# Physics:Hexaquark

Short description: Hypothetical particles made up of six quarks or antiquarks

In particle physics hexaquarks, alternatively known as sexaquarks,[1] are a large family of hypothetical particles, each particle consisting of six quarks or antiquarks of any flavours. Six constituent quarks in any of several combinations could yield a colour charge of zero; for example a hexaquark might contain either six quarks, resembling two baryons bound together (a dibaryon), or three quarks and three antiquarks.[2] Once formed, dibaryons are predicted to be fairly stable by the standards of particle physics.

A number of experiments have been suggested to detect dibaryon decays and interactions. In the 1990s, several candidate dibaryon decays were observed but they were not confirmed.[3][4][5]

There is a theory that strange particles such as hyperons[6] and dibaryons[7] could form in the interior of a neutron star, changing its mass–radius ratio in ways that might be detectable. Accordingly, measurements of neutron stars could set constraints on possible dibaryon properties.[8] A large fraction of the neutrons in a neutron star could turn into hyperons and merge into dibaryons during the early part of its collapse into a black hole . These dibaryons would very quickly dissolve into quark–gluon plasma during the collapse, or go into some currently unknown state of matter.

## D-star hexaquark

In 2014, a potential dibaryon was detected at the Jülich Research Center at about 2380 MeV. The center claimed that the measurements confirm results from 2011, via a more replicable method.[9][10] The particle existed for 10−23 seconds and was named d*(2380).[11] This particle is hypothesized to consist of three up and three down quarks, and has been proposed as a candidate for dark matter.[12][13][14]

It is theorized that groups of d-star particles could form Bose–Einstein condensates due to prevailing low temperatures in the early universe, a state in which they overlap and blend together, a bit like the protons and neutrons inside atoms. Under the right conditions, BECs made of hexaquarks with trapped electrons could behave like dark matter.[15] According to the researchers, this result indicates that during the earliest moments after the Big Bang, as the cosmos slowly cooled, stable d*(2830) hexaquarks could have formed alongside baryonic matter, and the production rate of this particle would have been sufficient to account for the 85% of the Universe's mass that is believed to be Dark Matter.[16]

Critics say that even if it is possible to create a d* condensate as proposed, it cannot survive the intense radiation of the early Universe. Once they are blasted apart, there is no way to create more d* particles capable of forming a Bose-Einstein condensate, as the conditions that admit their creation will have passed.[17]

## H dibaryon

In 1977, Robert Jaffe proposed that a possibly stable H dibaryon with the quark composition udsuds could notionally result from the combination of two uds hyperons.[18] Calculations have shown that this particle is light and (meta)stable. It actually takes more than twice the age of the universe to decay. Data constrains the existence of such a particle, and it turns out that it is still allowed.[1][19][20][21][22][23] As per one analysis, a hypothetical SU(3) flavor-singlet, highly symmetric, deeply bound neutral scalar hexaquark S=uuddss, which due to its features has escaped from experimental detection so far, may be considered as a candidate for a baryonic dark matter. However, existence of this state may contradict the stability of oxygen nuclei, necessitating further thorough analysis of it.[24]

## Others

• In 2022 Riken researchers studied the existence of triply charmed dibaryon $\displaystyle{ \Omega_{ccc}\Omega_{ccc} }$ concluding computationally that it should fall within a feasible regime.[25][26]

## References

1. Vijande, J.; Valcarce, A.; Richard, J.-M. (2011). "Stability of hexaquarks in the string limit of confinement". Physical Review D 85 (1): 014019. doi:10.1103/PhysRevD.85.014019. Bibcode2012PhRvD..85a4019V.
2. Belz, J. (1996). "Search for the weak decay of an H dibaryon". Physical Review Letters 76 (18): 3277–3280. doi:10.1103/PhysRevLett.76.3277. PMID 10060926. Bibcode1996PhRvL..76.3277B.
3. Stotzer, R. W. (1997). "Search for H dibaryon in 3He (K, K+) Hn". Physical Review Letters 78 (19): 3646–36490. doi:10.1103/PhysRevLett.78.3646. Bibcode1997PhRvL..78.3646S.
4. Alavi-Harati, A. (2000). "Search for the weak decay of a lightly bound H0 dibaryon". Physical Review Letters 84 (12): 2593–2597. doi:10.1103/PhysRevLett.84.2593. PMID 11017277. Bibcode2000PhRvL..84.2593A.
5. Ambartsumyan, V. A.; Saakyan, G. S. (1960). "The Degenerate Superdense Gas of Elementary Particles". Soviet Astronomy 37: 193. Bibcode1960SvA.....4..187A.
6. Kagiyama, S.; Nakamura, A.; Omodaka, T. (1992). "Compressible bag model and dibaryon stars". Zeitschrift für Physik C 56 (4): 557–560. doi:10.1007/BF01474728. Bibcode1992ZPhyC..56..557K.
7. Faessler, A.; Buchmann, A. J.; Krivoruchenko, M. I. (1997). "Constraints to coupling constants of the ω- and σ-mesons with dibaryons". Physical Review C 56 (3): 1576–1581. doi:10.1103/PhysRevC.56.1576. Bibcode1997PhRvC..56.1576F.
8. Adlarson, P. (2014). "Evidence for a New Resonance from Polarized Neutron-Proton Scattering". Physical Review Letters 112 (2): 202301. doi:10.1103/PhysRevLett.112.202301. Bibcode2014PhRvL.112t2301A.
9. Bashkanov, M. (2020). "A new possibility for light-quark dark matter". Journal of Physics G 47 (3): 03LT01. doi:10.1088/1361-6471/ab67e8. Bibcode2020JPhG...47cLT01B.
10. Jaffe, R. L. (1977). "Perhaps a Stable Dihyperon?". Physical Review Letters 38 (5): 195–198. doi:10.1103/PhysRevLett.38.195. Bibcode1977PhRvL..38..195J.
11. Farrar, G. R. (2017). "Stable Sexaquark". arXiv:1708.08951 [hep-ph].
12. Kolb, E. W.; Turner, M. S. (2019). "Dibaryons cannot be the dark matter". Physical Review D 99 (6): 063519. doi:10.1103/PhysRevD.99.063519. Bibcode2019PhRvD..99f3519K.
13. Gross, C.; Polosa, A.; Strumia, A.; Urbano, A.; Xue, W. (2018). "Dark matter in the standard model?". Physical Review D 98 (6): 063005. doi:10.1103/PhysRevD.98.063005. Bibcode2018PhRvD..98f3005G.
14. Farrar, G. R. (2003). "A Stable H-Dibaryon: Dark Matter, Candidate Within QCD?". International Journal of Theoretical Physics 42 (6): 1211–1218. doi:10.1023/A:1025702431127.
15. Farrar, G. R. (4 July 2019). "Stable Sexaquark: Dark Matter predictions, constraints and lab detection". Quy Nhon Workshop.
16. Azizi, K.; Agaev, S. S.; Sundu, H. (2020). "The Scalar Hexaquark uuddss: a Candidate to Dark Matter?". Journal of Physics G: Nuclear and Particle Physics 47 (9): 095001. doi:10.1088/1361-6471/ab9a0e. Bibcode2020JPhG...47i5001A.
17. Lyu, Yan; Tong, Hui; Sugiura, Takuya; Aoki, Sinya; Doi, Takumi; Hatsuda, Tetsuo; Meng, Jie; Miyamoto, Takaya (2021-08-11). "Dibaryon with Highest Charm Number near Unitarity from Lattice QCD". Physical Review Letters 127 (7): 072003. doi:10.1103/PhysRevLett.127.072003.