Search

Using the reaction $^{7}$Li($^{7}$Li,$^{10}$C) we tried to populate states in the tetraneutron. A peak in the energy spectrum of identified $^{10}$C, which we cannot attribute to a reaction with any other of the target components, corresponds to an excitation of the $^{10}$C+4n system of 2.93±0.16 MeV. Under different kinematic conditions an equivalent peak was observed. For a binding energy of the tetraneutron of −2.93 MeV a much larger width than the observed upper limit of Γ<0.24 MeV (mainly due to experimental spread) is expected. Therefore, we favor the interpretation that this peak corresponds to $^{10}$C in the first excited state at 3.354 MeV and a tetraneutron with a binding energy of +0.42±0.16 MeV.

Nature 606(7915), 678 - 682 (2022). doi:10.1038/s41586-022-04827-6, Published by Nature Publ. Group, London [u.a.]

The SS-HORSE method is applied to describe the scattering of nucleons by light nuclei based on calculations within the No-Core Shell Model with JISP16 and Daejeon16 NN interactions. The resonant states in 5He, 5Li, and 7He nuclei have been investigated. The SS-HORSE method generalized to the case of the democratic decay is also applied to study a four-neutron system (tetraneutron). The calculations with JISP16 and Daejeon16 and with chiral NN interactions indicate the existence of a rather narrow low-energy tetraneutron resonance.

The tetraneutron has attracted the attention of nuclear physicists during the past decades, but there is still no unambiguous confirmation of its existence or non-existence. A new experiment based on $$^{8}$$ He(p, 2p) $$^{7}$$ H{t+ $$^{4}n$$ } reaction, with direct detection of the four neutrons, has been carried out at RIBF, which can hopefully help to draw a definite conclusion on the tetraneutron system.

7 pags., 3 figs. -- 27th International Nuclear Physics Conference (INPC2019), The tetraneutron has attracted the attention of nuclear physicists during the past decades, but there is still no unambiguous confirmation of its existence or nonexistence. A new experiment based on 8 He(p,2p)7H{t+4n} reaction, with direct detection of the four neutrons, has been carried out at RIBF, which can hopefully help to draw a definite conclusion on the tetraneutron system., We acknowledge the support of the RIBF accelerator staff and the BigRIPS team for providing the high-quality beam. Z. H. Yang acknowledges the financial support from the Foreign Postdoctoral Researcher program of RIKEN. T. Aumann acknowledges the support by DFG via SFB 1245. P. Koseoglou acknowledges the support from BMBF (NUSTAR.DA grant No.05P 15RDFN1).

The existence of multi-neutron systems has always been a debatable question. Indeed, both inter-nucleon correlations and a large continuum coupling occur in these states. We then employ the ab-initio no-core Gamow shell model to calculate the resonant energies and widths of the trineutron and tetraneutron systems with realistic interactions. Our results indicate that trineutron and tetraneutron are both unbound and bear broad widths. The calculated energy and width of tetraneutron are also comparable with recent experimental data. Moreover, our calculations suggest that the energy of trineutron is lower than that of tetraneutron, while its resonance width is also narrower. This strongly suggests that trineutron is more likely to be experimentally observed than tetraneutron. We thus suggest experimentalists to search for trineutron at low energy., 5 pages; 2 figures

Currently, neutron matter and neutron stars as subjects of research are firmly established in physics and astrophysics. It is logical to consider their chemical properties, based on the principles of general chemistry. The paper shows how neutron matter is formed; besides gravitational neutronization, other mechanisms, such as condensation of ultracold neutrons (UCN) and neutronization by critically increasing the sequence number of elements in the Periodic System (PS) are considered. Thus, arises the question of a possible “end” of the PS. Proceeding from the initial D.I. Mendeleev’s premise concerning his PS, the neutron matter must inevitably be placed in a group of rare gases and at the “beginning” of the System. The possibility of a chemical interaction of UCN with the substances with an odd number of electrons is also considered. A planned experiment to study the chemical properties of UCN is discussed. We offer to expand PS beyond classical chemical substances and use it to cover much wider universe matter, based on the forgotten ideas of D.I. Mendeleev. As a result, neutron and its isotopes (dineutron, tetraneutron, etc.) will begin and the neutron star matter will end the PS.

