue systematic uncertainties from theory.

Relativistic quark spin coupling effects in the correlations between nucleon electroweak properties

We investigate the effect of different relativistic spin couplings of constituent quarks on nucleon electroweak properties. Within each quark spin coupling scheme the correlations between static electroweak observables are found to be independent of the particular shape of the momentum part of the nucleon light-front wave function. The neutron charge form factor is very sensitive to different choices of spin coupling schemes once the magnetic moment is fitted to the experimental value. However, it is found rather insensitive to the details of the momentum part of the three-quark wave function model.

Moments of the neutron charge form factor and the N --> Delta quadrupole transition.

Recent data allow a new parametrization of the neutron charge form factor GnE. A parameter-free quark-model relation between GnE and the N-->Delta quadrupole form factor G(N-->Delta)C2 is used to predict G(N-->Delta)C2 from GnE data. In particular, <r2n> is related to N-->Delta quadrupole moment Q(N-->Delta), while <r4n> connects to the N-->Delta quadrupole transition radius <r2(N-->Delta)>. From the latter we derive an experimental value for the charge radius of the light constituent quarks r(gamma(q)) = 0.8 fm. Finally, the C2/M1 ratio in pion electroproduction is predicted from the elastic neutron form factor data.

Relations between electromagnetic form factors of baryons

The inclusion of two-body exchange currents in the constituent quark model leads to new relations between the electromagnetic properties of octet and decuplet baryons. In particular, the N → Δ quadrupole transition form factor can be expressed in terms of the neutron charge form factor.

Relativistic quark spin coupling effects in the nucleon electromagnetic form factors

We investigate the effect of different forms of relativistic spin coupling of constituent quarks in the nucleon electromagnetic form factors. The four-dimensional integrations in the two-loop Feynman diagram are reduced to the null-plane, such that the light-front wave function is introduced in the computation of the form factors. The neutron charge form factor is very sensitive to different choices of spin coupling schemes, once its magnetic moment is fitted to the experimental value. The scalar coupling between two quarks is preferred by the neutron data, when a reasonable fit of the proton magnetic momentum is found.

Relativistic effects on the neutron charge form factor in the constituent quark model

The neutron charge form factor G E n ( Q 2) is investigated within a constituent quark model formulated on the light-front. It is shown that, if the quark initial motion is neglected in the Melosh rotations, the Dirac neutron form factor F 1 n ( Q 2) receives a relativistic correction which cancels exactly against the Foldy term in G E n ( Q 2), as it has been recently argued by Isgur. Moreover, at the same level of approximation the ratio of the proton to neutron magnetic form factors G M p ( Q 2)/ G M n ( Q 2) is still given by the naive SU(6)-symmetry expectation, −3/2. However, it is also shown that the full Melosh rotations break SU(6) symmetry, giving rise to G E n ( Q 2)≠0 and G M p ( Q 2)/ G M n ( Q 2)≠−3/2 even when a SU(6)-symmetric canonical wave function is assumed. It turns out that relativistic effects alone cannot explain simultaneously the experimental data on G E n ( Q 2) and G M p ( Q 2)/ G M n ( Q 2).

Nucleon form factors in a relativistic quark model

Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a difference between the relativistic and the nonrelativistic treatments.

The neutron charge form factor in helium-3

In order to measure the charge form factor of the neutron, G n E ( Q 2), one needs to use a neutron bound in a nuclear target. We calculate the change in the form factor for a neutron bound in 3 He, with respect to the free case, using several versions of the quark meson coupling model. It is found that the form factor may be suppressed by as much as 12% at Q 2=0.5 GeV 2 with respect to that of the free neutron.

The A(q 2) deuteron structure function: the contribution of exchange currents associated with the ΔΔ component and the neutron charge form factor

In the present work, contributions to the deuteron electromagnetic structure due to exchange currents involving the ΔΔ component are studied. For a 0.88% probability of this component, it is found that a substantially important contribution to the deuteron charge form factor is obtained. It comes just second in order of importance after that of the pion-pair current. This ΔΔ contribution has its origin in the usual pair current, but at the quark level. Taking into account this new contribution implies a modification of the neutron charge form factor, G E n (q 2), which has been derived from the measurement of the structure function, A(q 2). An interesting observation is made about the derivation of this form factor. This calls for an extension of the accurate determination of A(q 2) to higher values of q 2.

Polarized 3He and neutron form factors

The transverse-longitudinal response function R TL′ of 3He is studied with full inclusion of final state interaction. Contributions from each nucleon form factor are calculated. Possible relativistic effect is examined in extracting neutron charge form factor from associated spin-dependent asymmetry in inclusive scattering of polarized electrons from polarized 3He.