Di-neutron and the three-nucleon continuum observables

Abstract

We investigate how strong a hypothetical 1 S 0 bound state of two neutrons would affect different observables in the neutron-deuteron reactions. To that aim we extend our momentum space scheme of solving threenucleon Faddeev equations to incorporate in addition to the deuteron also the 1 S 0 dineutron bound state.We discuss effects induced by dineutron on the angular distribution of the neutron-deuteron elastic scattering and cross sections of the deuteron breakup. A comparison to the available data for neutron-deuteron total cross sections and elastic scattering angular distributions cannot decisively exclude a possibility that the two neutrons can form 1 S 0 bound state. However, the strong modifications of a final-state-interaction peak of the neutron-deuteron breakup when changing from negative to positive values of the neutron-neutron scattering length seems to exclude existence of dineutron.

A Method for Unambiguous Detection of a Hypothetical Bound Two-Neutron System

“…It is possible to extend the proposed scheme on searches for heavier neutral nuclei ( 3 n, 4 n) exploiting the π − absorption at rest on 4 He and, in further perspective, on lithium isotopes.…”

“…Three-nucleon forces cannot account for these discrepancies. Increasing the binding of the (standard) nn potential partly improves the situation but the results are inconclusive yet [4]. (iv) An interesting hint for the stronger than commonly accepted nn binding comes from lattice QCD calculations [8].…”

“…They differ also in the detection of a multi-neutron bound state. The strategy of the first experiment [12] is to produce a highly (charge) depleted system in the double pion exchange reaction (DPE) on helium: 4 He(π − , π + ) 4 n and looking for possible structures in the spectrum of the recoiling pion. The second experiment [13] tries to produce bound tetra-neutrons by breaking up neutron reach, loosely bound 14 Be nuclei in the Coulomb field and subsequently detecting neutral particles in a liquid organic scintillator.…”

“…As all these arguments give only limited confidence (see e.g. [4]), the nonexistence of bound di-neutrons is still an open question.…”

Calculations of Three-Nucleon Reactions

“…The large stability of the QFS cross sections to the underlying dynamics, implies that the present day 1 S 0 nn interaction is probably incorrect. Modifications of the 1 S 0 nn force by multiplying its matrix elements by a factor λ lead to large changes of the nn QFS cross sections, leaving the np ones practically unchanged [10][11][12]. To remove the discrepancy found in experiment for nn QFS one needs to increase λ by about 8 %.…”