NEUTRINOS FEATURE
problem of beta decay for many months. And
the solution he came up with was radical.
Perhaps, in beta decay, the electron is not
alone, and is instead emitted along with
another particle. Think of the gun again. If
the bullet emerges from the muzzle with a
second projectile, then if the second
projectile takes only a small amount of
the total energy, the bullet will take the
lion’s share; if the second projectile
takes most of the available
energy, then the bullet might
very well have so little
energy it dribbles out of the
gun muzzle. Could this be
the solution to the beta
decay puzzle? Could there
really be a second particle
out there?
For such a particle to
have not shown up in anyexperiment, it would have to be elusive. Pauli
predicted its properties: zero electric charge,
zero mass and an ability to pass through
matter without being stopped. Pauli imagined
the particle penetrating a thickness of 10
centimetres of lead with no difficulty; later
physicists would realise that a layer of lead
many light-years thick would be necessary to
stop such a particle. Pauli christened the
hypothetical particle a ‘neutron’. But, with the
discovery of a chargeless counterpart of the
proton in 1932 – the neutron – the Italian
physicist Enrico Fermi would rename it the
‘neutrino’.
The neutrino was, in Pauli’s words, a
“desperate remedy”. “I have done a terrible
thing,” he said. “I have postulated a particle
that cannot be detected.” In fact, Pauli bet a
case of champagne that nobody would ever
manage to bag a neutrino. However, he had not
counted on human ingenuity... (Turn to p57)LEFT The main
spectrometer at the
KATRIN experiment.
KATRIN aims to
measure the mass of
the neutrino, vital for
understanding the
UniverseBELOW As a
neutrino enters the
bubble chamber, it
collides with an
electron giving it
enough energy to
cause charged
particles to travel in
helical paths, seen
here as curls
branching off the
neutrino’s pathunstable state to more stable state, a nucleus
sheds a well-defined amount of energy,
exactly like a gun firing a bullet. But bullets are
always ejected with the same energy. It is
never the case that one bullet shoots out at
high speed, the next at a lower speed, and
the one after so slowly it merely
dribbles out of the gun muzzle.
Pauli was in a good position to solve
the puzzle of beta decay, despite his
angst-ridden personal life. He was one
of the architects of quantum theory,
concocted in the mid-1920s to
describe the counterintuitive world
of the atom and its constituents.
Famously, at the end of a lecture
given by Einstein, he had stood up
and told the audience: “What
Professor Einstein said is not
entirely stupid.”
Pauli wrestled with the