Are the leptons in $\beta^-$ decay already present in the nucleus in some form? In beta minus decay,  beta-minus particle and anti-neutrino are ejected, leaving behind daughter nucleus. $\beta^-$ and anti-neutrino both are leptons. 


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*Were the leptons already present in the nucleus in some form?

*Weak interactions are responsible for various processes here (and transformation of bosons).But, anyhow, if the above leptons are created, then can we call leptons elementary & indivisible?

*Are above leptons mass equivalent of some released energy?

*Is the transformation of quarks (neutron to proton conversion) and bosons ($W^+,W^-,Z$) the only cause of creation of above leptons?
...SIMILAR process for beta-minus and plus decay. Only neutron-proton conversion opposite, there's positron instead of electron, neutrino instead of anti-neutrino. My question about creation of leptons remains the same.

 A: *

*No.
A pair of neutrinos is pulled from the vacuum.  One of them interacts with one of the quarks via the weak force, and they both change identity: the quark to another kind, thus changing the neucleon; the neutrino to an electron, which escapes. (The negative charge unit also moved from the quark to the lepton.)  The electron escapes as the beta radiation, along with the anti-neutrino that goes unnoticed.

*They are created as opposed pairs.  They are elementary.  The W doesn't leave the diagram if you draw a Feynman diagram. If you elaborate more you can show that this can be represented as a temporary pair, but we usually don't. 

*The mass of the created particles indeed is counted. It comes from the potential energy in the binding energy of the neucleus: that's why it decays! Changing a neutron to a proton releases energy as it's bound tighter, and that more than pays for the particle mass and kenetic energy.

*Yes, the weak interaction is "the same" between pairs of quarks or leptons of various kinds. That's a key symmetry and organizational principle in understanding the standard model particles.  In all cases using W, one particle changes to its partner with the different charge. With Z it's just like electrtic force in that it doesn't change the types or move the charge around.
A: Leptons are not present inside the nucleus or in the nucleons(protons and neutrons). Instead what happens is the W- boson is created and this turns the down quark into an up quark. The W- boson then gets converted into an electron and an electron antineutrino. 
The leptons are created from W- boson and are fundamental. 
The mass of the ejected particles comes from the energy of turning the neutron into a proton. 
The creation of leptons are similar except opposite if the W+ is used and there are no changes if Z boson is used.
