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[citation needed]. 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]

See also


  1. ^ a b "Oddball sexaquark particles could be immortal, if they exist at all".
  2. ^ Vijande, J.; Valcarce, A.; Richard, J.-M. (2011). "Stability of hexaquarks in the string limit of confinement". Physical Review D. 85 (1): 014019. arXiv:1111.5921. Bibcode:2012PhRvD..85a4019V. doi:10.1103/PhysRevD.85.014019. S2CID 53511291.
  3. ^ Belz, J.; et al. (BNL-E888 Collaboration) (1996). "Search for the weak decay of an H dibaryon". Physical Review Letters. 76 (18): 3277–3280. arXiv:hep-ex/9603002. Bibcode:1996PhRvL..76.3277B. doi:10.1103/PhysRevLett.76.3277. PMID 10060926. S2CID 15729745.
  4. ^ Stotzer, R. W.; et al. (BNL-E888 Collaboration) (1997). "Search for H dibaryon in 3He (K, K+) Hn". Physical Review Letters. 78 (19): 3646–36490. Bibcode:1997PhRvL..78.3646S. doi:10.1103/PhysRevLett.78.3646.
  5. ^ Alavi-Harati, A.; et al. (KTeV Collaboration) (2000). "Search for the weak decay of a lightly bound H0 dibaryon". Physical Review Letters. 84 (12): 2593–2597. arXiv:hep-ex/9910030. Bibcode:2000PhRvL..84.2593A. doi:10.1103/PhysRevLett.84.2593. PMID 11017277. S2CID 119068614.
  6. ^ Ambartsumyan, V. A.; Saakyan, G. S. (1960). "The Degenerate Superdense Gas of Elementary Particles". Soviet Astronomy. 37: 193. Bibcode:1960SvA.....4..187A.
  7. ^ Kagiyama, S.; Nakamura, A.; Omodaka, T. (1992). "Compressible bag model and dibaryon stars". Zeitschrift für Physik C. 56 (4): 557–560. Bibcode:1992ZPhyC..56..557K. doi:10.1007/BF01474728. S2CID 121769383.
  8. ^ 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. arXiv:nucl-th/9706080. Bibcode:1997PhRvC..56.1576F. doi:10.1103/PhysRevC.56.1576. S2CID 119392781.
  9. ^ "Forschungszentrum Jülich press release".
  10. ^ "Massive news in the micro-world: a hexaquark particle".
  11. ^ Adlarson, P.; et al. (2014). "Evidence for a New Resonance from Polarized Neutron-Proton Scattering". Physical Review Letters. 112 (2): 202301. arXiv:1402.6844. Bibcode:2014PhRvL.112t2301A. doi:10.1103/PhysRevLett.112.202301. S2CID 2280323.
  12. ^ Bashkanov, M. (2020). "A new possibility for light-quark dark matter". Journal of Physics G. 47 (3): 03LT01. arXiv:2001.08654. Bibcode:2020JPhG...47cLT01B. doi:10.1088/1361-6471/ab67e8. S2CID 210861179.
  13. ^ "Physicists Think We Might Have a New, Exciting Dark Matter Candidate".
  14. ^ "Did this newfound particle form the universe's dark matter?".
  15. ^ "Did German physicists accidentally discover dark matter in 2014?".
  16. ^ Williams, M. (11 March 2020). "Is the "D-star Hexaquark" the Dark Matter Particle?". Universe Today.
  17. ^ "Ask Ethan: It's Absurd To Think Dark Matter Might Be Made Of Hexaquarks, Right?".
  18. ^ Jaffe, R. L. (1977). "Perhaps a Stable Dihyperon?" (PDF). Physical Review Letters. 38 (5): 195–198. Bibcode:1977PhRvL..38..195J. doi:10.1103/PhysRevLett.38.195. OSTI 1446298.
  19. ^ Farrar, G. R. (2017). "Stable Sexaquark". arXiv:1708.08951 [hep-ph].
  20. ^ Kolb, E. W.; Turner, M. S. (2019). "Dibaryons cannot be the dark matter". Physical Review D. 99 (6): 063519. arXiv:1809.06003. Bibcode:2019PhRvD..99f3519K. doi:10.1103/PhysRevD.99.063519. S2CID 86859713.
  21. ^ Gross, C.; Polosa, A.; Strumia, A.; Urbano, A.; Xue, W. (2018). "Dark matter in the standard model?". Physical Review D. 98 (6): 063005. arXiv:1803.10242. Bibcode:2018PhRvD..98f3005G. doi:10.1103/PhysRevD.98.063005. S2CID 119213361.
  22. ^ 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. S2CID 122452089.
  23. ^ Farrar, G. R. (4 July 2019). "Stable Sexaquark: Dark Matter predictions, constraints and lab detection" (PDF). Quy Nhon Workshop.
  24. ^ 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. arXiv:1904.09913. Bibcode:2020JPhG...47i5001A. doi:10.1088/1361-6471/ab9a0e. S2CID 127956495.