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Register a new userStudy of $s$- and $d$-wave intruder strengths in $^{13}{rm B}_{rm g.s.}$ via a $p(^{13}{rm B},d)^{12}{rm B}$ reaction
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Experimental results of the $p(^{13}{rm B},d)^{12}{rm B}$ transfer reaction to the low-lying states in $^{12}$B are reported. The optical potential parameters for the entrance channel are extracted from the elastic scattering $p$($^{13}{rm B}$, $p$) measured in the same experiment, while those for the exit channel are global ones. Spectroscopic factors associated with the $p$-, $s$-, and $d$-wave neutron transfer to the known $^{12}$B states, are extracted by comparing the deuteron angular distributions with the calculation results. The separated $s$- and $d$-wave intruder strengths in $^{13}{rm B}_{rm g.s.}$ were determined to be $10(2)%$ and $6(1)%$, respectively, which follow roughly the systematics for the $N$ = 8 neutron-rich isotones. The measured total intruder strength is in good agreement with the shell model calculation, while the individual ones evolve quite differently. Particularly, the sudden change of the $d$-wave intensity between $^{13}$B and $^{12}$Be needs further theoretical interpretation.
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The astrophysical $^7{rm Be}(p, gamma)^8{rm B}$ direct capture process is studied in the framework of a two-body single-channel model with potentials of the Gaussian form. A modified potential is constructed to reproduce the new experimental value of the $S$-wave scattering length and the known astrophysical $S$ factor at the Gamow energy, extracted from the solar neutrino flux. The resulting potential is consistent with the theory developed by Baye [Phys. Rev. C {bf 62} (2000) 065803] according to which the $S$-wave scattering length and the astrophysical $S$ factor at zero energy divided by the square of ANC are related. The obtained results for the astrophysical $S$ factor at intermediate energies are in good agreement with the two data sets of Hammache {it et al.} [Phys. Rev. Lett. {bf 86}, 3985 (2001); {it ibid.} {bf 80}, 928 (1998)]. Linear extrapolation to zero energy yields $ S_{17}(0) approx (20.5 pm 0.5) , rm eV , b $, consistent with the Solar Fusion II estimate. The calculated reaction rates are substantially lower than the results of the NACRE II collaboration.
The parity-transfer $({}^{16}{rm O},{}^{16}{rm F}(0^-,{rm g.s.}))$ reaction is presented as a new probe for investigating isovector $0^-$ states in nuclei. The properties of $0^-$ states provide a stringent test of the threshold density for pion condensation in nuclear matter. Utilizing a $0^+ rightarrow 0^-$ transition in the projectile, the parity-transfer reaction transfers an internal parity to a target nucleus, resulting in a unique sensitivity to unnatural-parity states. Consequently, the selectivity for $0^-$ states is higher than in other reactions employed to date. The probe was applied to a study of the $0^-$ states in ${}^{12}{rm B}$ via the ${}^{12}{rm C}({}^{16}{rm O},{}^{16}{rm F}(0^-,{rm g.s.}))$ reaction at $247~{rm MeV/u}$. The excitation energy spectra were deduced by detecting the ${}^{15}{rm O}+p$ pair produced in the decay of the ${}^{16}{rm F}$ ejectile. A known $0^-$ state at $E_x = 9.3~{rm MeV}$ was observed with an unprecedentedly high signal-to-noise ratio. The data also revealed new candidates of $0^-$ states at $E_x=6.6 pm 0.4$ and $14.8 pm 0.3~{rm MeV}$. The results demonstrate the high efficiency of $0^-$ state detection by the parity-transfer reaction.
