Tetraneutron

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A tetraneutron is a hypothesised stable cluster of four neutrons. This cluster of particles is not supported by the current standard model of particle physics. However, there is some empirical evidence which suggests this particle does exist, based on an experiment by Francisco-Miguel Marqués and co-workers at the Ganil accelerator in Caen using a novel detection method in observations of the disintegration of beryllium and lithium nuclei.Template:Ref

This is a potentially significant discovery because nuclear theory suggests that these clusters should not be stable, and thus should not exist. Therefore, if the existence of stable tetraneutrons can be independently confirmed, considerable adjustments will have to be made to current nuclear models.Template:Ref. Bertulani and ZelevinskyTemplate:Ref proposed that, if it existed, the tetraneutron could be formed by a bound state of two dineutron molecules. This idea was further explored by Pieper Template:Ref label who showed that the existence of this 4-neutron molecule as a bound state, would require substantial modifications in the presently accepted form of the nucleon-nucleon interactions, and who concluded that it "does not seem possible to change modern nuclear Hamiltonians to bind a tetraneutron without destroying many other successful predictions of those Hamiltonians. This means that, should a recent experimental claim of a bound tetraneutron be confirmed, our understanding of nuclear forces will have to be significantly changed."

Contents 1 Marqués' experiment 2 Since Marqués' experiment 3 See also 4 External links 5 References

Marqués' experiment

As with many particle accelerator experiments, Marques' team fired atomic nuclei at one another and observed the 'spray' of particles from the resulting collisions. In this case the experiment involved firing beryllium-14, beryllium-15 and lithium-11 nuclei at a small carbon target. Their approach to the production and detection of bound neutron clusters was new and novel.Template:Ref label Current nuclear models suggest that four separate neutrons should result when beryllium-10 is produced, but the signal detected in the production of beryllium-10 suggested a multineutron cluster in the breakup products; most likely a beryllium-10 nucleus and four neutrons fused together into a tetraneutron.

Since Marqués' experiment

A later analysis of the detection method used in the Marques' experiment suggested that at least part of the original analysis was flawedTemplate:Ref, and attempts to reproduce these observations with different methods have not successfully detected any neutron clusters.Template:Ref Attempts to theoretically model interactions which might give rise to multineutron clusters have failed,Template:RefTemplate:RefTemplate:Ref and it:

"does not seem possible to change modern nuclear Hamiltonians to bind a tetraneutron without destroying many other successful predictions of those Hamiltonians. This means that, should a recent experimental claim of a bound tetraneutron be confirmed, our understanding of nuclear forces will have to be significantly changed."Template:Ref label

See also

• Neutron
• Free neutron
• Dineutron
• Neutronium

External links

• Announcement of possible tetraneutron observations

References

1. Template:NoteTemplate:Note labelF. M. Marqués et. al., Detection of neutron clusters, Phys. Rev. C 65, 044006 (2002)
2. Template:NoteTemplate:Note labelSteven C. Pieper, Can Modern Nuclear Hamiltonians Tolerate a Bound Tetraneutron?, Phys. Rev. Lett. 90, 252501 (2003)
3. Template:NoteC.A. Bertulani and V.G. Zelevinsky, Tetraneutron as a dineutron-dineutron molecule, J. Phys. G 29 (2003) 2431
4. Template:NoteB. M. Sherrill and C. A. Bertulani, Proton-tetraneutron elastic scattering, Phys. Rev. C 69, 027601 (2004)
5. Template:NoteD. V. Aleksandrov, et. al. Search for Resonances in the Three- and Four-Neutron Systems in the 7Li(7Li, 11C)3n and 7Li(7Li, 10C)4n Reactions, JETP Letters, 81, 43 (2005)
6. Template:NoteRimantas Lazauskas, and Jaume Carbonell, Three-neutron resonance trajectories for realistic interaction models, Phys. Rev. C 71, 044004 (2005)
7. Template:NoteKoji Arai, Resonance states of 5H and 5Be in a microscopic three-cluster model, Phys. Rev. C 68, 034303 (2003)
8. Template:NoteA. Hemmdan, W. Glöckle, and H. Kamada, Indications for the nonexistence of three-neutron resonances near the physical region, Phys. Rev. C 66, 054001 (2002)