Summary
A systematic study has been carried out at various multiplicities onH-like andN-like interactions produced by 6.1 GeV/c mesons from the CERN P.S. in the École Polytechnique Heavy-Liquid Bubble Chamber, filled with a mixture of propane and CF3Br. The total multiplicity of events has been obtained by determining the number of neutral pions emitted, from measurements of the γ-rays materializing into the chamber and with the help of kinematics fit. Our results on the population of events in the various categories and on the angular and invariant mass distributions have been compared with the predictions of the existing models of high-energy interactions. While these results were, found to be in excellent agreement with the statistical model for events with six or more emitted pions, a strong contribution by peripheral processes exists at lower multiplicities. In addition to the one-pion exchange mechanism a contribution of ρ exchange, and Drell and Hiida diffraction seem relevant for events with pion multiplicity equal to two. “Nuclear” interactions, where the complex nucleus acts coherently, are present at all multiplicities up to five; this effect is particularly strong in the reactions where three pions are emitted. A bump between 1600 and 1800 MeV appears in the mass distribution of the events with four emitted pions. The values of the average transverse momenta of the secondaries at various multiplicities are reported.
Riassunto
Vengono riportati i risultati ottenuti in uno studio sistematico delle interazioni di π− da 6.1 GeV/c nella camera a bolle BP3 dell'École Polytechnique, riempita di una miscela di propano e freon. La molteplicità dei vari eventi viene stabilita in base al numero di mesoni π carichi e neutri, emessi nell'interazione. I dati sperimentali (sezioni d'urto distribuzioni angolari e di masse invarianti) sono confrontati con le predizioni dei vari modelli di interazione ad alte energie. Mentre gli eventi con sei o più pioni pioni emessi danno risultati in accordo con il modello statistico, gli eventi di molteplicità più bassa rivelano un forte contributo di processi periferici. In particolare nella molteplicità pionica due si osserva un contributo di O.P.E. e di modelli a due centri con scambio di ρ, oltre alla diffrazione del tipo Drell e Hiida. Nelle molteplicità minori di cinque si ha una forte presenza di interazioni nelle quali il nucleo rimane coerente; questo fenomeno risulta particolarmente importante nelle interazioni con tre pioni emessi. Negli eventi con molteplicità pionica uguale a quattro la massa invariante del sistema a quattro pioni carichi (2π+2π−) presenta un picco fra i 1600 ed i 1800 MeV/c2. Infine vengono riportati i valori degli impulsi trasversi dei secondari alle varie molteplicità.
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Bellini, G., di Corato, M., Duimio, F. et al. A study of 6.1 GeV/c π− interactions in a heavy-liquid bubble chamber. Nuovo Cimento A (1965-1970) 40, 948–978 (1965). https://doi.org/10.1007/BF02855997
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DOI: https://doi.org/10.1007/BF02855997