Pentaquark

Two models of a generic pentaquark
A five-quark "bag"
A "meson-baryon molecule"
A q indicates a quark and a q an antiquark. Gluons (wavy lines) mediate strong interactions between quarks. Red, green, and blue colour charges must each be present, while the remaining quark and antiquark must share a colour and its anticolour, in this example blue and antiblue (shown as yellow).

A pentaquark is a human-made subatomic particle, consisting of four quarks and one antiquark bound together; they are not known to occur naturally, or exist outside of experiments specifically carried out to create them.

As quarks have a baryon number of ⁠++1/3⁠, and antiquarks of ⁠−+1/3⁠, the pentaquark would have a total baryon number of 1, and thus would be a baryon. Further, because it has five quarks instead of the usual three found in regular baryons (a.k.a. "triquarks"), it is classified as an exotic baryon. The name pentaquark was coined by Claude Gignoux et al. (1987)[1] and Harry J. Lipkin in 1987;[2] however, the possibility of five-quark particles was identified as early as 1964 when Murray Gell-Mann first postulated the existence of quarks.[3] Although predicted for decades, pentaquarks proved surprisingly difficult to discover and some physicists were beginning to suspect that an unknown law of nature prevented their production.[4]

The first claim of pentaquark discovery was recorded at LEPS in Japan in 2003, and several experiments in the mid-2000s also reported discoveries of other pentaquark states.[5] However, other researchers were not able to replicate the LEPS results, and the other pentaquark discoveries were not accepted because of poor data and statistical analysis.[6] On 13 July 2015, the LHCb collaboration at CERN reported results consistent with pentaquark states in the decay of bottom Lambda baryons (Λ0
b).[7] On 26 March 2019, the LHCb collaboration announced the discovery of a new pentaquark that had not been previously observed.[8] On 5 July 2022, the LHCb collaboration announced the discovery of the PΛ
ψs(4338)0[a] pentaquark.[9]

Outside of particle research laboratories, pentaquarks might be produced naturally in the processes that result in the formation of neutron stars.[10]

  1. ^ Gignoux, C.; Silvestre-Brac, B.; Richard, J.M. (1987-07-16). "Possibility of stable multiquark baryons". Physics Letters B. 193 (2): 323–326. Bibcode:1987PhLB..193..323G. doi:10.1016/0370-2693(87)91244-5.
  2. ^ Lipkin, H.J. (1987). "New possibilities for exotic hadrons — anticharmed strange baryons". Physics Letters B. 195 (3): 484–488. Bibcode:1987PhLB..195..484L. doi:10.1016/0370-2693(87)90055-4.
  3. ^ "Observation of particles composed of five quarks, pentaquark-charmonium states, seen in Λ0
    b    →J/ψpK− decays"    . LHCb (Press release). CERN. 14 July 2015. Retrieved 2015-07-14.
  4. ^ Muir, H. (2 July 2003). "Pentaquark discovery confounds sceptics". New Scientist. Retrieved 2010-01-08.
  5. ^ Hicks, K. (23 July 2003). "Physicists find evidence for an exotic baryon". Ohio University. Archived from the original on 8 September 2016. Retrieved 2010-01-08.
  6. ^ See p. 1124 in Amsler, C.; et al. (Particle Data Group) (2008). "Review of particle physics" (PDF). Physics Letters B. 667 (1–5): 1–6. Bibcode:2008PhLB..667....1A. doi:10.1016/j.physletb.2008.07.018. hdl:1854/LU-685594. S2CID 227119789.
  7. ^ Aaij, R.; et al. (LHCb collaboration) (2015). "Observation of J/ψp resonances consistent with pentaquark states in Λ0
    b    →J/ψK−p decays". Physical Review Letters. 115 (7): 072001. arXiv:1507.03414. Bibcode:2015PhRvL.115g2001A. doi:10.1103/PhysRevLett.115.072001. PMID 26317714. S2CID 119204136.
  8. ^ "LHCb experiment discovers a new pentaquark". CERN. 26 March 2019. Retrieved 26 April 2019.
  9. ^ "Observation of a strange pentaquark, a doubly charged tetraquark and its neutral partner". July 5, 2022. Retrieved July 5, 2022.
  10. ^ Sample, I. (14 July 2015). "Large Hadron Collider scientists discover new particles: pentaquarks". The Guardian. Retrieved 2015-07-14.


Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).