I heard that 'bosons' are particles made from a quark and an anti-quark. Is this true? If it is, then how come they do not to annihilate each other?

Asked by: Adam

Answer

First of all, it is true that a particle that is formed from a quark and an anti-quark is a boson. But the term 'boson' refers to a much broader class of particles. Quark/anti-quark bound states are referred to by physicists as 'mesons.' But any particle with integer intrinsic spin angular momentum is a boson. This includes mesons like pions, gauge particles like photons and gluons, the hypothesized Higgs scalar, etc.

To answer your second question, quark/anti-quark pairs (mesons) do annihilate one another! There are no stable mesons that we have ever discovered. Their lifetimes range from 10^-8 to 10^-16 seconds, but this is long enough for us to detect their presence in particle accelerator experiments and to measure their properties. Incidently, before the quark theory was invented to understand the properties of elementary particles the term 'meson' was also applies to muons -- which are not made up of quarks but are fundamental point particles like the electron. Unfortunately some people still use this confusedly anachronistic term to refer to muons!
Answered by: Brent Nelson, M.A. Physics, Ph.D. Student, UC Berkeley