Beta decay breaks conservation of momentum? Just considering the decay of a free neutron, the change in rest mass, .732-ish MeV, leaves as kinetic energy of the electron and neutrino. Doesnt this break conservation of momentum since the neutron has no momentum? What am I missing, is there really a mass-energy-momentum conservation and momentum conservation on its own doesnt exist for beta decay?
In math, before = after, is
pn = pe + pp + pv
Or
E + p = sum of E + sum of p
Or something else?
 A: Energy and momentum are definitely conserved in beta decay. Note that free neutron decay is different from
nuclear beta decay where the original neutron is not free and is bound to a nucleus.
Also, in the decay $$n\rightarrow p+e^-+\bar\nu$$ the kinetic energy of the resulting proton and nucleus (in the beta-decay version) must also be taken into account and not just the "kinetic energy of the electron and neutrino". You'll find that energy and momentum are conserved (in either case).
A: Edit after the question was edited to include the proton in the decay products
Momentum is a vector quantity and the four vector algebra has to be used when discussing decays and conservation laws at particle level. The equation for the momentum is
$P_xn=p_xp+p_xν+p_xe$
$P_yn=p_yp+p_yν+p_ye$
$P_zn=p_zp+p_zν+p_ze$
If in the center of mass of the neutron, when P is equal to zero, conservation requires for the sum to be zero.
and for energy
En=Ep+Eν+Ee
Where E is the total energy in the system, all to be computed with the four vector algebra  representing the particles . The "length" of the four vector is the invariant mass of the particle it represents.
