Summary
Recognizing that present information on pion-nucleon scattering in the range (300÷1500) MeV is insufficient for a complete and unambigous analysis in terms of angular-momentum amplitudes, a study has been made employing restrictive assumptions related to the higher resonances. The π-p angular distribution data are found consistent with resonances of (T,J)=(1/2,3/2−) and (1/2,5/2+) at 600 and 900 MeV. A plausible, but nonunique, set of amplitudes has been determined, and the only significant departure from a simple behaviour is in the amplitude for the (1/2,1/2+) state, which could contain a resonance at 900 MeV. The Λ0K0 production cross-section shows features in agreement with such a resonance. A proposed phenomenological model based on the important role of the (3/2,3/2+) pion-nucleon state predicts the existence of eight resonances below 1500 MeV. Present experimental results are compared with the model and suggestions are made regarding possible tests.
Riassunto
Avendo riconosciuto che le attuali cognizioni sullo scattering pione-nucleone nel campo (300÷1500) MeV sono insufficienti per un’analisi completa e priva di ambiguità in termini delle ampiezze del momento angolare, si è fatto uno studio introducendo ipotesi restrittive relative alle risonanze più elevate. Si è trovato che i dati della distribuzione angolare π-p sono in accordo con risonanze di (T, J)=(1/2,3/2−) e (1/2, 5/2+) a 600 e 900 MeV. Si è determinato un gruppo di ampiezze plausibili, ma non unico, e la sola discordanza significativa è nell’ampiezza dello stato (1/2,1/2+), che potrebbe contenere una risonanza a 900 MeV. La sezione d’urto per la produzione Λ0K0 presenta caratteristiche corrispondenti a questa risonanza. Si propone un modello fenomenologico basato sul ruolo importante dello stato pione-nucleone (3/2,3/2+), che predice l’esistenza di otto risonanze al di sotto di 1500 MeV. Si confrontano gli attuali risultati sperimentali col modello e si suggeriscono possibili verifiche.
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Layson, W.M. Interpretation of pion-nucleon scattering results in the resonance region. Nuovo Cim 27, 724–747 (1963). https://doi.org/10.1007/BF02784577
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DOI: https://doi.org/10.1007/BF02784577