Background: Several previous studies provided contradicting results for the four-neutron system, some claiming the existence of a 0+ near-threshold resonance, others denying presence of any observable resonant states. Purpose: Since most of the studies employed enhanced two-neutron interactions to follow the evolution of an artificially bound state into a continuum one, we examine several enhancement schemes that produce a bound dineutron as well. Methods: We study the four-neutron system by solving exact four-particle equations. By varying the interaction enhancement factor we calculate two-dineutron scattering phase shifts and cross sections. Results: When the same enhancement factor is used in all partial waves, a bound tetraneutron emerges together with a strongly bound dineutron. Furthermore, such a 0+ tetraneutron evolves not into a resonance but into a virtual state. Weak enhancement of S waves together with strongly enhanced higher waves is needed for the emergence of the resonant state. Anyhow the resonant behavior disappears well before reaching the physical interaction strength. Conclusions: The interaction enhancement scheme using the same factor for all waves, employed in several previous works, is misleading for the search of 0+ resonance as only a virtual state can emerge. Evolution of a bound tetraneutron into a resonance via an intermediate virtual state is possible with strong enhancement of higher two-neutron waves., Comment: 6 pages, 7 figures, to be published in Phys. Rev. C

International audience; A Comment on the Letter by S. Gandolfi, H.-W. Hammer, P. Klos, J. E. Lynn, and A. Schwenk, Phys. Rev. Lett. 118, 232501 (2017).PRLTAO0031-900710.1103/PhysRevLett.118.232501 The authors of the Letter offer a Reply.

In this work we investigate the possible condensation of tetraneutron resonant states in the lower density neutron rich gas regions inside Neutron Stars (NSs). Using a relativistic density functional approach we characterize the system containing different hadronic species including, besides tetraneutrons, nucleons and a set of light clusters ($^3$He, $\alpha$ particles, deuterium and tritium). $\sigma,\omega$ and $\rho$ mesonic fields provide the interaction in the nuclear system. We study how the tetraneutron presence could significantly impact the nucleon pairing fractions and the distribution of baryonic charge among species. For this we assume that they can be thermodynamically produced in an equilibrated medium and scan a range of coupling strengths to the mesonic fields from prescriptions based on isospin symmetry arguments. We find that tetraneutrons may appear over a range of densities belonging to the outer NS crust carrying a sizable amount of baryonic charge thus depleting the nucleon pairing fractions., Comment: 10 pages, 9 figures

A specific cluster approach, in the framework of the Isomorphic Shell Model, is employed to examine the possible stability of 2n, 4n, and 6n. According to this study 2n is definitely unstable, while 4n and 6n could be stable or, at least, exhibit a low-lying resonance. Better knowledge of the strength of the neutron-neutron force is highly desirable.

The tetraneutron has been drawing the attention of the nuclear physics community for decades, but a firm conclusion on its existence and properties is still far from being reached despite many experimental and theoretical efforts. New measurements have recently been performed at RIBF with the SAMURAI spectrometer by applying complementary reaction probes, which will help to pin down the properties of this four-neutron system., Comment: 5 pages, 2 figures, conference proceedings of XXII International Conference on Few-Body Problems in Physics (FB22), Caen, France, July 2018

The four-neutron system is studied using exact continuum equations for transition operators and solving them in the momentum-space framework. A resonant behavior is found for strongly enhanced interaction but not a the physical strength, indicating the absence of an observable tetraneutron resonance, in contrast to a number of earlier works. As the transition operators acquire large values at low energies, it is conjectured that this behavior may explain peaks in many-body reactions even without a resonance., 4+ pages, 3 figures, submitted to Phys.Lett.B

We continue the study of the tetraneutron resonance within the democratic SS-HORSE extension of the ab initio No-Core Shell Model using modern NN interactions. With Daejeon16 and SRG-evolved chiral Idaho N3LO NN interactions we obtain the S-matrix pole corresponding to the tetraneutron resonance with energy between 0.7 and 1.0 MeV and width between 1.1 and 1.7 MeV. However we do not obtain a low-lying narrow resonance with the original Idaho N3LO but, instead, we obtain a very low-lying virtual state with the energy of 15 keV.

