Pentaquark
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.
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.
[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 (Λ0b).
[9] Outside of particle research laboratories, pentaquarks might be produced naturally in the processes that result in the formation of neutron stars.
The conclusion that pentaquarks in general, and the Θ+, in particular, do not exist, appears compelling.The 2008 Review of Particle Physics went even further:[6] There are two or three recent experiments that find weak evidence for signals near the nominal masses, but there is simply no point in tabulating them in view of the overwhelming evidence that the claimed pentaquarks do not exist...
In July 2015, the LHCb collaboration at CERN identified pentaquarks in the Λ0b→J/ψK−p channel, which represents the decay of the bottom lambda baryon (Λ0b) into a J/ψ meson (J/ψ), a kaon (K−) and a proton (p).
The major challenge in these studies is a heavy mass of the pentaquark, which will be produced at the tail of photon-proton spectrum in JLab kinematics.
[21] This process has a large cross-section due to lack of electroweak intermediaries and gives access to pentaquark wave function.
In the fixed-target experiments pentaquarks will be produced with small rapidities in laboratory frame and will be easily detected.
[8] Designated Pc(4312)+ (Pc+ identifies a charmonium-pentaquark while the number between parenthesis indicates a mass of about 4312 MeV), the pentaquark decays to a proton and a J/ψ meson.
Designated PψsΛ(4338)0, its composition is described as udscc, representing the first confirmed pentaquark containing a strange quark.
[25] The discovery of pentaquarks will allow physicists to study the strong force in greater detail and aid understanding of quantum chromodynamics.
c type pentaquark possibly discovered in July 2015, showing the flavours of each quark and one possible colour configuration.
b into a kaon K −
and a pentaquark P +
c .
b →J/ψK −
p decay, with each fit component shown individually. The contribution of the pentaquarks are shown by hatched histograms .
