Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userForm factors for the Nucleon-to-Roper electromagnetic transition at large-$Q^2$
91
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report on a recent calculation of all Roper-related electromagnetic transtions form factors, covering the range of energies that next-to-come planned experiments are expected to map. Direct reliable calculations were performed, within a Poincare covariant approach of the three-body bound-state problem, up to $Q^2/m^2_N$=6; approximated then by applying the Schlessinger point method and the results eventually extended up to $Q^2/m^2_Nsimeq$12 via analytic continuation.
rate research
Read More
We compute nucleon and Roper e.m. elastic and transition form factors using a symmetry-preserving treatment of a contact-interaction. Obtained thereby, the e.m. interactions of baryons are typically described by hard form factors. In contrasting this behaviour with that produced by a momentum-dependent interaction, one achieves comparisons which highlight that elastic scattering and resonance electroproduction experiments probe the infrared evolution of QCDs running masses; e.g., the existence, and location if so, of a zero in the ratio of nucleon Sachs form factors are strongly influenced by the running of the dressed-quark mass. In our description of baryons, diquark correlations are important. These correlations are instrumental in producing a zero in the Dirac form factor of the protons d-quark; and in determining d_v/u_v(x=1), as we show via a formula that expresses d_v/u_v(x=1) in terms of the nucleons diquark content. The contact interaction produces a first excitation of the nucleon that is constituted predominantly from axial-vector diquark correlations. This impacts greatly on the gamma*p->P_{11}(1440) form factors. Notably, our quark core contribution to F_2*(Q^2) exhibits a zero at Q^2~0.5mN^2. Faddeev equation treatments of a hadrons quark core usually underestimate its magnetic properties, hence we consider the effect produced by a dressed-quark anomalous e.m. moment. Its inclusion much improves agreement with experiment. On the domain 0<Q^2<2GeV^2, meson-cloud effects are important in making a realistic comparison between experiment and hadron structure calculations. Our computed helicity amplitudes are similar to the bare amplitudes in coupled-channels analyses of the electroproduction process. Thus supports a view that extant structure calculations should directly be compared with the bare-couplings, etc., determined via coupled-channels analyses.
The spatial distribution of charge and magnetization within the nucleon (proton and neutron) is encoded in the elastic electromagnetic form factors $G_E^{(p,n)}$ and $G_M^{(p,n)}$. These form factors have been precisely measured utilizing elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up- and down-quark contributions to the nucleon form factors. We expand on our original analyses and extract the up- and down-quark contributions to the nucleon electromagnetic form factors from worldwide data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. From these, we construct the flavor-separated Dirac and Pauli form factors and their ratios, and compare the results to recent extractions and theoretical calculations and models.
The role of the strange quarks on the low-energy interactions of the proton can be probed through the strange electromagnetic form factors. Knowledge of these form factors provides essential input for parity-violating processes and contributes to the understanding of the sea quark dynamics. We determine the strange electromagnetic form factors of the nucleon within the lattice formulation of Quantum Chromodynamics using simulations that include light, strange and charm quarks in the sea all tuned to their physical mass values. We employ state-of-the-art techniques to accurately extract the form factors for values of the momentum transfer square up to 0.8~GeV$^2$. We find that both the electric and magnetic form factors are statistically non-zero. We obtain for the strange magnetic moment $mu^s=-0.017(4)$, the strange magnetic radius $langle r^2_M rangle^s=-0.015(9)$~fm$^2$, and the strange charge radius $langle r^2_E rangle^s=-0.0048(6)$~fm$^2$.
The spatial distribution of charge and magnetization within the proton is encoded in the elastic form factors. These have been precisely measured in elastic electron scattering, and the combination of proton and neutron form factors allows for the separation of the up- and down-quark contributions. In this work, we extract the proton and neutron form factors from worlds data with an emphasis on precise new data covering the low-momentum region, which is sensitive to the large-scale structure of the nucleon. From these, we separate the up- and down-quark contributions to the proton form factors. We combine cross section and polarization measurements of elastic electron-proton scattering to separate the proton form factors and two-photon exchange (TPE) contributions. We combine the proton form factors with parameterization of the neutron form factor data and uncertainties to separate the up- and down-quark contributions to the protons charge and magnetic form factors. The extracted TPE corrections are compared to previous phenomenological extractions, TPE calculations, and direct measurements from the comparison of electron and positron scattering. The flavor-separated form factors are extracted and compared to models of the nucleon structure. With the inclusion of the precise new data, the extracted TPE contributions show a clear change ofsign at low $Q^2$, necessary to explain the high-$Q^2$ form factor discrepancy while being consistent with the known $Q^2 to 0$ limit. We find that the new Mainz data yield a significantly different result for the proton magnetic form factor and its flavor-separated contributions. We also observe that the RMS radius of both the up- and down-quark distributions are smaller than the RMS charge radius of the proton.
We present a unified description of elastic and transition form factors involving the nucleon and its resonances; in particular, the $N(1440)$, $Delta(1232)$ and $Delta(1600)$. We compare predictions made using a framework built upon a Faddeev equation kernel and interaction vertices that possess QCD-kindred momentum dependence with results obtained using a confining, symmetry-preserving treatment of a vector$,otimes,$vector contact-interaction in a widely-used leading-order (rainbow-ladder) truncation of QCDs Dyson-Schwinger equations. This comparison explains that the contact-interaction framework produces hard form factors, curtails some quark orbital angular momentum correlations within a baryon, and suppresses two-loop diagrams in the elastic and transition electromagnetic currents. Such defects are rectified in our QCD-kindred framework and, by contrasting the results obtained for the same observables in both theoretical schemes, shows those objects which are most sensitive to the momentum dependence of elementary quantities in QCD.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