International audience; The search for a resonant four-neutron system has been revived thanks to the recent experimental hints reported in Phys. Rev. Lett. 116, 052501 (2016). The existence of such a system would deeply impact our understanding of nuclear matter and requires a critical investigation. In this work, we study the existence of a four-neutron resonance in the quasi-stationary formalism using ab initio techniques with various two-body chiral interactions. We employ the No-Core Gamow Shell Model and the Density Matrix Renormalization Group method, both supplemented by the use of natural orbitals and a new identification technique for broad resonances. We demonstrate that while the energy of the four-neutron system may be compatible with the experimental value, its width must be larger than the reported upper limit, supporting the interpretation of the experimental observation as a reaction process too short to form a nucleus.

We present a summary of our recent publication concerning the derivation of the extended Casimir-Polder dispersive interaction between two neutrons. Dynamical polarizations of the neutrons, recently derived within Chiral Effective Theory are used for the purpose. An account of the higher frequency/energy behavior of these entities related to the opening of one-pion production channel and the excitation of the $\Delta$ resonance are taken into consideration in our derivation of the CP interaction. The neutron-neutron system in free space is treated in details so are the neutron-wall and the wall-neutron-wall systems. The case of tetraneutron (a 4 neutron system) in a resonant state is then briefly considered. The 4n CP interaction is evaluated to assess its potential relevance to the ongoing debate concerning the nature of the tetraneutron., Comment: Contribution to the 2nd Jagiellonian Symposium on Fundamental and Applied Subatomic Physics, June 4-9 , 2017, Krak\'ow. Submitted to Acta Physica Polonica B

International audience; This work is an attempt to model the 4n response function of a recent RIKEN experimental study of the double charge exchange 4He( 8He, 8Be) 4n 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 that destroys the neighboring nuclear chart. No other mechanisms, like cusps or related structures, were found.

We present quantum Monte Carlo calculations of few-neutron systems confined in external potentials based on local chiral interactions at next-to-next-to-leading order in chiral effective field theory. The energy and radial densities for these systems are calculated in different external Woods-Saxon potentials. We assume that their extrapolation to zero external-potential depth provides a quantitative estimate of three- and four-neutron resonances. The validity of this assumption is demonstrated by benchmarking with an exact diagonalization in the two-body case. We find that the extrapolated trineutron resonance, as well as the energy for shallow well depths, is lower than the tetraneutron resonance energy. This suggests that a three-neutron resonance exists below a four-neutron resonance in nature and is potentially measurable. To confirm that the relative ordering of three- and four-neutron resonances is not an artifact of the external confinement, we test that the odd-even staggering in the helium isotopic chain is reproduced within this approach. Finally, we discuss similarities between our results and ultracold Fermi gases., 6 pages, 5 figures, version compatible with published letter

Tetraneutron ($^4n$) has come back in the limelight, because of recent observation of a candidate resonant state at RIBF. We propose to investigate the pion double charge exchange (DCX) reaction, i.e. $^4\mathrm{He}({\pi}^- , {\pi}^+)$, as an alternative way to populate tetraneutron. An intense ${\pi}^-$ beam with the kinetic energy of ~850 MeV, much higher than that in past experiments at LAMPF and TRIUMF, will open up a possibility to improve the experimental sensitivity of the formation cross section, which will be much smaller than hitherto known DCX cross sections such as $^9\mathrm{Be}({\pi}^-, {\pi}^+)^9\mathrm{He}\ (g.s.)$., Comment: 4 pages, 1 figure; proceedings of the 14th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2016), Kyoto, Japan, 25-30 July 2016

We utilize various {\em ab initio} approaches to search for a low-lying resonance in the four-neutron ($4n$) system using the JISP16 realistic $NN$ interaction. Our most accurate prediction is obtained using a $J$-matrix extension of the No-Core Shell Model and suggests a $4n$ resonant state at an energy near $E_r = 0.8$ MeV with a width of approximately $\Gamma = 1.4$ MeV., Comment: 5 pages, 3 figures

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.

