Tue·Aug 15, 2017Tuesday·August 15, 2017

1. 01*

   Theoretical investigation of two-particle two-hole effect on spin-isospin excitations through charge-exchange reactions

   Tokuro Fukui🇯🇵 · Futoshi Minato🇯🇵

   Coherent one-particle one-hole (1p1h) excitations have given us effective insights into general nuclear excitations. However, the two-particle two-hole (2p2h) excitation beyond 1p1h is now recognized as critical for the proper description of experimental data of various nuclear responses. The spin-flip charge-exchange reactions ${}^{48}\mathrm{Ca}(p,n{)}^{48}\mathrm{Sc}$ are investigated to clarify the role of the 2p2h effect on their cross sections. The Fermi transition of ${}^{48}\mathrm{Ca}$ via the $(p,n)$ reaction is also investigated in order to demonstrate our framework. The transition density is calculated microscopically with the second Tamm-Dancoff approximation, and the distorted-wave Born approximation is employed to describe the reaction process. A phenomenological one-range Gaussian interaction is used to prepare the form factor. For the Fermi transition, our approach describes the experimental behavior of the cross section better than the Lane model, which is the conventional method. For spin-flip excitations including the GT transition, the 2p2h effect decreases the magnitude of the cross section and does not change the shape of the angular distribution. The $\Delta l=2$ transition of the present reaction is found to play a negligible role. The 2p2h effect will not change the angular-distributed cross section of spin-flip responses. This is because the transition density of the Gamow-Teller response, the leading contribution to the cross section, is not significantly varied by the 2p2h effect.

   ↳ nucl-thnucl-exPRC(2017)·4 citations
2. 02*

   Models, measurements, and effective field theory: proton capture on Beryllium-7 at next-to-leading order

   Xilin Zhang🇺🇸 · Kenneth M. Nollett🇺🇸 · Daniel R. Phillips🇺🇸

   We employ an effective field theory (EFT) that exploits the separation of scales in the p-wave halo nucleus ${}^8\mathrm{B}$ to describe the process ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ up to a center-of-mass energy of 500 keV. The calculation, for which we develop the lagrangian and power counting, is carried out up to next-to-leading order (NLO) in the EFT expansion. The power counting we adopt implies that Coulomb interactions must be included to all orders in ${\alpha }_{\mathrm{em}}$. We do this via EFT Feynman diagrams computed in time-ordered perturbation theory, and so recover existing quantum-mechanical technology such as the two-potential formalism for the treatment of the Coulomb-nuclear interference. Meanwhile the strong interactions and the E1 operator are dealt with via EFT expansions in powers of momenta, with a breakdown scale set by the size of the ${}^7$Be core, $\Lambda \approx 70$ MeV. Up to NLO the relevant physics in the different channels that enter the radiative capture reaction is encoded in ten different EFT couplings. The result is a model-independent parametrization for the reaction amplitude in the energy regime of interest. To show the connection to previous results we fix the EFT couplings using results from a number of potential model and microscopic calculations in the literature. Each of these models corresponds to a particular point in the space of EFTs. The EFT structure therefore provides a very general way to quantify the model uncertainty in calculations of ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$. We also demonstrate that the only N${}^2$LO corrections in ${}^7\mathrm{Be}(p,\gamma {)}^8\mathrm{B}$ come from an inelasticity that is practically of N${}^3$LO size in the energy range of interest, and so the truncation error in our calculation is effectively N${}^3$LO. We also discuss the relation of our extrapolated $S(0)$ to the previous standard evaluation.

   ↳ nucl-thastro-ph.SRnucl-exPRC(2018)·19 citations
3. 03*

   Addendum: Muon-neutrino-induced charged current pion production

   U. Mosel🇩🇪 · K. Gallmeister🇩🇪

   This short paper is an addendum to a recent publication on charged current neutrino-induced pion production (Phys.\ Rev.\ C96 (2017) no.1, 015503). It presents comparisons of pion production cross sections measured at the T2K near detector for a CH target.

   ↳ nucl-thhep-exnucl-exPRC(2017)·31 citations
4. 04*

   Existence of inelastic supernumerary nuclear rainbow in ${}^{16}$O+${}^{12}$C scattering

   S. Ohkubo🇯🇵 · Y. Hirabayashi🇯🇵 · A. A. Ogloblin

   The existence of a supernumerary nuclear rainbow in inelastic scattering is reported. This is done by studying inelastic ${}^{16}$O scattering from ${}^{12}$C, exciting the $2^{+}$ (4.44 MeV) state of ${}^{12}$C and elastic scattering at the incident energies in the range 124 to 200 MeV, using the coupled channels method. An extended double folding potential is used. This is derived from realistic wave functions for ${}^{12}$C and ${}^{16}$O calculated with a microscopic $\alpha$ cluster model and a finite-range density-dependent nucleon-nucleon force. Excitations to the $2^{+}$ (4.44 MeV), 3${}^{-}$ (9.64 MeV) and $4^{+}$ (14.08 MeV) states of ${}^{12}$C, and the $3^{-}$ (6.13 MeV) and $2^{+}$ (6.92 MeV) states of ${}^{16}$O are included in the coupled channels calculations. The emergence of the supernumerary bow is understood by the properties of both the Luneburg-lens-like potential in the internal region and diffuse attraction in the outer region. The existence of a supernumerary rainbow for inelastic scattering in addition to the existence of a dynamically created secondary rainbow and a dynamically refracted primary rainbow for elastic scattering, which are not observed in meteorological rainbows, further deepens the understanding of nuclear rainbows.

   ↳ nucl-thnucl-exPRC(2017)·3 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.