Why was the expected emission energy of the beta particle not higher than the greatest energy value on the beta emission energy spectrum graph? 
In the above physics question the correct answer says that the expected emission energy of the beta particle should be the max kinetic energy shown on the graph at E2.
I think the answer's reasoning is probably that the emitted beta particles could lose a range of energy due to the emitted neutrino so the graph represents E2(original energy of beta particle)-energy of neutrino(which can take on a range of values from 0)
However shouldn't the expected value be greater than E2 simply because the neutrino should always subtract from the energy of the emitted beta particle by mass energy conservation? E2 should then represent the maximum possible energy of the beta particle after subtracting the minimum mass+energy of the neutrino(which is not 0). Thus the expected value should have been greater than E2. I'm assuming that the emission of the beta particle always results in the emission of a neutrino.
 A: Technically you are correct. The totaI energy available is the difference $\Delta$ between the initial and final nuclear states, which is a fixed amount. If the only particle emitted were the beta, then the KE of the beta would also be a fixed amount $E_0=\Delta - M$, where $M$ is the rest mass energy of the beta. If in addition to the beta there is a neutrino emitted with rest-mass energy $m$, the KE of the beta would range from $0$ to $E_2=\Delta - M - m$ . So $E_0=E_2+m$.
If $m \gt 0$ then $E_0 \gt E_2$ - ie the maximum KE of betas is less than it would be if no neutrino is emitted. However, in the Standard Model the neutrino is massless. The present upper estimate of its mass is $m=0.161$ eV compared with $M=0.511$ MeV for the beta (electron). So $E_0 \approx E_2$ to a very good level of approximation.
The only way that the value of $\Delta$ can be inferred is from analysis of nuclear reactions such as beta decay. So there was no way that physicists in the early 20th Century could know what value of $E_0$ to expect so that they could compare it with measured values of $E_2$.
