Search

38th International Symposium on Lattice Field Theory, LATTICE2021 , Online, United States, 26 Jul 2021 - 30 Jul 2021; Proceedings of Science / International School for Advanced Studies (LATTICE2021), 426 (2022). doi:10.22323/1.396.0426, Lattice QCD calculations of the nucleon electromagnetic form factors are of interest at both the high and low momentum transfer regions. For high momentum transfers especially there are open questions which require more intense study, such as the potential zero crossing in the proton’s electric form factor. We will present recent progress from the QCDSF/UKQCD/CSSM collaboration on the calculation of these form factors using the Feynman-Hellmann method in lattice QCD. The Feynman-Hellmann method allows for greater control over excited states which we take advantage of by going to high values of the momentum transfer. In this proceeding we present results of the form factors up to $6\ \textrm{GeV}^2$ , using $𝑁_f=2+1$ flavour fermions for three different pion masses in the range $310-470 \textrm{MeV}$. The results are extrapolated to the physical pion mass through the use of a flavour breaking expansion., Published by SISSA, Trieste

38th International Symposium on Lattice Field Theory , (LATTICE2021), Zoom/Gather@Massachusetts Institute of Technology, USA, 26 Jul 2021 - 30 Jul 2021; Proceedings of Science / International School for Advanced Studies (LATTICE2021), 250 (2022). doi:10.22323/1.396.0250, We present the nucleon axial and electromagnetic form factors using $N_\textrm{f}$=2+1+1 ensembles of twisted mass fermions with clover improvement and with masses tuned to their physical values. Excited state effects are studied using several sink-source time separations in the range 0.8 fm - 1.6 fm, exponentially increasing statistics with the separation such that statistical errors remain approximately constant. In addition, quark loop disconnected diagrams are included in order to extract the isoscalar axial form factors and the proton and neutron electromagnetic form factors, as well as their strange-quark contributions. The radii and moments are extracted by modelling the $Q^2$ dependence, including using the so-called $z$-expansion. A preliminary assessment of lattice cut-off effects is presented using two lattice spacings directly at the physical point., Published by SISSA, Trieste

A joint fit to neutrino-nucleon scattering and pion electroproduction data is performed to evaluate the nucleon axial form factor in the two-component model consisting of a three-quark intrinsic structure surrounded by a meson cloud. Further constrains on the model are obtained by re-evaluating the electromagnetic form factor using electron scattering data. The results of the axial form factor show sizable differences with respect to the widely used dipole model. The impact of such changes on the Charged-Current Quasi-Elastic neutrino-nucleus cross-section is evaluated in the SuSAv2 nuclear model, based on the Relativistic Mean Field and including the contribution of two-body currents. How the different parametrizations of the axial form factor affect the cross-section prediction is assessed in full details and comparisons to recent T2K and MINERvA data are presented., 19 pages, 12 figures

We compare the results of the SuSAv2 model including meson-exchange currents (MEC) with the recent measurement of the quasielastic-like double differential antineutrino cross section on hydrocarbon (CH) performed by the MINERvA Collaboration. The relativistic nature of the model makes it suitable to describe these data, which correspond to a mean beam energy of 3.5 GeV. The standard SuSAv2 model predictions agree well with the data without needing any additional or tuned parameter. The role of longitudinal MEC is non-negligible and improves the agreement with the data. We also consider the impact of different treatments of the $\Delta$-resonance propagator in the two-body currents on the data comparison., Comment: 9 pages, 4 figures

The study of electromagnetic transitions opens a window into the very nature of the strong interaction. And, indeed, such a study of how a ground-state nucleon transitions to an excited state, over a broad range of $$q^2$$ , will provide keen insight into the evolution of how dynamically-generated masses emerge from the asymptotically-free, nearly massless quarks of perturbative QCD as well as provide information on the ancillary effects from the meson–baryon cloud. The space-like ( $$q^20$$ ) region at GSI. We are living in exciting times whereby near-future prospects exist in extracting high-quality data in both the space-like and time-like regimes (JLab12 and FAIR, for example). The recent ECT* workshop, entitled space-like and time-like electromagnetic baryonic transitions, brought together several disparate communities of experimentalists and theorists. The goal and purpose of this workshop was to make the very first steps towards a much needed consistent description spanning the two kinematical regimes in $$q^2$$ . The discussions included photoproduction measurements (ELSA, JLab, LEPS, and MAMI), wherein the $$q^2=0$$ point anchors the connection between space-like and time-like regions and meson-beam data (GSI and J-PARC) and amply complements the requisite information for baryon spectroscopy. This paper presents the outcomes from this ECT* workshop, space-like and time-like baryon electromagnetic transitions, held at the European Centre for Theoretical Studies in Nuclear Physics and Related Areas in Trento, Italy, May 8–12, 2017.

Physical review / D 90(3), 034502 (2014). doi:10.1103/PhysRevD.90.034502, We apply a formalism inspired by heavy-baryon chiral perturbation theory with finite-range regularization to dynamical $2+1$-flavor CSSM/QCDSF/UKQCD Collaboration lattice QCD simulation results for the electric form factors of the octet baryons. The electric form factor of each octet baryon is extrapolated to the physical pseudoscalar masses, after finite-volume corrections have been applied, at six fixed values of ${Q}^{2}$ in the range $0.2–1.3\text{}\text{}{\mathrm{GeV}}^{2}$. The extrapolated lattice results accurately reproduce the experimental form factors of the nucleon at the physical point, indicating that omitted disconnected quark loop contributions are small relative to the uncertainties of the calculation. Furthermore, using the results of a recent lattice study of the magnetic form factors, we determine the ratio ${\mu }_{p}{G}_{E}^{p}/{G}_{M}^{p}$. This quantity decreases with ${Q}^{2}$ in a way qualitatively consistent with recent experimental results., Published by Soc., [S.l.]

1-22 (1974)., We have measured the spectra of electrons scattered from 6 Li and 12 C for invariant masses of the hadronic system W ≦ 1.5 GeV and four momentum transfers in the range 5 fm −2 ≦ q 2 ≦ 12 fm −2 . We compared the shape of the spectra with different nuclear models. The Fermigas model of the nucleus cannot reproduce the data. A shell model with short-range correlations fits the data with a correlation parameter q c ≈ 250 MeV/ c . From the absolute cross section the effective number of nucleons was derived for quasi-elastic scattering and found to be compatible with A , whereas the effective number of nucleons derived for the excitation of the Δ(1236) resonance was found to be 0.6 A .

43 pp. (1977).

47 pp. (1972).

Accessing hadronic form factors at large momentum transfers has traditionally presented a challenge for lattice QCD simulations. Here we demonstrate how a novel implementation of the Feynman-Hellmann method can be employed to calculate hadronic form factors in lattice QCD at momenta much higher than previously accessible. Our simulations are performed on a single set of gauge configurations with three flavours of degenerate mass quarks corresponding to $m_\pi \approx 470 \text{ MeV}$. We are able to determine the electromagnetic form factors of the pion and nucleon up to approximately $6 \text{ GeV}^2$, with results for $G_E/G_M$ in the proton agreeing well with experimental results.