Neutrinos and antineutrinos

Beta decay does not emit a beta particle on its own. Each decay also emits a neutrino or an antineutrino:

• beta-minus decay produces an electron antineutrino, written $\bar{\nu}_e$;
• beta-plus decay produces an electron neutrino, written $\nu_e$.

The complete equations are

$\text{n} \rightarrow \text{p} + \text{e}^- + \bar{\nu}_e \qquad\qquad \text{p} \rightarrow \text{n} + \text{e}^+ + \nu_e$

or, in nuclide notation, for example

$^{14}_{6}\text{C} \rightarrow {}^{14}_{7}\text{N} + {}^{0}_{-1}\text{e} + \bar{\nu}_e \qquad\qquad {}^{22}_{11}\text{Na} \rightarrow {}^{22}_{10}\text{Ne} + {}^{0}_{+1}\text{e} + \nu_e$

Because it has no charge and essentially no mass, a neutrino barely interacts with matter: it can pass through the Earth without being stopped. That is why it went undetected for decades after its existence was predicted.

Nucleon number conservation is unaffected by the neutrino, since its $A$ is 0. Its zero charge means your charge balance is also unaffected. It shows up in the equation because energy and momentum must balance.