In a beta decay event, a neutron can transform into a proton, an electron, and an electron antineutrino (or vice versa, depending on whether it is a beta-minus or beta-plus decay). The neutron, which is composed of three quarks (two down quarks and one up quark), undergoes a transformation at the quark level during the decay process.
When a neutron decays, one of its down quarks changes into an up quark, resulting in the formation of a proton. The other two quarks (the remaining down quark and two up quarks) remain unchanged and form the newly created proton.
So, in a beta decay event, the neutron essentially transforms into a proton while releasing an electron and an electron antineutrino. The proton is positively charged and remains in the nucleus, while the electron and electron antineutrino are emitted as beta particles and can travel away from the nucleus.
It's important to note that in beta decay, the total number of protons and neutrons (the atomic number and mass number) is conserved. While a neutron transforms into a proton, the total number of nucleons (protons and neutrons) in the nucleus remains the same.