We theoretically investigate the possibility for a tetraneutron to exist as a low-energy resonance state. We explore a microscopic model based on the assumption that the tetraneutron can be treated as a compound system, where 3n + n and 2n + 2n coupled cluster configurations coexist. The influence of the Pauli principle on the kinetic energy of the relative motion of the neutron clusters is shown to result in their attraction. The strength of such attraction is high enough to ensure the existence of a low-energy resonance in the tetraneutron, provided that the oscillator length is large enough.

The influence of the Pauli exclusion principle on the relative motion of light neutron-rich nuclei in their collision is investigated within the microscopicmethod using as an example 11Be + n and 10Be + 2 n nuclear reactions, as well as 3 n + n and 2 n + 2 n reactions. Antisymmetrization effects related to the kinetic and potential energy of the relative motion of colliding nuclei are analyzed. The influence of the Pauli exclusion principle on the kinetic energy of the relative motion of the 11Be nucleus and a neutron is shown to result in their attraction. The same phenomenon is observed for the case of the 3 n + n cluster system. The strength of such attraction is high enough to ensure the existence of a bound state in the 12Be nucleus and a low-energy resonance in the tetraneutron. The conclusion is drawn that, for a resonance state in the 4 n system to exist, the value of the oscillator length must be large enough. It is shown also that increasing the oscillator length results in depression of the cluster-cluster potential.

Theoretical studies of broad states in the few-body systems beyond the neutron drip line have been performed. We introduce a theoretical model which allows to incorporate the initial structure of colliding nuclei, reaction mechanism, few-body effects and final-state interactions in studies of broad unbound states. The model is directly related to the sudden-removal approximation for high-energy knock-out or break-up reactions. We apply this model to qualitative studies of some general properties of broad few-body states including correlations for emitted fragments. The theoretical ideas are illustrated mainly using the example of 5H. The prospect for observation of broad continuum structures corresponding to the tetraneutron 4n is also discussed.

In light of a new experiment which claims a positive identification, we discuss the possible existence of the tetraneutron. We explore a novel model based on a dineutron-dineutron molecule. We show that this model is not able to explain the tetraneutron as a bound state, in agreement with other theoretical models already discussed in the literature., 9 pages, 3 figures, J. Phys. G, in press

Following recent work in which events which may correspond to a bound tetraneutron (4n) were observed, it is pointed out that from the theoretical perspective the two-body nucleon–nucleon (NN) force cannot by itself bind four neutrons, even if it could bind a dineutron. Unrealistic modifications of the NN force or introduction of unreaslistic four-nucleon force would be needed in order to bind the tetraneutron. The existence of other multineutron systems is discussed.

A system of four neutrons known as the tetraneutron is a hypothetical state in nuclear physics. The report of evidence for the fleeting existence of this state has implications for research into neutron stars.

We theoretically investigate the possibility for a tetraneutron to exist as a low-energy resonance state. We explore a microscopic model based on the assumption that the tetraneutron can be treated as a compound system where $^3$n+n and $^2$n+$^2$n coupled cluster configurations coexist. The influence of the Pauli principle on the kinetic energy of the relative motion of the neutron clusters is shown to result in their attraction. The strength of such attraction is high enough to ensure the existence of a low-energy resonance in the tetraneutron, provided that the oscillator length is large enough.

International audience; The t(6He,8He)p t(8He,10He)p reactions were studied in experiments with 25A MeV 6He beam and 27.4A MeV 8He beams and an unique tritium gas target. Results on the 8He and 10He excitation energy spectra are presented. The 8He spectrum exhibits 3 states, apart of the ground state and known (2+) state at 3.6 MeV, the third state is seen at 5.4 MeV. A tentative assignment 1+ is proposed for this structure. The 10He spectrum shows no event at the excitation energy below 3 MeV what is in contradiction with the earlier reports on this nucleus. A high statistics of α-n coincidence events collected for the 8He beam run has been subjected to analysis in order search for the bound tetraneutron. The search produced a negative result.

