Narrow Results

The nucleon has been used as a laboratory to investigate its own spin structure and quantum chromodynamics. New experimental data on nucleon spin structure at low to intermediate momentum transfers combined with existing high momentum transfer data offer a comprehensive picture of the transition region from the confinement regime of the theory to its asymptotic freedom regime. Insight for some aspects of the theory is gained by exploring lower moments of spin structure functions and their corresponding sum rules (i.e. the Gerasimov–Drell–Hearn, Bjorken and Burkhardt–Cottingham). These moments are expressed in terms of an operator-product expansion using quark and gluon degrees of freedom at moderately large momentum transfers. The sum rules are verified to good accuracy assuming that no singular behavior of the structure functions is present at very high excitation energies. The higher-twist contributions have been examined through the moments evolution as the momentum transfer varies from higher to lower values. Furthermore, QCD-inspired low-energy effective theories, which explicitly include chiral symmetry breaking, are tested at low momentum transfers. The validity of these theories is further examined as the momentum transfer increases to moderate values. It is found that chiral perturbation calculations agree reasonably well with the first moment of the spin structure function g₁ at momentum transfer of 0.1 GeV² but fail to reproduce the neutron data in the case of the generalized polarizability δ_LT.

By applying a spatially extended sink operator, the nucleon two-point functions are calculated in Coulomb gauge from quenched lattice QCD with overlap fermions. The Bethe-Salpeter wave functions of nucleon and Roper resonance are extracted at different quark masses. The typical size of nucleon is about 0.7 fm, which seems insensitive to the quark masses involved in this work. It is also found that the wave function of Roper has a radial node.

This paper presents new results for the $T_{20}$-component of the tensor analyzing power of the reaction $\gamma d\to pn{\pi }^0$ in the photon energy range of $300\mathrm{\text{MeV}}<E_{\gamma }<500\mathrm{\text{MeV}}$. The experimental statistics accumulated in 2013 at the VEPP-3 accelerator-storage complex is used. The reaction events are identified by the coincidence registration of the proton and two $\gamma$-quanta from the decay of the neutral pion. To determine the $T_{20}$-component, the asymmetry of the yields with respect to the change of sign of the tensor polarization of the deuterium target is measured. The experimental results are compared with the theoretical calculations in which the MAID 2007 model is used as the elementary pion–nucleon photoproduction amplitude and contributions from the pion–nucleon and nucleon–nucleon rescattering are taken into account.

Measurements of differential cross sections for pion-nucleon charge exchange, π^-p→π⁰n, in the region of the P₁₁(1440), or Roper, resonance are presented. These data were obtained as part of the baryon spectroscopy program using the Crystal Ball detector at the Alternating Gradient Synchrocyclotron (AGS) at Brookhaven National Laboratory (BNL). Data were taken in 1998 with a liquid hydrogen target and in 2002 with CH₂ and C targets.

By applying a spatially extended sink operator, the nucleon two-point functions are calculated in Coulomb gauge from quenched lattice QCD with overlap fermions. The Bethe-Salpeter wavefunctions of nucleon and Roper resonance are extracted at different quark masses. The typical size of nucleon is about 0.7 fm, which seems insensitive to the quark masses involved in this work. It is also found that the wavefunction of Roper has a radial node.

Within the standard $V-A$ theory of weak interactions, Quantum Electrodynamics (QED) and the linear $\sigma$-model $(\mathrm{\text{L}}\sigma \mathrm{\text{M}})$ of strong low-energy hadronic interactions we analyze gauge and infrared properties of hadronic structure of the neutron and proton in the neutron ${\beta }^{-}$-decay to leading order in the large nucleon mass expansion. We show that the complete set of Feynman diagrams describing radiative corrections of order $O(\alpha /\pi )$, induced by hadronic structure of the nucleon, to the rate of the neutron ${\beta }^{-}$-decay is gauge noninvariant and unrenormalizable. We show that a gauge noninvariant contribution does not depend on the electron energy in agreement with Sirlin’s analysis of contributions of strong low-energy interactions (Phys. Rev.164, 1767 (1967)). We show that infrared divergent and dependent on the electron energy contributions from the neutron radiative ${\beta }^{-}$-decay and neutron ${\beta }^{-}$-decay, caused by hadronic structure of the nucleon, are canceled in the neutron lifetime. Nevertheless, we find that divergent contributions of virtual photon exchanges to the neutron lifetime, induced by hadronic structure of the nucleon, are unrenormalizable even formally. Such an unrenormalizability can be explained by the fact that the effective $V-A$ vertex of hadron–lepton current–current interactions is not a vertex of the combined quantum field theory including QED and $\mathrm{\text{L}}\sigma \mathrm{\text{M}}$, which are renormalizable theories. We assert that for a consistent gauge invariant and renormalizable analysis of contributions of hadronic structure of the nucleon to the radiative corrections of any order to the neutron decays one has to use a gauge invariant and fully renormalizable quantum field theory including the Standard Electroweak Model (SEM) and the $\mathrm{\text{L}}\sigma \mathrm{\text{M}}$, where the effective $V-A$ vertex of hadron–lepton current–current interactions is caused by the $W^{-}$-electroweak-boson exchange.

