Exotic is the word! Italian physicists have discovered traces of rare nuclei containing an exotic form of matter – hyperons. They have just discovered a hydrogen nucleus with 6 nucleons, which includes 4 neutrons, 1 proton (and thus hydrogen) and one uncharged hyperon called lambda!!
The exotic side of the Universe
Hyperons are particles, which are made up of quarks, just like protons. But, unlike protons, they are short-lived, much heavier and contain the so-called strange quark. They are thus called strange baryons! If a nucleus contains such hyperons, the nucleus is called ‘hypernucleus’.
The Italian scientists have found a hypernucleus called ‘hydrogen six Lambda’ (6ΛH, Λ=Greek letter, Lambda), which means that it is a hydrogen nucleus (i.e. has 1 proton), with six nucleons altogether (i.e. 5 particles other than the proton) and that one of them is the Lambda baryon. This says that the other four particles are all neutrons. The 6ΛH was predicted in 1963, but only now have physicists at Instituto Nazionale di Fisica Nucleare-Laboratori Nazionali di Frascati (INFN-LNF) working on this experiment called FINUDA found a signature of it. The finding is due to appear in an issue of the Physical Review Letters (PRL).
The hyperon makes it possible to detect this hydrogen nucleus having as many as 4 neutrons. Hydrogen five (5H), i.e. without the Lambda, exists for just 10-22 s, which is too short to measure leave alone trap and study the nucleus. The presence of the strange particle boosts the lifetime by a factor of a trillion, taking it to 0.1 nanosecond, which is long enough for physicists to measure and study. Note that this timescale is still way too small for daily life!
Producing the hyperhydrogen
The hyperhydrogen is produced in an indirect way. The FUNIDA collider collides electron-positron beams. This gives rise to a phi-meson (with a small probability). This phi-meson can decay into two other mesons – the K meson and the anti-K meson. When the anti K-meson (which contains a strange quark) interacts with a lithium nucleus, it can produce a 6ΛH and pi-plus meson. When physicists detect the pi-plus meson, they know that a 6ΛH has been created.
FUNIDA experiments have also been able to produce 4ΛH, having 2 neutrons. They are produced more readily than 6ΛH and can be studied with greater ease as they exist for a longer time than the 6ΛH.
Clues into strangeness
Physicists are hoping that such studies will yield valuable clues into the nature of strange forms of matter. Another interesting challenge will be to synthesize nuclei having two strange particles, rather than just one! Producing helium or lithium nuclei with strange particle is also on the cards.
If you have a technical bent of mind, here is the link to the PRL paper: http://prl.aps.org/abstract/PRL/v108/i4/e042501 (If you’re not affiliated to an institute having a PRL account, you’ll have to buy the paper to read it.)