Hypertriton

Hypertriton, designated 3ΛH, is the lightest known hypernucleus. It consists of a proton, a neutron, and a bound Lambda hyperon, effectively a Λ bound to a deuteron-like core. The Λ carries strangeness −1, giving the nucleus a nonzero strangeness quantum number.

Structure and properties: The Λ–nucleon interaction in this system is weak, resulting in a very small Lambda-separation energy of about 0.1 MeV. Consequently, the hypertriton is extremely weakly bound compared with ordinary nuclei. The ground state is generally taken to have total spin and parity J^P = 1/2+; the isospin is zero since the Λ is an isospin-0 particle. The mass is only slightly less than the sum of the masses of its three constituents due to the small binding energy.

Lifetime: Hypertritons decay weakly, predominantly via decay of the Lambda, so their lifetime is close to that of the free Λ hyperon, around 2.6 × 10^−10 seconds, with possible small medium-modification effects in the nuclear environment.

Production and significance: Hypertritons have been produced and observed in high-energy heavy-ion collisions at facilities such as RHIC and the LHC, as well as in fixed-target experiments and cosmic-ray interactions. Studying 3ΛH helps constrain the hyperon–nucleon interaction, three-body forces in strange nuclear matter, and the equation of state for dense astrophysical objects like neutron stars.

History: The hypertriton was among the earliest hypernuclei observed in cosmic-ray and emulsion experiments, contributing to the development of hypernuclear physics.