By Mary and Ian
Butterworth, Imperial College London, and Doris and Vigdor
Teplitz, Southern Methodist University, Dallas, Texas, USA.
The Higgs boson is a hypothesised particle which, if it exists,
would give the mechanism by which particles acquire mass.
Matter is made of molecules; molecules of atoms; atoms of a
cloud of electrons about one-hundred-millionth of a centimetre
and a nucleus about one-hundred-thousandth the size of the
electron cloud. The nucleus is made of protons and neutrons.
Each proton (or neutron) has about two thousand times the mass
of an electron. We know a good deal about why the nucleus is so
small. We do not know, however, how the particles get their
masses. Why are the masses what they are? Why are the ratios of
masses what they are? We can't be said to understand the
constituents of matter if we don't have a satisfactory answer to
this question.
Peter Higgs has a model in which particle masses arise in a
beautiful, but complex, progression. He starts with a particle
that has only mass, and no other characteristics, such as
charge, that distinguish particles from empty space. We can call
his particle H. H interacts with other particles; for example if
H is near an electron, there is a force between the two. H is of
a class of particles called "bosons". We first attempt a more
precise, but non-mathematical statement of the point of the
model; then we give explanatory pictures.
In the mathematics of quantum mechanics describing creation and
annihilation of elementary particles, as observed at
accelerators, particles at particular points arise from "fields"
spread over space and time. Higgs found that parameters in the
equations for the field associated with the particle H can be
chosen in such a way that the lowest energy state of that field
(empty space) is one with the field not zero. It is surprising
that the field is not zero in empty space, but the result, not
an obvious one, is: all particles that can interact with H gain
mass from the interaction.
Thus mathematics links the existence of H to a contribution to
the mass of all particles with which H interacts. A picture that
corresponds to the mathematics is of the lowest energy state,
"empty" space, having a crown of H particles with no energy of
their own. Other particles get their masses by interacting with
this collection of zero-energy H particles. The mass (or inertia
or resistance to change in motion) of a particle comes from its
being "grabbed at" by Higgs particles when we try and move it.
If particles no get their masses from interacting with the empty
space Higgs field, then the Higgs particle must exist; but we
can't be certain without finding the Higgs. We have other hints
about the Higgs; for example, if it exists, it plays a role in
"unifying" different forces. However, we believe that nature
could contrive to get the results that would flow from the Higgs
in other ways. In fact, proving the Higgs particle does not
exist would be scientifically every bit as valuable as proving
it does.