The axial-vector form factor of the nucleons is studied at a finite temperature using the holographic soft-wall model with the thermal dilaton field. We use the bulk interaction action known from the zero temperature case and apply the profile functions of fields thermalized by the interaction with the thermal dilaton field. The dependence of the axial form factor on the square of the transferred momentum and the temperature is plotted for the ground and excited states of the nucleons.

Nucleon structure study is one of the most important research areas in modern physics and has challenged us for decades. Spin has played an essential role and often brought surprises and puzzles to the investigation of the nucleon structure and the strong interaction. New experimental data on nucleon spin structure at low to intermediate momentum transfers combined with existing high momentum transfer data offer a comprehensive picture in the strong region of the interaction and of the transition region from the strong to the asymptotic-free region. Insight into some aspects of the theory for the strong interaction, Quantum Chromodynamics (QCD), is gained by exploring lower moments of spin structure functions and their corresponding sum rules (i.e., the Bjorken, Burkhardt–Cottingham, Gerasimov–Drell–Hearn (GDH), and the generalized GDH). These moments are expressed in terms of an operator-product expansion using quark and gluon degrees of freedom at moderately large momentum transfers. The higher-twist contributions have been examined through the evolution of these moments as the momentum transfer varies from higher to lower values. Furthermore, QCD-inspired low-energy effective theories, which explicitly include chiral symmetry breaking, are tested at low momentum transfers. The validity of these theories is further examined as the momentum transfer increases to moderate values. It is found that chiral perturbation theory calculations agree reasonably well with the first moment of the spin structure function g₁ at low momentum transfer of 0.05–0.1 GeV² but fail to reproduce some of the higher moments, noticeably, the neutron data in the case of the generalized polarizability δ_LT. The Burkhardt–Cottingham sum rule has been verified with good accuracy in a wide range of Q² assuming that no singular behavior of the structure functions is present at very high excitation energies.

In the Skyrme model of nucleons and nuclei, the spin excitation energy of the nucleon is traditionally calculated by a fit of the rigid rotor quantization of spin/isospin of the fundamental Skyrmion (the hedgehog) to the masses of the nucleon and the Delta resonance. The resulting, quite large spin excitation energy of the nucleon of about $73\mathrm{\text{MeV}}$ is, however, rather difficult to reconcile with the small binding energies of physical nuclei, among other problems. Here, we argue that a more reliable interval of values for the spin excitation energy of the nucleon, compatible with many physical constraints is between $15\mathrm{\text{MeV}}$ and $30\mathrm{\text{MeV}}$. The fit of the rigid rotor to the Delta, on the other hand, is problematic in any case, because it implies the use of a nonrelativistic method for a highly relativistic system.

All three components of the tensor analyzing power for the reaction of ${\pi }^{-}$-meson photoproduction on a deuteron have been measured in photon energy range of 280–500MeV and proton energy range of 15–70MeV. The experiment has been conducted on an internal tensor-polarized deuterium gas target of the VEPP-3 electron storage ring using the method of detecting two final protons in coincidence. Measured components of the tensor analyzing power have been compared with calculations results obtained within the framework of diagrammatic approach.

The paper discusses the results of measurement for three components of tensor analyzing power for the reaction of incoherent ${\pi }^0$-meson photoproduction on a deuteron within the proton energy range of 15–200MeV and the neutron energy range of 15–150MeV. The experiment was performed on the deuterium internal gas target of VEPP-3 electron accelerator using the protons and neutrons coincidence counting technique. The results of measurements of the tensor analyzing power’s components are compared with the results of statistical modeling performed within the frameworks of a theoretical model.