We investigate structure of $^{13}_Lambda{rm C}$ and discuss the difference and similarity between the structures of $^{12}{rm C}$ and $^{13}_Lambda{rm C}$ by answering the questions if the linear-chain and gaslike cluster states, which are proposed to appear in $^{12}{rm C}$, survives, or new structure states appear or not. We introduce a microscopic cluster model called, Hyper-Tohsaki-Horiuchi-Schuck-Ropke (H-THSR) wave function, which is an extended version of the THSR wave function so as to describe $Lambda$ hypernuclei. We obtained two bound states and two resonance (quasi-bound) states for $J^pi=0^+$ in $^{13}_Lambda{rm C}$, corresponding to the four $0^+$ states in $^{12}{rm C}$. However, the inversion of level ordering between the spectra of $^{12}{rm C}$ and $^{13}_Lambda{rm C}$, i.e. that the $0_3^+$ and $0_4^+$ states in $^{13}_Lambda{rm C}$ correspond to the $0_4^+$ and $0_3^+$ states in $^{12}{rm C}$, respectively, is shown to occur. The additional $Lambda$ particle reduces sizes of the $0_2^+$ and $0_3^+$ states in $^{13}_Lambda{rm C}$ very much, but the shrinkage of the $0_4^+$ state is only a half of the other states. In conclusion, the Hoyle state becomes quite a compact object with ${^{9}_Lambda{rm Be}}+alpha$ configuration in $^{13}_Lambda{rm C}$ and is no more gaslike state composed of the $3alpha$ clusters. Instead, the $0_4^+$ state in $^{13}_Lambda{rm C}$, coming from the $^{12}{rm C}(0_3^+)$ state, appears as a gaslike state composed of $alpha+alpha+^{5}_Lambda{rm He}$ configuration, i.e. the Hoyle analog state. A linear-chain state in a $Lambda$ hypernucleus is for the first time predicted to exist as the $0_3^+$ state in $^{13}_Lambda{rm C}$ with more shrunk arrangement of the $3alpha$ clusters along $z$-axis than the $3alpha$ linear-chain configuration realized in the $^{12}{rm C}(0_4^+)$ state.
A search for previously unobserved decays of beauty baryons to the final states $K^0_{rmscriptscriptstyle S} p pi^{-}$ and $K^0_{rmscriptscriptstyle S}p K^{-}$ is reported. The analysis is based on a data sample corresponding to an integrated luminosity of $1.0,$fb$^{-1}$ of $pp$ collisions. The $Lambda^0_{b} rightarrow overline{kern -0.2em K}^0_{rmscriptscriptstyle S}p pi^{-}$ decay is observed with a significance of $8.6,sigma$, with branching fraction begin{eqnarray*} {cal{B}}(Lambda^0_{b} rightarrow overline{kern -0.2em K}^0 p pi^{-}) & = & left(1.26 pm 0.19 pm 0.09 pm 0.34 pm 0.05 right) times 10^{-5} ,, end{eqnarray*} where the uncertainties are statistical, systematic, from the ratio of fragmentation fractions $f_{Lambda}/f_{d}$, and from the branching fraction of the $B^0 rightarrow K^0_{rmscriptscriptstyle S}pi^{+}pi^{-}$ normalisation channel, respectively. A first measurement is made of the $CP$ asymmetry, giving begin{eqnarray*} A_{C/!P} (Lambda^0_{b} rightarrow overline{kern -0.2em K}^0 p pi^{-}) & = & 0.22 pm 0.13mathrm{,(stat)} pm 0.03mathrm{,(syst)} , . end{eqnarray*} No significant signals are seen for $Lambda^0_{b} rightarrow K^0_{rmscriptscriptstyle S}p K^{-}$ decays, $Xi^{0}_{b}$ decays to both the $K^0_{rmscriptscriptstyle S}p pi^{-}$ and $K^0_{rmscriptscriptstyle S}p K^{-}$ final states, and the $Lambda^0_{b} rightarrow D^{-}_{s} (rightarrow K^0_{rmscriptscriptstyle S} K^{-}) p$ decay, and upper limits on their branching fractions are reported.
Differential cross sections and complete sets of polarization observables are presented for the Gamow-Teller $^{12}{rm C}(vec{p},vec{n})^{12}{rm N}({rm g.s.},1^+)$ reaction at a bombarding energy of 296 MeV with momentum transfers $q$ of 0.1 to $2.2{rm fm}^{-1}$. The polarization transfer observables are used to deduce the spin-longitudinal cross section, $ID_q$, and spin-transverse cross sections, $ID_p$ and $ID_n$. The data are compared with calculations based on the distorted wave impulse approximation (DWIA) using shell-model wave functions. Significant differences between the experimental and theoretical results are observed for all three spin-dependent $ID_i$ at momentum transfers of $q gtrsim 0.5{rm fm}^{-1}$, suggesting the existence of nuclear correlations beyond the shell model. We also performed DWIA calculations employing random phase approximation (RPA) response functions and found that the observed discrepancy is partly resolved by the pionic and rho-mesonic correlation effects.
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