What is "lambda baryon"

n. (context physics English) Any of three particles, having no electric charge and an isotopic spin of 1, composed of an up quark, down quark and either a strange quark, a charm quark or a bottom quark

The Lambda baryons are a family of subatomic hadron particles that have the symbols , , , and and have +1 elementary charge or are neutral. They are baryons containing three different quarks: one up, one down, and one third quark, which can be a strange , a charm , a bottom , or a top quark. The top Lambda is not expected to be observed as the Standard Model predicts the mean lifetime of top quarks to be roughly . This is about one-twentieth the timescale for strong interactions, and, therefore it does not form hadrons.

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 Rochester and 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 . The property that caused it to live so long was dubbed strangeness and led to the discovery of the strange quark. Furthermore, these discoveries led to a principle known as the conservation of strangeness, wherein lightweight particles do not decay as quickly if they exhibit strangeness (because non-weak methods of particle decay must preserve the strangeness of the decaying baryon).

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 (Λ7Li), it made the nucleus 19% smaller.