Speaker
Description
Two particle transfer reactions provide realistic tools to understand reaction mechanisms due to
the enhanced matrix elements connecting systems of neighbouring nuclei differing by two units. The
resultant pairing interactions in the (A+2) nuclei, if present in a weakly bound system near the drip
lines, can develop diffused Borromean halos as the Cooper pair of the nucleons can scatter into the
continuum states of the intermediary nucleus [1]. The $^6$He nucleus presents a perfect candidate to
study such pairing effects in a diffused halo near the neutron drip line. In fact, apart from the nuclear
physics viewpoint, an understanding of 6He structure is also crucial due to its vital role in stellar
astrophysics [2].
We, therefore, perform two neutron transfer calculations for the reaction $^{18}$O($^4$He,$^6$He)$^{16}$O using a
modified version of the Transformed Form Factors (TFF) code [3]. We generate the spectra of the
intermediary $^5$He via the pseudostates (PS) approach, for which we use the analytical transformed
harmonic oscillator (THO) basis [4]. THO maintains the lucidity of the harmonic oscillator functions,
converting, however, their Gaussian asymptotic behavior to a better suited exponential mode [4]. We
differentiate three cases of interest on the basis of the ground state of $^5$He. In the two hypothetical
cases, it is bound with one neutron separation energies $S_n$ of 1 and 0.1 MeV. For the realistic case, a
state in our discretized continuum (at 0.69 MeV) represents the resonance at 0.79 MeV.
Our results indicate that pairing enhancement is largest for the continuum case and can significantly
enhance the two neutron transfer cross-sections in the cases when the intermediary nucleus does not
have a bound state. This provides a way to study the formation of Borromean halos near the neutron
drip line in the light mass region.
References
[1] W. von Oertzen and A. Vitturi, Reports on Progress in Physics 64, 1247 (2001).
[2] A. Bartlett, J. G orres, G. J. Mathews, K. Otsuki, M. Wiescher, D. Frekers, A. Mengoni, and J.
Tostevin, Phys. Rev. C 74, 015802 (2006).
[3] L. Fortunato, I. Inci, J.-A. Lay, and A. Vitturi, Computation 5(3), 36 (2017).
[4] J. Casal, M. Rodr??guez-Gallardo, and J. M. Arias, Phys. Rev. C 88, 014327 (2013); J. A. Lay, A.
M. Moro, J. M. Arias, and J. G omez-Camacho, Phys. Rev. C 85, 054618 (2012).
| Topic | Theory |
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