GHOSTS IN THE MACHINE
Physicists are homing in on the mass of the neutrino, nature’s most elusive subatomic particle. The latest super-accurate measurement, made by an experiment in Germany, shows that the neutrino is around half a million times less massive than the electron, the lightest particle of normal atomic matter. According to the Standard Model, the high point of 300 years of physics which describes the fundamental building blocks of matter and three non-gravitational forces that glue them together, the neutrino should be massless. So why should we care about a mass measurement (no matter how tiny) of a neutrino? Well, it may provide vital clues to the fabled ‘theory of everything’ – a deeper, more fundamental theory of physics of which the Standard Model is believed to be but an approximation.
HUNTING THE ELUSIVE GHOST PARTICLE
The latest neutrino measurement was made in Karlsruhe, Germany, where physicists exploited the ‘beta decay’ of tritium. Tritium is a heavy type – or ‘isotope’ – of hydrogen. In beta decay, the unstable core – the ‘nucleus’ – of an atom sheds surplus energy by spitting out an electron and an antineutrino (the neutrino and its ‘antimatter’ twin have the same mass). Neutrinos are fantastically antisocial, interacting so rarely with
