What is charm number?

Charm number is a quantum number used in particle physics to describe the properties of hadrons containing charm quarks. It was first introduced in 1974 by Sheldon Lee Glashow, James Bjorken, and John Iliopoulos to explain the suppression of certain weak decays in mesons and baryons.

The charm number, denoted as C, has a value of +1 for charm quarks and -1 for charm antiquarks. This means that a hadron containing one charm quark and one charm antiquark has a charm number of zero.

The charm number is conserved in strong interactions but can change in weak interactions, such as the decay of particles containing charm quarks. The conservation of charm number is related to the conservation of the so-called charm quantum number, which is a combination of charm number and strangeness number.

The charm number is an important tool for understanding the properties of hadrons containing charm quarks, such as the J/psi particle and the D mesons. It also plays a role in the study of CP violation in weak decays of these particles.