A carbon-11 nucleus decays via β+\beta^+β+ decay into a boron-11 nucleus, emitting a positron and an unknown particle YYY:
611C→511B+β++Y^{11}_{6}\text{C} \rightarrow ^{11}_{5}\text{B} + \beta^+ + Y611C→511B+β++Y
What is the identity of particle YYY?
electron antineutrino
electron neutrino
neutron
gamma photon