Magnetic Form Factor Research Articles

EFFECTS OF SCALAR BOSON IN ELASTIC PROTON-ELECTRON SCATTERING

The differential cross section for the elastic scattering of unpolarized protons on unpolarized electrons at rest is calculated taking into account two mechanisms: one-photon and scalar-boson exchange. The spin correlation coefficients, when the proton beam and the electron target are both arbitrarily polarized, have also been calculated. These observables are calculated in terms of the proton electromagnetic form factors, namely magnetic and electric ones. Some peculiarities of the inverse kinematics (the mass of the colliding particle is larger than mass of the target particle) have been discussed. It was shown that all the spin correlation coefficients in the elastic proton electron collisions are proportional to the proton magnetic form factor. The same behaviour takes place for the spin correlation coefficients in the elastic electron proton scattering (the electron beam and proton target are both polarized). It was shown that only the interference of the two mechanisms (one-photon and one-boson) gives nonzero contribution to the spin correlation coefficients. If the spin vectors of the proton beam and electron target lie in the reaction plane then the corresponding spin correlation coefficients are zero for the case when scattered electron momentum is in the direction of the proton beam momentum.

Nucleon Axial and Electromagnetic Form Factors

We present results for the isovector axial, induced pseudoscalar, electric, and magnetic form factors of the nucleon. The calculations were done using 2 + 1 + 1-flavor HISQ ensembles generated by the MILC collaboration with lattice spacings a ≈ 0.12, 0.09, 0.06 fm and pion masses Mπ ≈ 310, 220, 130 MeV. Excited-states contamination is controlled by using four-state fits to two-point correlators and by comparing two-versus three-states in three-point correlators. The Q2 behavior is analyzed using the model independent z-expansion and the dipole ansatz. Final results for the charge radii and magnetic moment are obtained using a simultaneous fit in Mπ, lattice spacing a and finite volume.

Structure of the Nucleon and its Excitations

The structure of the ground state nucleon and its finite-volume excitations are examined from three different perspectives. Using new techniques to extract the relativistic components of the nucleon wave function, the node structure of both the upper and lower components of the nucleon wave function are illustrated. A non-trivial role for gluonic components is manifest. In the second approach, the parity-expanded variational analysis (PEVA) technique is utilised to isolate states at finite momenta, enabling a novel examination of the electric and magnetic form factors of nucleon excitations. Here the magnetic form factors of low-lying odd-parity nucleons are particularly interesting. Finally, the structure of the nucleon spectrum is examined in a Hamiltonian effective field theory analysis incorporating recent lattice-QCD determinations of low-lying two-particle scattering-state energies in the finite volume. The Roper resonance of Nature is observed to originate from multi-particle coupled-channel interactions while the first radial excitation of the nucleon sits much higher at approximately 1.9 GeV.

Study of the in-medium nucleon electromagnetic form factors using a light-front nucleon wave function combined with the quark-meson coupling model

We study the nucleon electromagnetic (EM) form factors in symmetric nuclear matter as well as in vacuum within a light-front approach using the in-medium inputs calculated by the quark-meson coupling model. The same in-medium quark properties are used as those used for the study of in-medium pion properties. The zero of the proton EM form factor ratio in vacuum, the electric to magnetic form factor ratio μpGEp(Q2)/GMp(Q2) (Q2=−q2>0 with q being the four-momentum transfer), is determined including the latest experimental data by implementing a hard constituent quark component in the nucleon wave function. A reasonable fit is achieved for the ratio μpGEp(Q2)/GMp(Q2) in vacuum, and we predict that the Q02 value to cross the zero of the ratio to be about 15 GeV2. In addition the double ratio data of the proton EM form factors in 4He and H nuclei, [GEp4He(Q2)/G4HeMp(Q2)]/[GEp1H(Q2)/GMp1H(Q2)], extracted by the polarized (e→,e′p→) scattering experiment on 4He at JLab, are well described. We also predict that the Q02 value satisfying μpGEp(Q02)/GMp(Q02)=0 in symmetric nuclear matter, shifts to a smaller value as increasing nuclear matter density, which reflects the facts that the faster falloff of GEp(Q2) as increasing Q2 and the increase of the proton mean-square charge radius. Furthermore, we calculate the neutron EM form factor double ratio in symmetric nuclear matter for 0.1<Q2<1.0 GeV2. The result shows that the neutron double ratio is enhanced relative to that in vacuum, while for the proton it is quenched, and agrees with an existing theoretical prediction.

