In particle physics, a resonance is the peak located around a certain energy found in differential cross sections of scattering experiments.
These peaks are associated with subatomic particles, which include a variety of bosons, quarks and hadrons (such as nucleons, delta baryons or upsilon mesons) and their excitations.
In common usage, "resonance" only describes particles with very short lifetimes, mostly high-energy hadrons existing for 10−23 seconds or less.
For example, the charged pion has the second-longest lifetime of any meson, at 2.6033×10−8 s.[2] Therefore, its resonance width is very small, about 2.528×10−8 eV or about 6.11 MHz.
The charged rho meson has a very short lifetime, about 4.41×10−24 s. Correspondingly, its resonance width is very large, at 149.1 MeV or about 36 ZHz.