Summary
The reaction\(\pi ^ - + p \to e^ + + e^ - + n\) has been studied for values of the total c.m. energies ranging from 1.1 to 1.5 GeV. The «transverse» and «longitudinal» parts of the cross-section have been analysed in a particular kinematical configuration, where the neutron in the\(\pi ^ - - p\) c.m. system is at rest. This «quasi-threshold» condition has been selected in order to investigate the possibility of evaluating the nucleon form factors in the timelike region. In fact it turns out that the non-Born contributions, calculated on the basis of a simple model from pion photoproduction multipoles, do not exceed 20% of the corresponding contributions coming from the Born terms only in the energy range considered.
Riassunto
Si studia la reazione\(\pi ^ - + p \to e^ + + e^ - + n\) tra 1.1 e 1.5 GeV di energia totale nel centro di massa. Si analizzano le parti «trasversali» e «longitudinali» della sezione d'urto in una configurazione cinematica particolare, dove il neutrone è fermo nel sistema del baricentro pione-protone. Questa condizione di «quasi-soglia» è scelta per esplorare la possibilità di determinare i fattori di forma elettromagnetici dei nucleoni per valori tipo tempo del momento trasferito. Usando un semplice modello, che fa uso dei multipoli della fotoproduzione di pioni, per la stima dei contributi da aggiungere ai termini di Born, si trova che questi ammontano al massimo al 20% rispetto a quelli che si ottengono con i semplici termini di Born, nell'intervalo di energia qui considerato.
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Bietti, A., Petrarca, S. The reaction\(\pi ^ - + p \to e^ + + e^ - + n\): a possible source of information on the nucleon electromagnetic form factors in the timelike region: a possible source of information on the nucleon electromagnetic form factors in the timelike region. Nuov Cim A 22, 595–608 (1974). https://doi.org/10.1007/BF02804841
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DOI: https://doi.org/10.1007/BF02804841