Muon anomalous magnetic moment in the standard model extension

We consider the standard model extension to explore the anomalous magnetic dipole moment of the muon. In the QED part of the theory for the CP and CPT-even Lorentz parameter $c_{\mu\nu}$, all independent electromagnetic form factors depend on a new scalar as $p'.c.p$. Therefore, the form factors, even in zero momentum transfer, can be energy dependent. We examine the magnetic form factor to find such an energy dependent up to the one loop level at the leading order of $c_{\mu\nu}$. We show that at the high energy limit (but low enough to satisfy $p^2/m^2\ll1$) there is an enhancement on the muon anomalous magnetic moment. For the first time, we find a bound on the $c_{\mu\nu}$ components for the muon as $[c_{TT}+0.35(c_{XX}+c_{YY})+0.28c_{ZZ}]$, which is about $10^{-11}$ in a terrestrial experiment

Transverse Magnetic Electron Scattering Form Factors for Some Odd-A Nuclei Using Shell Model and Hartree–Fock Calculations

Shell model and Hartree–Fock (HF) calculations have been adopted to study the nuclear structure for some odd-A nuclei; 17O, 27Al, 39K, and 51V. The single-particle nuclear density distributions, the associated nuclear radii, and the transverse magnetic form factors were investigated. The wave functions have been utilized from the shell model using USDA and SAS two-body effective interactions for these nuclei with the sd and d3f7 shell model spaces. On the other hand, different Skyrme parameterizations have been used within the HF method to get the single-particle potential which is used to calculate the single-particle matrix elements. The calculated form factors have been compared with available experimental data.

Sea quarks contribution to the nucleon magnetic moment and charge radius at the physical point

We report a comprehensive analysis of the light and strange disconnected-sea quarks contribution to the nucleon magnetic moment, charge radius, and the electric and magnetic form factors. The lattice QCD calculation includes ensembles across several lattice volumes and lattice spacings with one of the ensembles at the physical pion mass. We adopt a model-independent extrapolation of the nucleon magnetic moment and the charge radius. We have performed a simultaneous chiral, infinite volume, and continuum extrapolation in a global fit to calculate results in the continuum limit. We find that the combined light and strange disconnected-sea quarks contribution to the nucleon magnetic moment is ${\ensuremath{\mu}}_{M}(\mathrm{DI})=\ensuremath{-}0.022(11)(09)\text{ }\text{ }{\ensuremath{\mu}}_{N}$ and to the nucleon mean square charge radius is $⟨{r}^{2}{⟩}_{E}(\mathrm{DI})=\ensuremath{-}0.019(05)(05)\text{ }\text{ }{\mathrm{fm}}^{2}$ which is about $1/3$ of the difference between the $⟨{r}_{p}^{2}{⟩}_{E}$ of electron-proton scattering and that of a muonic atom and so cannot be ignored in obtaining the proton charge radius in the lattice QCD calculation. The most important outcome of this lattice QCD calculation is that while the combined light-sea and strange quarks contribution to the nucleon magnetic moment is small at about 1%, a negative 2.5(9)% contribution to the proton mean square charge radius and a relatively larger positive 16.3(6.1)% contribution to the neutron mean square charge radius come from the sea quarks in the nucleon. For the first time, by performing global fits, we also give predictions of the light and strange disconnected-sea quarks contributions to the nucleon electric and magnetic form factors at the physical point and in the continuum and infinite volume limits in the momentum transfer range of $0\ensuremath{\le}{Q}^{2}\ensuremath{\le}0.5\text{ }\text{ }{\mathrm{GeV}}^{2}$.

