Electromagnetic Form Factors Research Articles

In-medium electromagnetic form factors and spin polarizations

In-medium electromagnetic form factors and spin polarizations

Radiative transition decay width of ψ2(3823)→γχc1 from lattice QCD

We present an exploratory Nf=2 lattice QCD study of ψ2(3823)→γχc1 at a pion mass mπ≈350 MeV. The related two-point and three-point functions are calculated using the distillation method. The electromagnetic multipole form factor V^(0)=2.083(11) for J/ψ→γηc is consistent with previous lattice results. The form factors E^1(0), M^2(0), and E^3(0) for Γ(χc2→γJ/ψ) have the same hierarchy as that derived from experiments, and the predicted decay width Γ(χc2→γJ/ψ)=368(5) keV is in excellent agreement with the Particle Data Group value 374(10) keV and previous lattice QCD results in the quenched approximation. The same strategy is applied to the study of the process ψ2(3823)→γχc1, and the partial decay width is predicted to be 337(27) keV. According to the BESIII constraints on the ψ2(3823) decay channels and some phenomenological results, we estimate the total width Γ(ψ2(3823))=520(100) keV. Published by the American Physical Society 2024

Algebraic model to study the internal structure of pseudoscalar mesons with heavy-light quark content

The internal structure of all lowest-lying pseudoscalar mesons with heavy-light quark content is studied in detail using an algebraic model that has been applied recently, and successfully, to the same physical observables of pseudoscalar and vector mesons with hidden-flavor quark content, from light to heavy quark sectors. The algebraic model consists on constructing simple and evidence-based of the meson’s Bethe-Salpeter amplitude (BSA) and quark’s propagator in such a way that the Bethe-Salpeter wave function (BSWF) can then be readily computed algebraically. Its subsequent projection onto the light front yields the light front wave function (LFWF) whose form allows us a simple access to the valence-quark parton distribution amplitude (PDA) by integrating over the transverse momentum squared. We exploit our current knowledge of the PDAs of lowest-lying pseudoscalar heavy-light mesons to compute their generalized parton distributions (GPDs) through the overlap representation of LFWFs. From these three dimensional knowledge, different limits/projections lead us to deduce the related parton distribution functions (PDFs), electromagnetic form factors (EFFs), and impact parameter space GPDs (IPS-GPDs). When possible, we make explicit comparisons with available experimental results and earlier theoretical predictions. Published by the American Physical Society 2024

Inside the Nucleon: Tomographic Interpretations and Universality of GPDs with DDVCS

The goal of Double Deeply Virtual Compton Scattering (DDVCS) experiments is to better understand the internal structure of the nucleon. Previous attempts to resolve the internal structure of nucleons have resulted in electromagnetic form factors and parton distribution functions for elastic scattering and deep inelastic scattering processes, respectively. Generalized Parton Distributions (GPDs) are the latest attempt to unify these models of nucleon structure. The GPDs of DDVCS give us ability to investigate off of the diagonal where x ̸= ±ξ. The main goal of our analysis is to determine the best experimental setup in order to deduce the kinematic variables on which GPDs depend from the lab observables. The effectiveness of our data collection in the laboratory is by determined the physical kinematics, Q2, Q′2,t, xi,ϕLM, ϕCMV , and θCMV . We can then run DDVCS experiments and collect data on observables to improve upon the current models for GPDs of the nucleon.

Recent results of Baryon electromagnetic form factors at BESIII

Baryon Electromagnetic Form Factors are essential for testing ground state models of nucleon internal structures. At the BESIII experiment, a comprehensive study has been conducted on the electromagnetic form factors of various baryons. The electromagnetic form factor ratio of the nucleon (proton and neutron), denoted as |GE/GM|, has been determined with high precision. And the study at BESIII has explored the cross sections of various baryon pairs, including Λ, Λc, Σ, Ξ, Ω and Δ from their respective thresholds. In the study conducted at BESIII, threshold effects have been observed in some baryon pairs, enhancing our understanding of these baryon interactions.

N*(1520) transition form factors from dispersion theory

The electromagnetic transition form factors (TFFs) of the nucleon provide important information on the internal structure of hadrons. A model-independent dispersive calculation of the electro magnetic TFFs N*(1520) → N at low energies is presented. Taking pion rescattering into consideration, we derived dispersive relations for the N*(1520) → N TFFs that relate space-like and time-like regions from the first principles. Based on the space-like data from JLab and hadronic data measured by HADES, we make predictions for TFFs in the time-like region. Our predictions can be tested in future experi ments (e.g. HADES).

