xi0

Xi0 is a neutral baryon belonging to the cascade family, denoted Ξ0. It is a spin‑1/2 particle that contains two strange quarks and one up quark, giving it the quark composition ssu. The mass of the Xi0 is approximately 1314.86 MeV/c², slightly heavier than the proton but lighter than many heavier hyperons. The parity of the state is positive, as inherited from its quark constituents, and it participates in the same SU(3) flavour multiplet as other strange baryons such as the Λ, Σ, and Ξ- particles.

The Xi0 was first observed experimentally in the 1950s using bubble chamber detectors. Its discovery helped confirm the existence of hyperons predicted by the Eightfold Way classification scheme of Gell-Mann and Nehru. Subsequent experiments at CERN (e.g., WA76, WA77) and SLAC have refined its properties and measured its lifetime, which is on the order of 10⁻¹⁰ seconds. The dominant decay mode of the Xi0 is into Λπ⁰ with a branching ratio of about 99.9%. The Λ baryon itself subsequently decays into a proton and a negative pion, providing a clear experimental signature.

Xi0 plays a key role in studies of weak decay processes and CP violation in the strange quark sector. Its relatively long lifetime compared with many other hyperons allows it to travel measurable distances in particle detectors, facilitating detailed tracking of its decay products. Moreover, the Xi0, together with other strange baryons, serves as a probe for the strong interaction in the non‑perturbative regime of quantum chromodynamics (QCD). Theoretical models, including lattice QCD calculations and quark potential models, attempt to reproduce its mass and decay constants, offering insight into the dynamics of strange quarks within baryons.

In astrophysics, neutral cascade baryons such as Xi0 may appear in the cores of neutron stars, where extreme densities could favor the conversion of nucleons into hyperons, affecting the equation of state and observable stellar properties. Experimental searches for hyperon‑rich environments thus consider Xi0 as an important component in high‑density QCD studies.