Modelling double charge exchange response function for tetraneutron system

This work is an attempt to model the $4n$ response function of a recent RIKEN experimental study of the double charge exchange $^4$He($^8$He,$^8$Be)$^4$n reaction in order to put in evidence an eventual enhancement mechanism of the zero energy cross section, including a near-threshold resonance. This resonance can indeed be reproduced only by adding to the standard nuclear Hamiltonian an unphysically large T=3/2 attractive 3n-force which destroys the neighboring nuclear chart. No other mechanisms like cusps or related structures were found

Four- and Five-Body Scattering Calculations

We study the five-quark system $uudd{\bar s}$ in the standard non-relativistic quark model by solving the scattering problem. Using the Gaussian Expansion Method (GEM), we perform the almost precise multi-quark calculations by treating a very large five-body modelspace including the NK scattering channel explicitly. Although a lot of pseudostates (discretized continuum states) with $J^\pi={1/2}^\pm$ and $J^\pi={3/2}^\pm$ are obtained within the bound-state approximation, all the states in $1.4-1.85$ GeV in mass around ${\rm {\rm \Theta}}^+(1540)$ melt into non-resonant continuum states through the coupling with the NK scattering state in the realistic case, i.e., there is no five-quark resonance below 1.85GeV. Instead, we predict a five-quark resonance state of $J^\pi={1/2}^-$ with the mass of about 1.9GeV and the width of $\Gamma \simeq$ 2.68MeV. Similar calculation is done for the four-quark system $c{\bar c}q{\bar q}$ ($q=u,d$) in connection with X$^0$(3872)

Electric dipole moment of 13^{13}C

We calculate for the first time the electric dipole moment (EDM) of $^{13}$C generated by the isovector CP-odd pion exchange nuclear force in the $\alpha$-cluster model, which describes well the structures of low lying states of the $^{13}$C nucleus. The linear dependence of the EDM of $^{13}$C on the neutron EDM and the isovector CP-odd nuclear coupling is found to be $d_{^{13}{\rm C}} = -0.33 d_n - 0.0020 \bar G_\pi^{(1)}$. The linear enhancement factor of the CP-odd nuclear coupling is smaller than that of the deuteron, due to the difference of the structure between the $1/2^-_1$ state and the opposite parity ($1/2^+$) states. We clarify the role of the structure played in the enhancement of the EDM. This result provides good guiding principles to search for other nuclei with large enhancement factor. We also mention the role of the EDM of $^{13}$C in determining the new physics beyond the standard model.Comment: 11 pages, 4 figure