Summary
A study of inelastic n-p interactions has been made using the Birmingham 1 GeV synchrotron and a 9 in. diameter liquid hydrogen bubble chamber. 1840 three-pronged events initiated by neutrons in the energy range (290 ÷ 970) MeV have been analysed, the possible reactions being: n + p → p + p + π−; n + p → n + p + π0, π0 → e+ + e- + γ, and n + p → n + p + π+ + π−. The ratio found for the integrated cross-sections σ(n + p → n + p + π0) /σ (n + p → p + p + ρ-) = 2.67 ± 0.43 is shown to resolve a long-standing conflict with charge independence. The energy-dependence of the n + p → p + p + π− cross-section has been inferred from the expected shape of the incident neutron spectrum with the aid of earlier cross-section measurements in the energy range. The laboratory kinetic energy distributions and centre-of-mass angular distributions for protons from ppπ- events suggest that the peripheral mechanism of interaction is important at lower energies and to a greater extent than indicated by the one-pion-exchange model. However the Treiman-Yang test for this model is satisfied for events involving small momentum transfer and (3, 3) isobar production. The cross-section for the reaction n + p → n + p + π+ + π- increases more quickly above threshold than required by the statistical model of Cerulus and Hagedorn, and much more so than required by one-pion-exchange processes. Comparison with p-p scattering results, in which double-pion production is far smaller, emphasizes the importance of theT=0 channel.
Riassunto
Si è eseguito uno studio delle interazioni n-p anelastiche a mezzo del sincrotrone di 1 GeV di Birmingham e di una camera a bolle ad idrogeno liquido di 9 in. Si sono analizzati 1840 eventi a 3 rami iniziati da neutroni nell’intervallo di energia (290 ÷ 970) MeV; le reazioni possibili erano: n + p → p + p + π-; n + p → n + p + π0, π0 → e+ + e− + γ; n + p → n + p + π+ + π-. Si mostra che il rapporto trovato per le sezioni d’urto integrate σ(n + p → n + p + π0)/σ(n + p → p + p + π-) = 2.67 ± 0.43 risolve un eonflitto di vecchia data oon l’indipendenza délia carioa. Con l’aiuto di preoedenti misure délia sezione d’urto di questo intervallo di energia, dalla forma prevista dello spettro dei neutroni incidenti si É dedotta la dipendenza dell’energia délia sezione d’urto n + p-*-p+p + 7i~. Le distribuzioni dell’energia cinetica nel sistema del laboratorio e le distribuzioni angolari nel sistema del centro di massa dei protoni prodotti negli eventi ppπ- suggeriscono che il meccanismo di interazione periferico è importante alle energie più basse ed in misura maggiore di quanto è indieato dal modello con scambio di un pione. Tuttavia il criterio di Treiman-Yang per questo modello è soddisfatto per eventi ehe interessano un piccolo momento trasferito e la produzione di isobari (3, 3). La sezione d’urto della reazione n + p → n + p + π+ + π- cresce più rapidamente sopra la soglia di quanto è richiesto dal modello statistico di Cerulus e Hagedorn, ed ancor più di quanto richiesto da processi con scambio di un pione. Il confronto con i risultati dello scattering p-p, in oui la produzione di due pioni è molto inferiore, mette in rilievo l’importanza del canale T=0.
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On leave at Saclay, Gif sur Yvette.
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Rushbrooke, J.G., Bugg, D.V., Oxley, A.J. et al. Neutron-proton interactions in the energy range (290 ÷ 970) MeV. Nuovo Cim 33, 1509–1537 (1964). https://doi.org/10.1007/BF02749671
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DOI: https://doi.org/10.1007/BF02749671