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A baryon is a hadron with half-integer spin and baryon number one. Ordinary valence baryons contain three quarks, whereas an antibaryon has opposite baryon number and conjugate valence content. The proton and neutron are the most familiar examples.

Three valence quarks do not fix every property: their flavor, spin coupling and orbital angular momentum distinguish different states. For example, a proton and a Delta-plus baryon both have $uud$ valence content but different spin and excitation energy. Gluonic and additional quark–antiquark contributions also belong to the interacting state, so adding three free-quark masses is not a complete baryon-mass calculation.

The Delta baryon ground multiplet is a short-lived baryon resonance family with isospin $3/2$ and spin-parity $3/2^{+}$. Its four charge states have ordinary valence contents $uuu$, $uud$, $udd$ and $ddd$, with charges $+2,+1,0,-1$ in elementary-charge units.

The familiar Delta-plus baryon and the proton share valence flavor content but differ in their spin coupling and mass. Strong decay into a nucleon and a pion gives the Delta resonance a broad decay width. In scattering, a resonance appears through an energy-dependent amplitude and cross section, not as an indefinitely stable additional constituent of every atomic nucleus.^[ref]

At time $t_0$, the accelerated proton has momentum $p=qE{t}_0$ and, by the relativistic energy-momentum relation, energyThe incident cosmic microwave background photon adds energy $E_{\gamma }$. Since the final state contains only the Delta-plus baryon, conservation of relativistic energy gives its laboratory-frame Lorentz factorIts rest-frame decay time $t_{\Delta }$ is a proper time, so time dilation gives the laboratory decay time