Hyperon production and interaction studies in protonproton scattering with HADES

Hyperons and their interactions with baryonic matter may play a key role in our understanding of the core of neutron stars. Moreover, the internal structure of hyperons and their excitations are of great interest. Their structure can be probed by exploiting their couplings to radiative probes such as by measuring electromagnetic transition form factors. HADES (High-Acceptance Di-Electron Spectrometer) at GSI collected high-statistics proton-proton scattering data in 2022 at √s = 3.48 GeV. The Λ - Λ interaction is currently being studied in this data along with production of Σ states where the Dalitz decay of hyperons might be observed for the first time. In addition, the reaction pp → pK+K+Ξ−[π−Λ[pπ−]] has been studied to probe the production mechanism of double strangeness near its production threshold. This proceeding addresses the hyperon physics case and discusses the ongoing Ξ− analysis. A preliminary upper limit for the cross section at √s = 3.48 GeV is presented taking into account only statistical uncertainties.

At the heart of the proton

Two main findings on electromagnetic hadron form factors focussed a large interest of the hadron physics community in the recent years. One is the decrease of the electric to magnetic form factor ratio when the momentum transfer in electron proton elastic scattering increases. The second is the discovery of regular oscillations of the generalized proton form factors in the annihilation process electron-positron into proton-antiproton. In this talk we propose a coherent interpretation of these findings giving a general, dynamical description of the proton in the space-time frame which is based on the presence of a quantum vacuum at very small distances.

Neutral Pion Electromagnetic Form Factor as a Bound System of 3 + 1 Dimensional QCD

Neutral Pion Electromagnetic Form Factor as a Bound System of 3 + 1 Dimensional QCD

Proton and neutron electromagnetic radii and magnetic moments from lattice QCD

We present results for the electromagnetic form factors of the proton and neutron computed on the (2 + 1)-flavor Coordinated Lattice Simulations (CLS) ensembles including both quark-connected and -disconnected contributions. The Q2-, pion-mass, lattice-spacing, and finite-volume dependence of our form factor data is fitted simultaneously to the expressions resulting from covariant chiral perturbation theory including vector mesons amended by models for lattice artefacts. From these fits, we determine the electric and magnetic radii and the magnetic moments of the proton and neutron, as well as the Zemach radius of the proton. To assess the influence of systematic effects, we average over various cuts in the pion mass and the momentum transfer, as well as over different models for the lattice-spacing and finite-volume dependence, using weights derived from the Akaike Information Criterion (AIC).

Looking forward to inelastic DM with electromagnetic form factors at FASER and beam dump experiments

Looking forward to inelastic DM with electromagnetic form factors at FASER and beam dump experiments

Light quark mass dependence of nucleon electromagnetic form factors in dispersively modified chiral perturbation theory

Light quark mass dependence of nucleon electromagnetic form factors in dispersively modified chiral perturbation theory

Electromagnetic form factors at low energy elastic electron–proton scattering

The prediction of quantum electrodynamics for elastic electron–proton scattering needs further modifications to agree with experimental data. Two scattering mechanisms that may occur are the forward and backward scattering angles for four-momentum transfer [Formula: see text] up to 0.8 (GeV/[Formula: see text])2. This is due to two different scattering centers. But the forward scattering is observed only at relatively high values of [Formula: see text][Formula: see text](GeV/[Formula: see text])2. The modifications related to the electric and magnetic form factors characterize the proton’s internal structure. These form factors’ dependence on [Formula: see text] provides good agreement with other analysis methods. The proton’s charge radius, which corresponds to the maximum value of the scattering radius, is [Formula: see text][Formula: see text]fm. The scattered electron is sensitive to proton internal constituents, especially at high values of [Formula: see text] in which both scattering radius and photon wavelength decrease.

Dispersive analysis of the experimental data on the electromagnetic form factor of charged pions at spacelike momenta

Dispersive analysis of the experimental data on the electromagnetic form factor of charged pions at spacelike momenta

Baryon electromagnetic form factors at BESIII

The electromagnetic form factors (EMFFs) of various baryons have been studied at BESIII. The proton EMFF ratio |GE/GM| is determined precisely. Recent results of neutron EMFFs show great improvement comparing with previous experiments. Cross sections of various baryon pairs (Λ, Σ, Ξ, Λc) are studied from their thresholds and threshold effects are observed.

