A candidate resonant tetraneutron state is found in the missing-mass spectrum obtained in the double-charge-exchange reaction ^{4}He(^{8}He,^{8}Be) at 186  MeV/u. The energy of the state is 0.83±0.65(stat)±1.25(syst)  MeV above the threshold of four-neutron decay with a significance level of 4.9σ. Utilizing the large positive Q value of the (^{8}He,^{8}Be) reaction, an almost recoilless condition of the four-neutron system was achieved so as to obtain a weakly interacting four-neutron system efficiently.

The effect of initial correlations between nucleons on the nuclear break-up mechanism is studied. A quantum transport theory which extends standard mean-field approach is developed to incorporate short range pairing correlation as well as direct nucleon-nucleon collisions. A time evolution of the nuclear break-up from a correlated system leading to the emission of two particles to the continuum is performed. We show that initial correlations have strong influence on relative angles between particles emitted in coincidence. The present qualitative study indicates that nuclear break-up might be a tool to infer the residual interaction between nucleons in the nuclear medium.PACS numbers: 21.60.Jz, 25.60.Je, 24.10.Cn Keywords: mean-field, correlations, nuclear reactions, nuclear break-up Nuclei are self-bound systems formed of fermions interacting through the strong nuclear interaction. While many facets of nuclei could be understood in term of independent particle motion, some aspects reveal internal correlations [1]. We consider here the so-called break-up process leading to the emission of nucleons to the continuum. Numerous dedicated models have been developed to account for this mechanism [2]. Among them, time dependent models based on the independent particle hypothesis have been shown to provide a good description of the nuclear as well as Coulomb break-up [3,4]. These approaches, by neglecting two-body correlations could however not provide appropriate theories when two nucleons are emitted from the same nucleus [5,6,7]. Interferometry measurements are being now analyzed using rather schematic models [7] and more elaborated theories. are highly desirable.The aim of the present work is twofold: (i) develop a microscopic quantum transport theory which incorporates effects beyond mean-field like pairing correlations and/or direct nucleon-nucleon scattering in the medium.(ii) present a qualitative study of nuclear break-up and show that this mechanism can be a tool of choice for the study of correlations in nuclei. Similar challenges to (i) are being now addressed in strongly correlated electronic systems using Time-Dependent Density Functional Theory (TDDFT) [8,9]. The Energy Density Functional (EDF) [10] shares many aspects with DFT and is expected to provide a universal treatment of static and dynamical properties of nuclei [10,11]. Current EDFs start from an effective interaction (of Skyrme or Gogny type) to provide an energy functional, denoted E(ρ), where ρ is the one-body density matrix. Then, guided by the Hamiltonian case, equations of motion are written in terms of the one-body density evolution given by i ∂ t ρ = [h [ρ], ρ], where h[ρ] ≡ ∂E(ρ)/∂ρ denotes the mean-field Hamiltonian. To account for the richness of phenomena in nuclear dynamics [12], different extensions of mean-field have been proposed starting from the evolution:where v c 12 denotes the effective vertex in the correlation channel, Tr 2 (.) is the partial trace on the second particle. C 12 denotes the two-body correlation defined from t...