Question

40. Which of the following is not necessarily conserved? AND PLEASE EXPLAIN WHY. :) A. lepton number B. baryon number C. meson number D. energy

hint, the answer-key says C.

Answer 1

a) Lepton Number: The conservation of lepton number means that whenever a lepton of a certain generation is created or destroyed in a reaction, a corresponding antilepton from the same generation must be created or destroyed. Each lepton has a lepton number of 1 and each antilepton has a lepton number of -1. Other non-leptonic particles have a lepton number of 0. The lepton number is a conserved quantum numberin all particle reactions.

b) Baryon Number: The baryon number is conserved in nearly all the interactions of the Standard Model. It means that the sum of the baryon number of all incoming particles is the same as the sum of the baryon numbers of all particles resulting from the reaction.

c) Meson Number: It is not conserved as pion is a meson composed of a quark and an antiquark, and on the right side of the equation there are only leptons.

^-  -> ^- +

d) Energy: The total energy of an isolated system remains constant, it is said to be conserved over time. This law means that energy can neither be created nor destroyed; rather, it can only be transformed from one form to another.