The best study of the rare "atom" consisting
of two electrons and one positron is being reported.
(abbreviated Ps) is a very "clean" two-body object: it consists of
an electron and a positron which after about 150 nanoseconds
annihilate each other. For studying the theory of quantum
electrodynamics (QED), Ps is in some ways better even than the
hydrogen atom: with pointlike constituents and with no complicating
nuclear forces (the size of the proton and its own internal
structure interject uncertainties into QED estimates of hydrogen behavior),
Ps is a simpler, albeit fragile, quantum system.
An even more
fragile "atom" is the tripartite object consisting of two electrons
and one positron.
Ps-, as it is known, is less suitable for QED
studies than Ps, but has the great virtue of being the simplest
three-body system in physics. Again, it is simpler than H-,
and helium because of its pointlike constituents and the absence of
Ps- is, like Ps, a bound state with discrete
quantum energy states, although only the ground state is calculated
to be stable against dissociation into Ps and a free electron. Very
little is known about Ps- beyond its lifetime.
Now, a new
experiment carried out at the Max Planck Institute for Nuclear
Physics in Heidelberg has measured the lifetime of Ps- with a
sixfold increase in precision (the new value is half a nanosecond).
Ps- is formed by shooting a positron beam into a thin carbon foil,
and its size is actually a bit bigger than a hydrogen atom.
Fleischer et al.,
Physical Review Letters, upcoming article
Contact: Frank Fleischer,