With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: South East England is the most populous and third largest region in England.
text_B: In particle physics , a resonance is the peak located around a certain energy found in differential cross sections of scattering experiments .. particle physics. particle physics. scattering experiments. scattering. These peaks are associated with subatomic particles , which include a variety of bosons , quarks and hadrons -LRB- such as nucleons , delta baryons or upsilon mesons -RRB- and their excitations .. excitations. excited state. In common usage , `` resonance '' only describes particles with very short lifetimes , mostly high-energy hadrons existing for or less .. The width of the resonance is related to the mean lifetime of the particle -LRB- or its excited state -RRB- by the relation. lifetime. mean lifetime. width of the resonance. resonance width. mean lifetime. mean lifetime. where h is the Planck constant and .. Planck constant. Planck constant. Thus , the lifetime of a particle is the direct inverse of the particle 's resonance width .. lifetime. mean lifetime. inverse. multiplicative inverse. second. For example , the charged pion has the second-longest lifetime of any meson , at .. lifetime. mean lifetime. second. second. pion. pion. Therefore , its resonance width is very small , about or about 6.11 MHz .. MHz. megahertz. Pions are generally not considered as `` resonances '' .. The charged rho meson has a very short lifetime , about .. lifetime. mean lifetime. rho meson. rho meson. Correspondingly , its resonance width is very large , at 149.1 MeV or about 36 ZHz .. MeV. megaelectronvolt. ZHz. zettahertz. This amounts to nearly one-fifth of the particle 's rest mass .. second. rest mass. rest mass
not_related.