One Bit per Weak Decay

We show that maximal parity violation in the weak interaction has a precise information-theoretic characterization: each weak decay emitting a single neutrino—and preserving the hadronic spin—produces exactly ln 2 nats = 1 bit of spin-state entropy. We verify this across 16 decay channels spanning all quark flavors, from neutron beta decay to B-meson semileptonic decay, and show that pure leptonic decays (two neutrinos emitted) produce exactly zero bits. We argue that this result reflects a deeper structure: maximal parity violation is a projection operation on the neutrino's helicity qubit, converting a quantum degree of freedom into a classical one. The projection interpretation predicts that any departure from maximal parity violation would reduce the entropy yield below 1 bit (quantified by the Shannon entropy of the helicity distribution), and that the neutrino's spin-1/2 nature is the unique choice producing integer-bit accounting. This characterization yields a testable consequence for neutrinoless double beta decay (0νββ): the process requires a two-bit structural change without emitting any neutrinos to carry the information away. We interpret the strong experimental suppression of 0νββ as consistent with the high cost of "receiptless" information deletion, and note a structural parallel with the black hole information problem, where Hawking radiation plays the analogous role of informational receipt.