Dependence of the inverse opal magnetic form-factor on the degree of sintering: Micromagnetic study

Ni- and Co-based inverse opals can be considered as a three-dimensional network of nanoobjects connected with each other by elongated crosspieces (legs). Inverse opals magnetic properties strongly depend on the legs aspect ratio which can be tuned during fabrication process. We study this dependence by means of micromagnetic simulations. We have found the range of ice-rule validity and studied limiting cases of high and low legs aspect ratio. We also investigate the value of the transverse magnetization component which should appear if the external field is applied perpendicular to one of the legs. Legs aspect ratio which corresponds to the maximal value of this component has been found. Finally, we calculate the dependence of the magnetic form factor on the external field for considered models. These results can be directly compared with experiment.

JLab Measurements of the ^{3}He Form Factors at Large Momentum Transfers.

The charge and magnetic form factors, F_{C} and F_{M}, respectively, of ^{3}He are extracted in the kinematic range 25 fm^{-2}≤Q^{2}≤61 fm^{-2} from elastic electron scattering by detecting ^{3}He recoil nuclei and scattered electrons in coincidence with the two High Resolution Spectrometers of the Hall A Facility at Jefferson Lab. The measurements find evidence for the existence of a second diffraction minimum for the magnetic form factor at Q^{2}=49.3 fm^{-2} and for the charge form factor at Q^{2}=62.0 fm^{-2}. Both minima are predicted to exist in the Q^{2} range accessible by this Jefferson Lab experiment. The data are in qualitative agreement with theoretical calculations based on realistic interactions and accurate methods to solve the three-body nuclear problem.

Electromagnetic and gravitational form factors by using the modified Gaussian ansatz for [formula omitted

In this study, the contribution of the u and d quark electromagnetic form factors for the proton and neutron has been studied as well as regaining the nucleon form factors by considering the modified Gaussian ansatz based on GPDs and using an appropriate PDFs in which we consider the minimum parameters in comparison with other proposed parameterizations in calculating form factors. Our obtained results for u and q quark show suitable agreement with experimental data in the range 0 GeV2<−t<4.5 GeV2 of momentum transfer. Additionally, we calculate the N→Δ magnetic transition form factor, the gravitational form factor, and transverse density for quarks of nucleon. Finally, we compare our result with other previous works by considering the advantage of our used parameterization for u and d quark, proton, and neutron.

Magnetic structure in a U(Ru0.92Rh0.08)2Si2 single crystal studied by neutron diffraction in static magnetic fields up to 24 T

We report the high-field induced magnetic phase in single crystal of U(Ru0.92Rh0.08)2Si2. Our neutron study combined with high-field magnetization, shows that the magnetic phase above the first metamagnetic transition at Hc1 = 21.6 T has an uncompensated commensurate antiferromagnetic structure with propagation vector Q2 = ( 2/3 0 0) possessing two single-Q domains. U moments of 1.45 (9) muB directed along the c axis are arranged in an up-up-down sequence propagating along the a axis, in agreement with bulk measurements. The U magnetic form factor at high fields is consistent with both the U3+ and U4+ type. The low field short-range order that emerges from the pure URu2Si2 due to Rh-doping is initially strengthened by the field but disappears in the field-induced phase. The tetragonal symmetry is preserved across the transition but the a axis lattice parameter increases already at low fields. Our results are in agreement with itinerant electron model with 5f states forming bands pinned in the vicinity of the Fermi surface that is significantly reconstructed by the applied magnetic field.

A method for measuring D* electromagnetic form factors in e+ e− annihilation**Supported by National Natural Science Foundation of China (11675166)

We describe a method for measuring the electromagnetic form factors of the D* meson at time-like momentum transfer in e+ e− annihilation. This is to study the joint angular distribution of the e+e−→γ*→D*+D*−, D*+→D0π+, and D*−→D̅0 π− processes. The magnitudes and relative phases of the charge, magnetic and quadrupole form factors can be determined. The method can also be applied to other vector particles.

