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Register a new userRoles of Direct Break-up Reaction on Neutrino Scattering off $^{12}$C near Nucleon Threshold Region
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Neutrino (antineutrino) scattering off $^{12}$C is one of various important key reactions for $ u$-process in the nucleosysnthesis of light nuclei. Most of neutrino-nucleus scattering are considered through indirect processes within the energy range from a few to tens of MeV. Target nuclei are excited by incident neutrino (antineutrino) through various transitions, and subsequently decay into other nuclei with emitting particles. But, direct processes are also feasible, in which incident neutrino (antineutrino) strips directly one nucleon from target nuclei. Consequently, direct processes may affect abundances of $^{11}$C and $^{11}$B additionally to indirect processes. We investigate direct neutrino (antineutrino) quasi-elastic scattering off $^{12}$C around the energy region liberating one nucleon and discuss implications of direct processes in the nucleosynthesis. The direct processes might be comparable to the indirect processes if the final state interaction is taken into account.
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We investigate the roles of chiral three-nucleon force (3NF) in nucleon-nucleus elastic scattering, using the standard framework based on the Brueckner-Hartree-Fock method for nuclear matter and the $g$-matrix folding model for the nucleon-nucleus scattering. In nuclear matter, chiral 3NF at NNLO level (mainly the 2$pi$-exchange diagram) makes the single particle potential less attractive for the singlet-even channel and more absorptive for the triplet channels. The single-particle potential calculated from chiral two-nucleon force (2NF) at N$^{3}$LO level is found to be close to that from Bonn-B 2NF. The Melbourne $g$-matrix interaction is a practical effective interaction constructed by localizing the $g$-matrices calculated from Bonn-B 2NF. We then introduce the chiral-3NF effects to the local Melbourne $g$-matrix interaction. For nucleon-nucleus elastic scattering on various targets at 65 MeV, chiral 3NF makes the folding potential less attractive and more absorptive. The novel property for the imaginary part is originated in the enhancement of tensor correlations due to chiral 3NF. The two effects are small for differential cross sections and vector analyzing powers at the forward and middle angles where the experimental data are available. If backward measurements are done, the data will reveal the effects of chiral 3NF.
Excitation spectra of $^{11}$C were measured in the $^{12}$C$(p,d)$ reaction near the $eta$ emission threshold. A proton beam extracted from the synchrotron SIS-18 at GSI with an incident energy of 2.5 GeV impinged on a carbon target. The momenta of deuterons emitted at 0 degrees were precisely measured with the fragment separator FRS operated as a spectrometer. In contrast to theoretical predictions on the possible existence of deeply bound $eta$ mesic states in carbon nuclei, no distinct structures were observed associated with the formation of bound states. The spectra were analyzed to set stringent constraints on the formation cross section and on the hitherto barely-known $eta$-nucleus interaction.
The nucleon form factors in free space are usually thought to be modified when a nucleon is bound in a nucleus or immersed in a nuclear medium. We investigate effects of the density-dependent axial and weak-vector form factors on the electro-neutrino ($ u_e$) and anti-electro-neutrino $({bar u_e})$ reactions via neutral current (NC) for a nucleon in nuclear medium or $^{12}$C. For the density-dependent form factors, we exploit the quark-meson-coupling (QMC) model, and apply them to the $ u_e$ and ${bar u_e}$ induced reactions by NC. About 12% decrease of the total cross section by $ u_e$ reaction on the nucleon is obtained at normal density, $rho = rho_0 sim 0.15 {fm}^{-3} $, as well as about 18% reduction of total ${ u}_e$ cross section on $^{12}$C, by the modification of the weak form factors of the bound nucleon. However, similarly to the charged current reaction, effects of the nucleon property change in the ${bar u}_e$ reaction reduce significantly the cross sections about 30% for the nucleon in matter and $^{12}$C cases. Such a large asymmetry in the ${bar u}_e$ cross sections is addressed to originate from the different helicities of ${bar u}_e$ and ${ u}_e$.
In this work, we study charged current quasi elastic scattering of muon anti-neutrino off nucleon and nucleus using a formalism based on Llewellyn Smith (LS) model. Parameterizations by Galster et al. are used for electric and magnetic Sachs form factors of nucleons. We use Fermi gas model along with Pauli suppression condition to take into account the nuclear effects in anti-neutrino - nucleus QES. We calculate muon anti-neutrino-p and muon anti-neutrino-^{12}C charged current quasi elastic scattering differential and total cross sections for different values of axial mass M_{A} and compare the results with data from GGM, SKAT, BNL, NOMAD, MINERvA and MiniBooNE experiments. The present theoretical approach gives an excellent description of differential cross section data. The calculations with axial mass M_{A} = 0.979 and 1.05 GeV are compatible with data from most of the experiments.
The integral measurement of the $^{12}$C(n,p)$^{12}$B reaction was performed at the neutron time of flight facility n_TOF at CERN. The total number of $^{12}$B nuclei produced per neutron pulse of the n_TOF beam was determined using the activation technique in combination with a time of flight technique. The cross section is integrated over the n_TOF neutron energy spectrum from reaction threshold at 13.6 MeV to 10 GeV. Having been measured up to 1 GeV on basis of the $^{235}$U(n,f) reaction, the neutron energy spectrum above 200 MeV has been reevaluated due to the recent extension of the cross section reference for this particular reaction, which is otherwise considered a standard up to 200 MeV. The results from the dedicated GEANT4 simulations have been used to evaluate the neutron flux from 1 GeV up to 10 GeV. The experimental results related to the $^{12}$C(n,p)$^{12}$B reaction are compared with the evaluated cross sections from major libraries and with the predictions of different GEANT4 models, which mostly underestimate the $^{12}$B production. On the contrary, a good reproduction of the integral cross section derived from measurements is obtained with TALYS-1.6 calculations, with optimized parameters.
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