Physicists in Italy have discovered the first evidence of a rare nucleus that doesn’t exist in nature and lives for just 10-10 seconds before decaying. It’s a type of hypernucleus that, like all nuclei, contains an assortment of neutrons and protons. But unlike ordinary nuclei, hypernuclei also contain at least one hyperon, a particle that consists of three quarks, including at least one strange quark. Hypernuclei are thought to form the core of strange matter that may exist in distant parts of the universe, and could also allow physicists to probe the inside of the nucleus.
The particular hypernucleus investigated here, called “hydrogen six Lambda” (6ΛH), was first predicted to exist in 1963. Now, in a study published in a recent issue of Physical Review Letters, physicists working in the FINUDA experiment at the Istituto Nazionale di Fisica Nucleare – Laboratori Nazionali di Frascati (INFN-LNF) in Frascati, Italy, have reported finding the first evidence for the particle. The FINUDA collaboration’s analysis of millions of events has turned up three events for the rare hypernucleus.
Strange properties – As its name suggests, 6ΛH is a large type of hydrogen nucleus that consists of six particles: four neutrons, one proton, and one Lambda (Λ) hyperon. Since an ordinary hydrogen nucleus contains one proton and no neutrons, hydrogen nuclei that contain one or more neutrons are sometimes called “heavy hydrogen.” The most common types of heavy hydrogen are deuterium (which has one neutron) and tritium (which has two neutrons). Since 6ΛH has four neutrons plus a L hyperon, physicists refer to it as “heavy hyperhydrogen.”
The L hyperon, which consists of one up, one down, and one strange quark, does an even more interesting thing to 6ΛH: it increases its lifetime from 10-22 seconds (the lifetime of the hypernucleus core 5H without L) to 10-10 seconds. When scientists first discovered the L hyperon in 1947, they observed a similarly longer lifetime than predicted for this “strange” object. That observation led to the idea of the existence of the strange quark, with strangeness being the property that causes the quark to live so long.