Protontoneutron

Protontoneutron is a term used in theoretical discussions to denote a transient, hypothetical bound state consisting of a proton and a neutron. In this context it is sometimes described as a dibaryon-like resonance that could arise in high-energy or high-density nuclear environments. It is not recognized as a stable particle within the standard model and is distinct from the deuteron, which is a stable nucleus.

Its proposed properties depend on the specific quantum configuration. If it exists, it would carry a net electric charge of +1 and would have a mass close to the sum of the proton and neutron masses minus a small binding energy. Spin, parity, and isospin would be determined by the coupling of the nucleons, and the state would be expected to be very short-lived, decaying via strong or electromagnetic processes into lighter hadrons, such as a deuteron with emission of a photon or a charged pion, or by dissociation into a free proton and neutron.

Formation and decay: Several production mechanisms have been proposed, including high-energy nucleon-nucleon collisions and near-threshold resonant formation in deuteron channels. In scattering experiments it would appear as a resonance or enhancement in the proton-neutron channel, with a characteristic invariant-mass or missing-mass signature indicating a transient bound state.

Theoretical status and experiments: The existence of dibaryon-like states beyond the deuteron has been a topic of debate in nuclear physics. Some models and lattice QCD studies have examined the possibility of protontoneutron states, but no conclusive experimental evidence has been established. Ongoing and planned experiments in nucleon-nucleon scattering and heavy-ion collisions aim to constrain production rates and search for resonant signals.

See also: deuteron, dibaryon, H-dibaryon, nucleon-nucleon interaction.