Summary
The reactionN(γ, ρ0)N is remarked as unique in having practically no allowed one-boson exchange processes, so that it serves as a sort of “laboratory” for studying two-boson (pion) exchange. The two-pion term can be evaluated absolutely and is estimated crudely for larges and smallt; it is found to account well for a couple of measured forward cross-sections. The forms are different from those of the diffraction treatment: No one-pion exchange need be invoked, and the ρ0 is polarized transverse to the incident beam only for θ=0o; at finite angles the ρ0 has a component parallel to the incident direction. For small angles and high energies this component represents transverse polarization of the ρ0 relative to its own direction of motion.
Riassunto
Si osserva che la reazioneN(γ, ρ0)N è la sola a non avere praticamente processi a scambio di un bosone consentiti, così che serve come una specie di “laboratorio” per studiare lo scambio di due bosoni (pioni). Il termine di due pioni può essere valutato in forma assoluta e se ne fa una stima grossolana pers grande et piccolo; si trova che rende conto in modo soddisfacente di alcune sezioni d’urto anteriori misurate. Le formule sono differenti da quelle del trattamento di diffrazione: non occorre invocare alcuno scambio di un pione, e il γ0 è polarizzato trasversalmente al fascio incidente solo per θ=0o; per angoli finiti il ρ0 ha una componente parallela alla direzione di incidenza. Per piccoli angoli e alte energie questa componente rappresenta la polarizzazione trasversale del ρ0 relativa alla sua direzione di moto.
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References
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Peaslee, D.C. (γ, ρ0) as two-pion exchange. Nuovo Cimento A (1965-1970) 44, 784–793 (1966). https://doi.org/10.1007/BF02911204
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DOI: https://doi.org/10.1007/BF02911204