Neutrino-nucleus reactions on ${}^{16}\mathrm{O}$ based on new shell-model Hamiltonians

Neutrino-induced reactions on ${}^{16}\mathrm{O}$ are investigated by shell-model calculations with new shell-model Hamiltonians, which can describe well the structure of $p$-shell and $p-sd$-shell nuclei. The distribution of the spin-dipole strengths in ${}^{16}\mathrm{O}$, which give major contributions to the $\nu -{}^{16}\mathrm{O}$ reaction cross sections, is studied with the new Hamiltonians. Muon-capture reaction rates on ${}^{16}\mathrm{O}$ are also studied to discuss the quenching of the axial-vector coupling in the nuclear medium. Charged-current and neutral-current reaction cross sections are evaluated in various particle and $\gamma$ emission channels as well as the total ones at neutrino energies up to $E_{\nu }\approx 100$ MeV. Branching ratios for the various channels are obtained by the Hauser-Feshbach statistical model calculations, and partial cross sections for single- and multiparticle emission channels are evaluated. The cross sections updated are compared with previous continuum random phase approximation calculations. Effects of multiparticle emission channels on nucleosynthesis in core-collapse supernova explosions are investigated. Inclusion of $\alpha p$ emission channels is found to lead to an enhancement of production yields of ${}^{11}\mathrm{B}$ and ${}^{11}\mathrm{C}$ through ${}^{16}\mathrm{O}(\nu ,{\nu }^{\prime }\alpha p){}^{11}\mathrm{B}$ and ${}^{16}\mathrm{O}({\nu }_e,e^{-}\alpha p){}^{11}\mathrm{C}$ reactions, respectively.

Figure 1

(a) Spin-dipole strengths for ${}^{16}\mathrm{O}\to {}^{16}\mathrm{F}$ obtained by shell-model calculations with SFO-tls. $E_x$ denotes the excitation energy of ${}^{16}\mathrm{F}$. (b) Comparison of the spin-dipole strengths for ${}^{16}\mathrm{O}\to {}^{16}\mathrm{F}$ obtained with SFO-tls and those with SFO. The strengths are folded over a Lorentzian with a width of 1 MeV. $E_x$ denotes the excitation energy of ${}^{16}\mathrm{O}$.

Figure 2

Total reaction cross sections for (a) ${}^{16}\mathrm{O}({\nu }_e,e^{-}){}^{16}\mathrm{F}$, (b) ${}^{16}\mathrm{O}({\overline{\nu }}_e,e^{+}){}^{16}\mathrm{N}$, and (c) ${}^{16}\mathrm{O}(\nu ,{\nu }^{\prime }){}^{16}\mathrm{O}$ obtained by shell-model calculations with the SFO-tls and SFO as well as those of the CRPA calculation [17].

Figure 3

Contributions from each $0^{-}, 1^{-}$, and $2^{-}$ multipoles as well as the total cross sections for ${}^{16}\mathrm{O}({\nu }_e,e^{-}){}^{16}\mathrm{F}$ as a function of excitation energy $E_x$ at (a) $E_{\nu }=30$ MeV and (b) $E_{\nu }=50$ MeV. The cross sections are folded over a Lorentzian with a width of 1 MeV.

Figure 4

The same as Fig. 3 for ${}^{16}\mathrm{O}({\overline{\nu }}_e,e^{+}){}^{16}\mathrm{N}$.

Figure 5

The same as Fig. 3 for ${}^{16}\mathrm{O}(\nu ,{\nu }^{\prime }){}^{16}\mathrm{O}$. Contributions from the $1^{+}$ multipole are also shown.

Figure 6

Partial cross sections to various channels of ${}^{16}\mathrm{O}({\nu }_e,e^{-}X)$ as function of neutrino energy $E_{\nu }$. (a) Cases for $X=p, d$ and $pn$, and $pp$ as well as the total cross section are shown. (b) Cases for $X={}^3\mathrm{He}$ (and $dp, ppn$), $\alpha , {}^3\mathrm{He}p$, and $\alpha p$ are shown.

Figure 7

The same as Fig. 6 for ${}^{16}\mathrm{O}({\overline{\nu }}_e,e^{+}X)$. (a) Cases for $X=n, d$, and $pn$, and the transition to ${}^{16}\mathrm{N}_{g.s.}$ as well as the total cross section. (b) Cases for $X={}^3\mathrm{H}$ (and $dn, pnn$), $\alpha , \alpha n$, and $nn$ are shown.

Figure 8

The same as Fig. 6 for ${}^{16}\mathrm{O}(\nu ,{\nu }^{\prime }X)$. (a) Cases for $X=n, p, d$ and $pn$, and $pp$ as well as the total cross section. (b) Cases for $X={}^3\mathrm{H}$ (and $dn, pnn$), ${}^3\mathrm{He}$ (and $dp, ppn$), $\alpha , \alpha n, \alpha p$, and $\gamma$ are shown.

Figure 9

Partial cross sections for ${}^{16}\mathrm{O}({\nu }_e,e^{-}X)$ for each multipole (a) $0^{-}$, (b) $1^{-}$, and $2^{-}$ as function of $E_x$ for $E_{\nu }=50$ MeV. Cases for $X=p, pp, {}^3\mathrm{He}, \alpha$, and $\alpha p$ as well as the total cross section are shown.

Figure 10

The same as Fig. 9 for ${}^{16}\mathrm{O}({\overline{\nu }}_e,e^{+}X)$. Cases for $X=n, d$ or $pn, \alpha , {}^3\mathrm{H}, \alpha p$, and the transition to ${}^{16}\mathrm{O}_{g.s.}$ are shown.

Figure 11

The same as Fig. 10 for ${}^{16}\mathrm{O}(\nu ,{\nu }^{\prime }X)$. Cases for $X=n, p, \alpha , \alpha p$, and $\gamma$ are shown.

Figure 12

Mass fraction distributions of (a) main elements, (b) ${}^{11}\mathrm{B}$, (c) ${}^{11}\mathrm{C}$, and (d) ${}^6\mathrm{Li}, {}^7\mathrm{Li}, {}^7\mathrm{Be},{}^9\mathrm{Be}$, and ${}^{10}\mathrm{B}$ for a model with $M=15M_{\odot }$. The horizontal axis denotes the cumulative mass of the star from the center in the solar mass unit $M_{\odot }$. Short-dashed, long-dashed, and solid curves in (b) and (c) are for cases 1, 2, and 3, respectively (see text). Curves in (d) are for case 3.

Figure 13

The same as Fig. 12 for $M=20M_{\odot }$.