[en] Neutrons and protons are the main building blocks of atomic nuclei and neutrons have been used to probe nuclear structure since the pioneering days of nuclear physics. As strongly interacting hadrons they have a high probability of reaction and, being uncharged, they are unaffected by the nuclear Coulomb field. Neutron scattering for example has been used to determine nuclear sizes and shapes. However the strong interaction inhibits the neutron from penetrating the surface skin of the nucleus and to gain information on the interior a relatively weakly interacting probe such as a photon or electron is superior.As the energies of electron accelerators have increased, shorter distances may be probed, until at a photon momentum of ∼200 MeV/c the reduced wavelength is 1 fm, roughly the dimension of the neutron or proton. From this point one starts to become sensitive to the internal structure. Until recently most experiments have concentrated on the proton as a hydrogen target is experimentally straightforward. There is of course no free neutron target, but with an improved understanding of how nuclear binding affects the neutron embedded in deuterium or helium-3, these materials may be considered as effective neutron targets. The extra information obtained from examining an up-down-down-quark neutron, as opposed to an up-up-down-quark proton, will be vital to achieve a full understanding of the ways in which elementary quarks and gluons interact to make composite hadrons. New results from the MAMI accelerator in Germany are presented and an extension of these measurements at Jefferson Laboratory in the USA is previewed.As well as being pivotal to the development of fundamental nuclear physics, neutrons have immense technological importance. Many of the early neutron scattering experiments were driven by a need to understand nuclear fission processes for power generation or weapons production, but neutron beams have also been widely used in medicine for the treatment of cancerous tumours. Nowadays photon-beam radiotherapy is more common, but neutron photo-production constitutes a significant source of secondary dose received during a course of treatment. The programme to measure these effects at Lund in Sweden is described, along with methods of calculating neutron dose in tissue using nuclear-physics techniques originally developed to obtain the response of neutron detectors

[en] Here, the unpolarized semi-inclusive deep-inelastic scattering (SIDIS) differential cross sections in "3He(e,e'π"±)X have been measured for the first time in Jefferson Lab experiment E06-010 with a 5.9 GeV e"– beam on a "3He gas target. The experiment focuses on the valence quark region, covering a kinematic range 0.12 < x_b_j < 0.45,1 < Q"2 < 4(GeV/c)"2,0.45 < z_h < 0.65, and 0.05 < P_t < 0.55GeV/c. The extracted SIDIS differential cross sections of π± production are compared with existing phenomenological models while the "3He nucleus approximated as two protons and one neutron in a plane-wave picture, in multidimensional bins. Within the experimental uncertainties, the azimuthal modulations of the cross sections are found to be consistent with zero.

[en] The electromagnetic polarizabilities of the nucleon are fundamental nucleon-structure observables that characterize its response to external electromagnetic fields. The neutron polarizabilities can be accessed from Compton-scattering data on light nuclear targets. Recent measurements of the differential cross section for Compton scattering on the deuteron below the pion-production threshold have decreased the uncertainties in the neutron polarizabilities, yet the proton polarizabilities remain known substantially more accurately. As the sensitivity of the cross section to the polarizabilities increases with incident photon energy, measurements above the pion threshold may offer a way for an improved determination of the neutron polarizabilities. In this work, the first measurement of the cross section for Compton scattering on the deuteron above the pion-production threshold is presented.

[en] Here, we report the measurement of beam-target double-spin asymmetries A_LT in the inclusive production of identified hadrons, e +³He^↑ → h + X, using a longitudinally polarized 5.9 GeV electron beam and a transversely polarized ³He target. Hadrons (π^±, K^± and proton) were detected at 16° with an average momentum $\langle P_h\rangle =2.35$ GeV/c and a transverse momentum (p_T) coverage from 0.60 to 0.68 GeV/c. Asymmetries from the ³He target were observed to be non-zero for π^± production when the target was polarized transversely in the horizontal plane. The π⁺ and π^- asymmetries have opposite signs, analogous to the behavior of A_LT in semi-inclusive deep-inelastic scattering..

[en] An experimental study of the η' → π ⁰π ⁰η → 6$\mathrm{\gamma <!--\; ??\; -->}$ decay has been conducted with the best up- to-date statistical accuracy, by measuring η' mesons produced in the $\mathrm{\gamma <!--\; ??\; -->}$p → η'p reaction with the A2 tagged-photon facility at the Mainz Microtron, MAMI. The results obtained for the standard parametrization of the η' → π ⁰π ⁰η matrix element are consistent with the most recent results for η' → ππη decays, but have smaller uncertainties. Finally, the available statistics and experimental resolution allowed, for the first time, an observation of a structure below the π ⁺π ^- mass threshold, the magnitude and sign of which, checked within the framework of the nonrelativistic effective-field theory, demonstrated good agreement with the cusp that was predicted based on the ππ scattering length combination, a ₀ - a ₂, extracted from K → 3π decays. Authors:

[en] A direct measurement of the helicity dependence of the total photoabsorption cross section on the proton was carried out at MAMI (Mainz) in the energy range 200< E_γ<800 MeV . The experiment used a 4π detection system, a circularly polarized tagged photon beam, and a frozen spin target. The contributions to the Gerasimov-Drell-Hearn sum rule and to the forward spin polarizability γ₀ determined from the data are 226±5(stat)±12(syst) μb and -187±8(stat)±10(syst) x 10^-6 fm⁴ , respectively, for 200< E_γ<800 MeV

[en] An experiment that aims to measure the π"− photoproduction cross-section σ(E) on the deuteron γ + "2H → π"− + 2p near threshold is discussed. The main concepts of the experimental technique are presented alongside some preliminary signals.

[en] Here we correct a factor of 2 missed in one of figures and the corresponding sentence in the text. It does not change any conclusions.

[en] We present the first detailed measurement of incoherent photoproduction of neutral pions to a discrete state of a residual nucleus. The ¹²C(γ,π⁰)¹²C_4.4MeV* reaction has been studied with the Glasgow photon tagger at MAMI employing a new technique which uses the large solid angle Crystal Ball detector both as a π⁰ spectrometer and to detect decay photons from the excited residual nucleus. The technique has potential applications to a broad range of future nuclear measurements with the Crystal Ball and similar detector systems elsewhere. Such data are sensitive to the propagation of the Δ in the nuclear medium and will give the first information on matter transition form factors from measurements with an electromagnetic probe. The incoherent cross sections are compared to two theoretical predictions including a Δ-hole model

[en] A comprehensive set of ⁴He(γ,n) absolute cross-section measurements was performed at MAX-lab in Lund, Sweden. Tagged photons from 23< E_γ<70 MeV were directed toward a liquid ⁴He target, and neutrons were identified using pulse-shape discrimination and the time-of-flight technique in two liquid-scintillator detector arrays. Seven-point angular distributions have been measured for 14 photon energies. The results have been subjected to complementary transition-coefficient and Legendre-coefficient analyses. The results are also compared to experimental data measured at comparable photon energies as well as recoil-corrected continuum shell-model, resonating group method, and effective interaction hyperspherical-harmonic expansion calculations. For photon energies below 29 MeV, the angle-integrated data are significantly larger than the values recommended by Calarco, Berman, and Donnelly in 1983