International audience

NESTER PTH, Détecteur MUST; International audience; Investigation of unbound nuclear systems 9He, 7H and 4n was performed at GANIL-SPIRAL using the 8He beam at 15.3 A MeV and a CD2 target. The missing mass spectra were deduced from kinetic energies and emission angles of light ejectiles detected by the Silicon array MUST. In addition to previously known low-lying narrow resonant states in 9He, the d(8He,p) reaction displays a structure just above neutron emission threshold, identified with the “true” ground state of 9He. The analysis of angular distributions shows that the inversion of s1/2 and p1/2 neutron shells previously observed in 11Be and 10Li also exists in the lightest N=7 isotone 9He. The d(8He,3He) and d(8He,6Li) reactions were used to search for resonant states in the t+4n (7H) and 4n systems, respectively. The missing mass spectrum of the 4n system does not give evidence for the existence of a bound “tetraneutron”. However the comparison with the results of 5-body phase-space calculations emphasizes the existence of correlations in the 4n system. The broad structure observed at ~=2 MeV above the t+4n emission threshold is proposed to be the ground state of 7H

Theoretical calculations as well as previous experimental results from fission, spallation and double charge exchange reactions have concluded against the existence of bound multineutron clusters. The recent availability of intense neutron-rich RNB provides the opportunity to reinvestigate this long-standing problem in a highly selective way. The 8He(d,6Li)4n reaction at 15.8 MeV/A incident energy was studied two times at GANIL-SPIRAL in order to investigate the eventual existence of bound or resonant states in the four neutron system (Tetraneutron). The 4n missing mas spectrum was deduced from kinetic energies and emission angles of 6Li ejectiles, measured by the Silicon array MUST. Neutrons emitted in coïncidence were also detected in Plastic detectors. A resonant-like structure was observed in 2002 experiment at ~2.5 MeV above 4n threshold but its identification was not confirmed in the 2004 experiment. Anyway, results show a strong correlation between the four neutrons emitted., L'existence éventuelle de multineutrons liés, suggérée par de récents résultats expérimentaux serait susceptible de remettre radicalement en cause bien des certitudes établies sur l'interaction nucléon-nucléon. Nous avons choisi d'utiliser la réaction 8He(d,6Li) pour mesurer le spectre d'énergie du système 4n afin d'y rechercher la présence d'un pic signant l'existence éventuelle d'un noyau lié neutre : le « Tetraneutron », ou bien celle d'un état résonant à basse énergie d'excitation. Cette étude a été menée au GANIL en utilisant le faisceau secondaire de 8He de 15.8 A.MeV fourni par SPIRAL. L'ensemble de détecteurs Silicium à pistes MUST a été utilisé pour mesurer les angles d'émission et les énergies des 6Li, et en déduire la masse manquante du système des quatre neutrons. Une nouvelle expérience réalisée en 2004 avec une statistique plus élevée et une meilleure détermination du fond n'a pas permis de confirmer l'existence de la structure étroite observée en 2002 à une énergie d'environ 2.5 MeV .L'analyse des résultats démontre cependant la présence de fortes corrélations entre les quatre neutrons émis.

10 pages, 6 figs, 2 tables. To be published in Phys. Rev. C; The possible existence of four-neutron resonances close to the physical energy region is explored. Faddeev-Yakubovsky equations have been solved in configuration space using realistic nucleon-nucleon interaction models. Complex scaling and analytical continuation in the coupling constant methods were used to follow the resonance pole trajectories, which emerge out of artificially bound tetraneutron states. The final pole positions for four-neutron states lie in the third energy quadrant with negative real energy parts and should thus not be physically observable.

Various aspects of the application of shell model approaches to cluster transfer reactions involving exotic nuclei are discussed. A scheme to calculate Spectroscopic Amplitudes for transfer reactions is given. It is calculated for a tetraneutron in 8He as an example. The reduction of the t+t clustering in the 6He nucleus, suggested by an experiment where transfer reactions were studied in the 6He+p collision is confronted with the concept of a supermultiplet for A=6 nuclei.