The paper presents the results of measurements of the tensor analyzing power component $T_{20}$ for the coherent neutral pion photoproduction on the deuteron. The measurements were performed in the Budker Institute of Nuclear Physics using the internal tensor polarized deuterium target at VEPP-3 storage ring. The measurements covered the region of the photon energy 240 — 420MeV and the region of the center-of-mass pion polar angle 100–140${}^{\circ }$. The results of measurements were compared with the calculations performed within frameworks of several theoretical models.

During years 2011 and 2012 data taking runs have been carried out at VEPP-2000 e⁺e^- collider to measure the production of the nucleon-antinucleon pairs near threshold. In this talk the preliminary results on the nucleon timelike electromagnetic form factors (FF) and the |G_E/G_M| ratio are presented.

The physics of the nucleon form factors is the basic part of the Jefferson Laboratory program. We review the achievements of the 6-GeV era and the program with the 12-GeV beam with the SBS spectrometer in Hall A, with a focus on the nucleon ground state properties.

Spin-physics projects at J-PARC are explained by including future possibilities. J-PARC is the most-intense hadron-beam facility in the high-energy region above multi-GeV, and spin physics will be investigated by using secondary beams of kaons, pions, neutrinos, muons, and antiproton as well as the primary-beam proton. In particle physics, spin topics are on muon $g-2$, muon and neutron electric dipole moments, and time-reversal violation experiment in a kaon decay. Here, we focus more on hadron-spin physics as for future projects. For example, generalized parton distributions (GPDs) could be investigated by using pion and proton beams, whereas they are studied by the virtual Compton scattering at lepton facilities. The GPDs are key quantities for determining the three-dimensional picture of hadrons and for finding the origin of the nucleon spin including partonic orbital-angular-momentum contributions. In addition, polarized parton distributions and various hadron spin topics should be possible by using the high-momentum beamline. The strangeness contribution to the nucleon spin could be also investigated in principle with the neutrino beam with a near detector facility.

The nucleon is the main building blocks of our visible universe. The electro-magnetic form factors serve as the structure observables as well as the test ground for strong interaction. The hyperons, on the other hand, provide a new perspective to dissect the structure of neuclon by replacing one or two quarks into stranges. In this proceeding, I will introduce a series of results obtained from BESIII experiment for the baryon form factors in time-like including both nucleon and hyperon. Furthermore, the prospect of the studies for baryon form factors at BESIII is presented.

The nucleon spin structure has been an active, exciting and intriguing subject of interest for the last three decades. Recent experimental data on nucleon spin structure at low to intermediate momentum transfers provide new information in the confinement regime and the transition region from the confinement regime to the asymptotic freedom regime. New insight is gained by exploring moments of spin structure functions and their corresponding sum rules (i.e. the generalized Gerasimov-Drell-Hearn, Burkhardt-Cottingham and Bjorken). The Burkhardt-Cottingham sum rule is verified to good accuracy. The spin structure moments data are compared with Chiral Perturbation Theory calculations at low momentum transfers. It is found that chiral perturbation calculations agree reasonably well with the first moment of the spin structure function g₁ at momentum transfer of 0.05 to 0.1 GeV² but fail to reproduce the neutron data in the case of the generalized polarizability δ_LT (the δ_LT puzzle). New data have been taken on the neutron (³He), the proton and the deuteron at very low Q² down to 0.02 GeV². They will provide benchmark tests of Chiral dynamics in the kinematic region where the Chiral Perturbation theory is expected to work.

A feasibility study has been made for an experiment to greatly extend the Q²-range of precision measurements of the neutron's magnetic form factor using the existing JLab 6 GeV beam. The results are promising.

In this note, we briefly review our recent works related to the holographic nucleon’s spectrum in the nuclear medium. In order to describe the nuclear medium holographically, we introduce a charged thermal AdS space and investigate fermion fluctuation corresponding nucleon on this background.

We explain the origin of the controversy about the existence of a transverse angular momentum sum rule, and show that it stems from utilizing an incorrect result in the literature, concerning the expression for the expectation values of the angular momentum operators. We demonstrate a new, short and direct way of obtaining correct expressions for these expectation values, from which a perfectly good transverse angular momentum sum rule can be deduced. We also introduce a new classification of sum rules into primary and secondary types. In the former all terms occurring in the sum rule can be measured experimentally; in the latter some terms cannot be measured experimentally.