Down quark

The down quark $d$ is the first-generation down-type quark, with electric charge $-e/3$, spin $1/2$ and baryon number $1/3$. Together with the up quark, it supplies the net valence flavor content of ordinary protons and neutrons.^[ref]

The minimal neutron content $udd$ has total electric charge zero and baryon number one. In beta decay, a down-to-up weak charged current can turn a neutron into a proton, accompanied by the required leptons. This is a flavor change, rather than an electron previously stored inside the neutron escaping. Additional quark pairs and gluons are part of the full hadron state.