We analyze the elastic scattering of protons on a 4n system. This was used as part of the detection technique of a recent experiment [1] to search for the 4n (tetraneutron) as a bound particle. We show that it is unlikely that this process alone could yield the events reported in ref. [1], unless the 4n has an anomalously large backward elastic scattering amplitude., Comment: 6 pages, 2 figures, accepted for publication in Phys. Rev. C

10 pages, 2 tables, 13 figures.--PACS nrs.: 21.45.1v, 25.10.1s, 21.10.Gv.--ArXiv pre-print available at: http://arxiv.org/abs/nucl-ex/0111001, A new approach to the production and detection of bound neutron clusters is presented. The technique is based on the breakup of beams of very neutron-rich nuclei and the subsequent detection of the recoiling proton in a liquid scintillator. The method has been tested in the breakup of intermediate energy (30-50 MeV/nucleon) Li-11, Be-14, and B-15 beams. Some six events were observed that exhibit the characteristics of a multineutron cluster liberated in the breakup of Be-14, most probably in the channel Be-10+(4)n. The various backgrounds that may mimic such a signal are discussed in detail., This work was funded under the auspices of the IN2P3-CNRS (France) and EPSRC (United Kingdom). Additional support from the ALLIANCE program (Ministère des Affaires Etrangères and British Council) and the Human Capital and Mobility Program of the European Community (Contract No. CHGE-CT94-0056) is also acknowledged.

The tetraneutron state is studied in the framework of the chiral quark model with tetrahedron configuration. The universal attraction property of σ-meson exchange leads to a strong attraction in the effective potential of the system. It is possible to form a bound state. For comparison, the naive quark model is also employed to carry out the calculation. A weak attraction, which is too weak to bind the system, is obtained.

The trineutron and tetraneutron binding energies are calculated using an interaction which reproduces 3H, 3He, 4H, 4He, and 4Li ground-state properties. A 4ħω model space and completely symmetrized translationally invariant harmonic oscillator eigenstates are used in the analysis. The calculation yields a 3n eigenvalue within the range suggested in an experiment by Ohlsen et al. The 4n eigenvalue is consistent with the location of the first T = 2 level in the 4He system.

The present search for tetraneutrons (4n) in (3He +Te) interactions yields negative results. The formation probability (F) of a tetraneutron per 4 neutrons is determined to be smaller than 1.5 × 10−7 if the 4n half-life (t 1 2 ) is assumed to be longer than 10−9 s. If t 1 2 −9 s, quantities t 1 2 and F depend upon each other according to the relation Ft 1 2 −16 s . The upper limits for the average (3He, 4n) cross section are 28 and 19 μb at 44 and 130 MeV bombarding energies, respectively. These limits are two orders of magnitude lower than a recently reported positive value.

The momentum spectrum for double-charge-exchange of π − on 4 He has been measured at 0° and T π − = 165 MeV. A 1σ upper limit of 22 nb/sr is set on the cross section for transitions leading to bound tetraneutrons. The cross section in the continuum region is shown to be inconsistent with a four-neutron phase space distribution, while a model including final state interaction effects gives better agreement with experiment.

A search for the existence of the tetraneutron has been made using the double charge exchange reaction π − + 208 Pb → 4 n + π + + residuals for 4n production and the capture process in the same target, 208 Pb + 4 n → 212 Pb + γ , for the 4n detection. No event has been found, giving an upper limit for the product of the production cross section σp, the detection cross section σd and the 4n lifetime τ. Assuming 10−18 ≦ τ ≦ 10−9 sec it follows that σpσdτ ≦ 2.5 × 10−65cm4 sec with 90 % confidence, and for τ ≧ 10 −9 sec , σ p σ d ≦ 2.5 × 10 −56 cm 4 with 90 % confidence. The magnitude of this value is comparable to the experimental limit of the 4He(π−, π+)4n cross section.