Il Nuovo Cimento A (1965-1970)

, Volume 47, Issue 2, pp 232–251 | Cite as

Production of\({\mathcal{N}}^* (1518)\) and\({\mathcal{N}}^* (1688)\) isobars in\(\bar pp\) interactions at 5.7 GeV/c. Determination of their widths and decay branching ratiosinteractions at 5.7 GeV/c. Determination of their widths and decay branching ratios

  • V. Alles-Borelli
  • B. French
  • Å. Frisk
  • L. Michejda


The nucleon isobars\({\mathcal{N}}^* (1518)\) and\({\mathcal{N}}^* (1688)\) are observed in inelastic interactions of 5.7 GeV/c antiprotons in hydrogen. The widths of both of them are found to be small ((55±15) MeV and (70±20) MeV respectively), in agreement with recent phase-shift data. The 2-body to 3-body branching ratios are estimated (being 1.25 −0.71 +0.44 in the case of the\({\mathcal{N}}^* (1518)\) and less than 1.26 with 95% confidence for the\({\mathcal{N}}^* (1688)\) and show that the inelasticities of both resonances in πp scattering are high. A detailed study of the 3-body\({\mathcal{N}}\pi \pi \) decays provides no evidence in either case for the cascade decay into\(\mathcal{N}^* (1238) + \pi \). Deviations from uniform population of the Dalitz plots for the 3-body decays are observed and are studied in terms of the 3-body decay matrix elements. Upper limits for decay of the\({\mathcal{N}}^* (1688)\) into\({\mathcal{N}}\eta \) and ΛK final states are estimated.


Mass Distribution Decay Mode Interference Term Peak Region Dalitz Plot 
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Рождение\({\mathcal{N}}^* (1518)\) и\({\mathcal{N}}^* (1688)\) изобар в взаимодействиях\(\bar pp\) при 5.7 ГэB/c; определение их ширин и отношений тицоь распадапри 5.7 ГэB/c; определение их ширин и отношений тицоь распада


Наблюдаются нуклонные изобары\({\mathcal{N}}^* (1518)\) и\({\mathcal{N}}^* (1688)\) при неупругих взаимодействиях 5.7 ГэB/c антипротонов в водороде. Найдено, что их ширины малые, (55±15) MэB и (70±20) MэB, соответственно, что согласуется с недавними данными фазового анализа. Оцениваются отношения двух-частичных и трех-частичных распадов, причём, отношения равны 1.25 −0.71 +0.44 в случае\({\mathcal{N}}^* (1518)\) и меньше чем 1.26, c 95% уверенностью, для\({\mathcal{N}}^* (1688)\); показано, что неупругости обоих резонансов при πp рассеянии являются значительными. Детальное 3-частичных\({\mathcal{N}}\pi \pi \) распадов позволяет установить, что в любом случае не наблюдается каскадный распад в\(\mathcal{N}^* (1238) + \pi \). Наблюдаются отклонения от равномерной заселенности Далитцевских кривых для 3-частичных распадов и ⥹ти отклонения изучаются в выражениях матричных элементов 3-частичного распада. Оцениваются верхние пределы для распада\({\mathcal{N}}^* (1688)\) в\({\mathcal{N}}\eta \) и в ΛK в конечных состояниях.


Sono stati osservati gli isobari nucleonici\({\mathcal{N}}^* (1518)\) ed\({\mathcal{N}}^* (1688)\) nelle interazioni anelastiche di antiprotoni di 5.7 GeV/c in idrogeno. Sono state trovate come larghezze di questi isobari (55±15) MeV e (70±20) MeV rispettivamente, in accordo con i dati ottenuti recentemente dall'analisi in fasis. Sono stati stimati i rapporti di decadimento in 2 corpi ed in 3 corpi (1.25 −0.71 +0.44 per\(l'{\mathcal{N}}^* (1518)\) e minore di 1.26 con il 95% di attendibilità per\(l'{\mathcal{N}}^* (1688)\) e si è dimostrato che le anelasticità di entrambe le risonanze nello scattering πp sono alte. Uno studio dettagliato dei decadimenti in tre corpi\({\mathcal{N}}\pi \pi \) non dà evidenza in alcun caso per il decadimento a cascata in\(\mathcal{N}^* (1238) + \pi \). Nei diagrammi di Dalitz sono state osservate delle deviazioni dalla distribuzione uniforme degli eventi per i decadimenti in tre corpi e sono state studiate in termini di elementi della matrice di decadimento in tre corpi. Sono stati stimati i limiti superiori per i decadimenti\(dell'{\mathcal{N}}^* (1688)\) in\({\mathcal{N}}\eta \) e ΛK.


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Copyright information

© Società Italiana di Fisica 1967

Authors and Affiliations

  • V. Alles-Borelli
    • 1
  • B. French
    • 1
  • Å. Frisk
    • 1
  • L. Michejda
    • 1
  1. 1.CERNGeneva

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