The hard-to-observe W quickly decays into an electron and its matching antineutrino. The subatomic reaction shown immediately above depicts the process as it was first understood, in the first half of the 20th century. The boson ( W ) vanished so quickly that it was not detected until much later. Later, beta decay was understood to occur by the emission of a weak boson ( W ), sometimes called a charged weak current. Beta decay specifically involves the emission of a W boson from one of the down quarks hidden within the neutron, thereby converting the down quark into an up quark and consequently the neutron into a proton. The following diagram gives a summary sketch of the beta decay process according to the present level of understanding.