The electron is an elementary particle, part of the SM, pointlike, with no substructure, or spatial extent. Its intrinsic properties include its EM charge, which we still call the elementary charge.
Originally the name electron comes from electric ion, and it was discovered around the 1900s.
Though we still call it (the electron's Em charge) the elementary charge. Since we call it the elementary charge, it was believed that every single object in the universe had a EM charge that was larger (multiples) then the elementary charge, and the elementary charge of the electron was indivisible.
The elementary charge is a fundamental physical constant.
Charge quantization is the principle that the charge of any object is an integer multiple of the elementary charge. Thus, an object's charge can be exactly 0 e, or exactly 1 e, −1 e, 2 e, etc., but not, say, (1/2)e, or −3.8 e, etc. This is the reason for the terminology "elementary charge": it is meant to imply that it is an indivisible unit of charge.
Now in 1964, we discovered the down quark, with EM charge of one third of the electron. Since then, the elementary EM charge should be that of the down quark, and the electron should have three times the elementary EM charge (of the down quark).
Now I believe that the true elementary EM charge is the down quark and its EM charge should be the fundamental physical constant.
I do understand that quarks are in confinement and have never been observed outside confinement experimentally, but still I believe that the down quark charge is the real indivisible elementary EM charge.
- Why do we still call the electron the elementary EM charge and why is the -e still the fundamental physical constant (and not the down quark)?