U4T3:SM.2

Baryon number is defined as a quantum number of a system defined by B=1/3*(number of quarks - number of anti-quarks).

Lepton number is defined as a conserved quantum number representing the difference between the number of leptons and the number of antileptons in an elementary particle interaction, defined by L=(number of leptons - number of antileptons).

Baryon number and lepton number are always conserved in a reaction. Baryon and lepton number are the same before and after an interactions, therefore are conserved.

<p>Electrons move closer together. Repulsive charge between the negatively charged electrons gets stronger, causing them to slow down. At some point when the electrons are close enough, they exchange a (virtual) photon. After the interaction the two electrons move away from each other with changed velocities.</p> Signup and view all the answers

<p>Electron and position move closer together. When close enough they interact and exchange a virtual photon (y) and scatter off each other with just their velocities changed.</p> Signup and view all the answers

<p>An electron and positron approach each other. As they get closer, they annihilate each other instead of scattering off. This annihilation forms a virtual photon (y). This virtual photon's energy (y) is then used to form a new electron-positron pair.</p> Signup and view all the answers

<p>A neutron (udd quark composite) decays to become a proton (uud quark composite) so a down quark turns into an up quark producing a W boson. This W boson immediately decays into an electron and an electron neutrino. This is the process of beta negative decay and is sometimes called quark flavour change.</p> Signup and view all the answers