The lambda baryon was first discovered in October 1950, by V. D. Hopper and S. Biswas of the
University of Melbourne, as a neutral
V particle with a
proton as a decay product, thus correctly distinguishing it as a
baryon, rather than a
meson, i.e. different in kind from the
K meson discovered in 1947 by
George Rochester and
Clifford Charles Butler; they were produced by cosmic rays and detected in photographic emulsions flown in a balloon at . Though the particle was expected to live for , it actually survived for . In 2011, the international team at
JLab used high-resolution spectrometer measurements of the reaction H(e, e′K+)X at small Q2 (E-05-009) to extract the pole position in the complex-energy plane (primary signature of a resonance) for the Λ(1520) with mass and width , which seem to be smaller than their Breit–Wigner values. This was the first determination of the pole position for a
hyperon. The lambda baryon has also been observed in atomic nuclei called
hypernuclei. These nuclei contain the same number of protons and neutrons as a known nucleus, but also contains one or in rare cases two lambda particles. In such a scenario, the lambda slides into the center of the nucleus (it is not a proton or a neutron, and thus is not affected by the
Pauli exclusion principle), and it binds the nucleus more tightly together due to its interaction via the strong force. In a
lithium isotope (), it made the nucleus 19% smaller. == Types ==