Charged current quasi elastic scattering of muon neutrino with nuclei

We present a study on the charge current quasi elastic scattering of $\nu_\mu$ from nucleon and nuclei which gives a charged muon in the final state. To describe nuclei, the Fermi Gas model has been used with proposed Pauli suppression factor. The diffuseness parameter of the Fermi distribution has been obtained using experimental data. We also investigate different parametrizations for electric and magnetic Sach's form factors of nucleons. Calculations have been made for CCQES total and differential cross sections for the cases of $\nu_{\mu}-N$, $\nu_{\mu}-^{12}C$ and $\nu_{\mu}-^{56}Fe$ scatterings and are compared with the data for different values of the axial mass. The present model gives excellent description of measured differential cross section for all the systems.

Pr-magnetism in the quasi-skutterudite compound PrFe2Al8

The intermetallic compound PrFe2Al8 that possesses a three-dimensional network structure of Al polyhedra centered at the transition metal element Fe and the rare earth Pr is investigated through neutron powder diffraction and inelastic neutron scattering in order to elucidate the magnetic ground state of Pr and Fe and the crystal field effects of Pr. Our neutron diffraction study confirms long-range magnetic order of Pr below K in this compound. Subsequent magnetic structure estimation reveals a magnetic propagation vector with a magnetic moment value of /Pr along the orthorhombic c-axis and evidence the lack of ordering in the Fe sublattice. The inelastic neutron scattering study reveals one crystalline electric field excitation near 19 meV at 5 K in PrFe2Al8. The energy-integrated intensity of the 19 meV excitation as a function of follows the square of the magnetic form factor of thereby confirming that the inelastic excitation belongs to the Pr sublattice. The second sum rule applied to the dynamic structure factor indicates only 1.6(2) evolving at the 19 meV peak compared to the 3.58 for free , indicating that the crystal field ground state is magnetic and the missing moment is associated with the resolution limited quasi-elastic line. The magnetic order occurring in Pr in PrFe2Al8 is counter-intuitive to the symmetry-allowed crystal field level scheme, hence, is suggestive of exchange-mediated mechanisms of ordering stemming from the magnetic ground state of the crystal field levels.

Formula omitted] transition in lattice QCD

We evaluate the electromagnetic Ξcγ→Ξc′ transition on 2+1 flavor lattices corresponding to a pion mass of ∼156 MeV. We extract the magnetic Sachs and Pauli form factors which give the Ξc–Ξc′ transition magnetic moment and the decay widths of Ξc′ baryons. We did not find a signal for the magnetic form factor of the neutral transition Ξc0γ→Ξc′0, which is suppressed by the U-spin flavor symmetry. As a byproduct, we extract the magnetic form factors and the magnetic moments of Ξc and Ξc′ baryons, which give an insight to the dynamics of u/d, s and c quarks having masses at different scales.

New POLDI – project of reincarnation of a polarized neutron diffractometer at the reactor PIK

The project of a considerable modernization of the polarized neutron diffractometer POLDI is discussed. It assumes the adoption of POLDI to a broader range of magnetic investigations such as determination of magnetic structures, detailed investigation of complex magnetic structures, studies of magnetic domains, study of the magnetization density maps, magnetic form-factor particularities, local susceptibility, etc. The flexible construction should permit to use either spherical neutron polarimetry technique or flipping ratio technique. Different types of polarization system were analyzed. Original focusing fan-like bender is proposed as polarizer unit. Our simulations give evidence that for the wavelength range 1.3 - 3 Å and with suitable size, such a device can give much better efficiency than 3He cells, which are often in use. The higher flux at the sample position of a factor of at least 3.3, with lower divergence and good polarization degree from 98% (1.3 Å) to above 94% (3 Å) makes the bender set-up favorable over the layout with a 3He-cell.