Electromagnetic radii of the nucleon in soft-wall holographic QCD

We revisit the electromagnetic form factors of the proton and neutron in the original-minimal soft-wall holographic QCD, which has only two parameters, i.e., the mass scale κ and the twist parameter of the nucleon τ. We first fix τ=3 by the hard scattering rule, and extract κ=0.402 GeV from the world data (including the Mainz A1 data) of the Sachs magnetic form factor of the proton GMp. We then predict among others, the charge radius of the proton to be rp=0.831±0.008 fm, in perfect agreement with the recent charge radius of the proton measured by the PRad collaboration at Jefferson Lab, and in agreement with the muonic hydrogen experiments. Our prediction for the proton elastic form factor ratio μpGEp/GMp is also in very good agreement with the recent high precision Jefferson Lab recoil polarization experiment E08-007 for Q2=0.3−0.6 GeV2, and with the recent high precision Mainz A1 experiment for Q2<0.13 GeV2.

Measurement of polarization transfer in the quasi-elastic [formula omitted] process

Polarization transfer to a bound proton in polarized electron knock-out reactions, A(e→,e′p→), is a powerful tool to look for an in-medium modification of the bound proton. It requires comparison to calculations that consider the many-body effects accompanying the quasi-free process. We report here measured components Px′, Pz′, and their ratio Px′/Pz′, of polarization transfer to protons bound in Ca40, which is described well by the shell model and for which reliable calculations are available. While the calculations capture the essence of the data, our statistical precision allows us to observe deviations that cannot be explained by simple scaling, including by varying the proton electromagnetic form factor ratio GE/GM. We further explore the deviations of the ratio of the polarization transfer components from that of a free proton, (Px′/Pz′)A/(Px′/Pz′)H, and its dependence on the bound-proton virtuality.

Impact of NNLO QED corrections on lepton-proton scattering at MUSE

We present the complete next-to-next-to-leading order (NNLO) pure pointlike QED corrections to lepton-proton scattering, including three-photon-exchange contributions, and investigate their impact in the case of the MUSE experiment. These corrections are computed with no approximation regarding the energy of the emitted photons and taking into account lepton-mass effects. We contrast the NNLO QED corrections to known next-to-leading order corrections, where we include the elastic two-photon exchange (TPE) through a simple hadronic model calculation with a dipole ansatz for the proton electromagnetic form factors. We show that, in the low-momentum-transfer region accessed by the MUSE experiment, the improvement due to more sophisticated treatments of the TPE, including inelastic TPE, is of similar if not smaller size than some of the NNLO QED corrections. Hence, the latter have to be included in a precision determination of the low-energy proton structure from scattering data, in particular for electron-proton scattering. For muon-proton scattering, the NNLO QED corrections are considerably smaller.

Pseudoscalar current and covariance with the light-front approach

Quantum Field Theory (QFT) is used to describe the physics of particles in terms of their fundamental constituents. The Light-Front Field Theory (LFFT), introduced by Paul Dirac in 1949 [1], is an alternative approach to solve some of the problems that arise in quantum field theory. The LFFT is similar to the Equal Time Quantum Field Theory (EQT), however, some particularities are not, such as the loss of covariance in the light-front. Pion electromagnetic form factor is studied in this work at lower and higher momentum transfer regions to explore the constituent quark models and the differences among these and other models. The electromagnetic current is calculated with both the “plus” and “minus” components in the light-front approach. The results are compared with other models, as well as with experimental data.

New insights into the oscillations of the nucleon electromagnetic form factors

The electromagnetic form factors of the proton and the neutron in the timelike region are investigated. Electron–positron annihilation into antinucleon-nucleon (N¯N) pairs is treated in distorted wave Born approximation, including the final-state interaction in the N¯N system. The latter is obtained by a Lippmann–Schwinger equation for N¯N potentials derived within SU(3) chiral effective field theory. By fitting to the phase shifts and (differential) cross section data, a high quality description is achieved. With these amplitudes, the oscillations of the electromagnetic form factors of the proton and the neutron are studied. It is found that each of them can be described by two fractional oscillators. One is characterized as “overdamped” and dominates near the threshold, while the other is “underdamped” and plays an important role in the high-energy region. These two oscillators are essential to understand the distributions of polarized electric charges induced by hard photons for the nucleons.