The electromagnetic Sigma-to-Lambda hyperon transition form factors at low energies

.Using dispersion theory the low-energy electromagnetic form factors for the transition of a Sigma to a Lambda hyperon are related to the pion vector form factor. The additionally required input, i.e. the two-pion-Sigma-Lambda amplitudes are determined from relativistic next-to-leading-order (NLO) baryon chiral perturbation theory including the baryons from the octet and optionally from the decuplet. Pion rescattering is again taken into account by dispersion theory. It turns out that the inclusion of decuplet baryons is not an option but a necessity to obtain reasonable results. The electric transition form factor remains very small in the whole low-energy region. The magnetic transition form factor depends strongly on one not very well determined low-energy constant of the NLO Lagrangian. One obtains reasonable predictive power if this low-energy constant is determined from a measurement of the magnetic transition radius. Such a measurement can be performed at the future Facility for Antiproton and Ion Research (FAIR).

Phenomenological extraction of two-photon exchange amplitudes from elastic electron-proton scattering cross section data

In this work, I improve on and extend to low and high $Q^2$ values the extractions of the $\varepsilon$ dependence of the real parts of the two-photon exchange (TPE) amplitudes relative to the magnetic form factor, as well as the ratio $P_l/P_l^{Born} (\varepsilon,Q^2)$ by using world data on $\sigma_R(\varepsilon,Q^2)$ with an emphasis on precise new data covering the low-momentum region which is sensitive to the large-scale structure of the nucleon. I provide simple parametrizations of the TPE amplitudes, along with an estimate of the fit uncertainties. The extracted TPE amplitudes are compared with previous phenomenological extractions and TPE calculations. The $P_l/P_l^{Born}$ ratio is extracted by using the new parametrizations of the TPE amplitudes and compared to previous extractions, TPE calculations, and direct measurements at $Q^2$ = 2.50 (GeV/c)$^2$. The extracted TPE amplitudes are on the few-percentage-points level and behave roughly linearly with increasing $Q^2$ where they become nonlinear at high $Q^2$. Contrary to $Y_M$, which is influenced mainly by elastic contributions, I find $Y_E$ to be influenced by inelastic contributions at large $Q^2$ values. While $Y_E$ and $Y_3$ differ in magnitude, they have opposite sign and tend to partially cancel each other. This suggests that the TPE correction to $\sigma_R(\varepsilon,Q^2)$ is driven mainly by $Y_M$ and to a lesser extent by $Y_3$ in agreement with previous phenomenological extractions and hadronic TPE calculations.

Three-dimensional magnetic interactions in quasi-two-dimensional PdAs2O6

Millimeter-sized PdAs2O6 single crystals are grown using the vapor transport technique. The magnetic order at K is studied by measuring magnetic properties, specific heat, and neutron single crystal diffraction. The anisotropic magnetic susceptibility and a metamagnetic transition observed in magnetic fields above 20 kOe suggest that the magnetic moment lies in the ab plane, consistent with the magnetic structure determined by neutron single crystal diffraction. Below 140 K, Pd2+ ions order ferromagnetically in the ab plane but antiferromagnetically along the crystallographic c axis. The ordered moment is refined to be 2.09(2) /Pd2+ using the fitted magnetic form factor of Pd2+ . A weak λ-type anomaly around TN was observed in specific heat and the magnetic entropy change across TN is 1.72 J mol−1 K.This small entropy change and the temperature dependence of the magnetic susceptibility support the presence of short range correlations in a wide temperature range 250 K. The comparison with SrRu2O6 suggests that the magnetic interactions in PdAs2O6 are dominated by Pd-(O--O)-Pd super-superexchange and three dimensional despite the quasi-two-dimensional arrangement of magnetic ions. The comparison with NiAs2O6 suggests that increasing covalency of isostructural compounds is an effective approach to design and to discover new materials with higher magnetic order temperatures in the localized regime.

Magnetic moments and electromagnetic form factors of the decuplet baryons in chiral perturbation theory

We have systematically investigated the magnetic moments and magnetic form factors of the decuplet baryons to the next-to-next-leading order in the framework of the heavy baryon chiral perturbation theory. Our calculation includes the contributions from both the intermediate decuplet and octet baryon states in the loops. We also calculate the charge and magnetic dipole form factors of the decuplet baryons. Our results may be useful to the chiral extrapolation of the lattice simulations of the decuplet electromagnetic properties.