Summary
Adopting five representative models so far proposed to explain the anomalous ℓ+ℓ−γ events,i.e. I) Z0→S or P+γ→ℓ+ℓ−γ, II) Z0→Z0 virt+γ→ℓ+ℓ−γ (anomalous magnetic-moment interaction), III)\(Z^0 \to \overline \ell \ell ^* + \ell \overline \ell ^* \to \ell ^ + \ell ^ - \gamma \) (excited lepton), IV) S or P→Z 0virt +γ→ℓ+ℓ−γ and V) standard bremsstrahlung, we study to what extent the lepton universality in these anomalous events is affected by finite lepton mass effects. We show that the lepton universality is very well satisfied in models I, II and IV, while very strongly violated in model III and moderately in model V. If combined with our previous study on the angular distributions and with the data, our present study would indicate that only the standard bremsstrahlung mechanism could survive.
Riassunto
Adottando cinque modelli rappresentativi proposti finora per spiegare gli eventi anomali ℓ+ℓ−γ, cioè I) Z0→S o P+γ→ℓ+ℓ−γ, II) Z0→Z 0virt +γ→ℓ+ℓ−γ (interazione ad impulso magnetico anomalo), III)\(Z^0 \to \overline \ell \ell ^* + \ell \overline \ell ^* \to \ell ^ + \ell ^ - \gamma \) (leptone eccitato), IV) S o P→Z 0virt +γ→ℓ+ℓ−γ e V) bremmsstrahlung, si studia in che maniera l’universalità leptonica in questi eventi anomali sia condizionata da effetti di massa leptonica finita. Si mostra che l’universalità leptonica non è soddisfatta nei modelli I, II e IV, mentre è violata fortemente nel modello III e moderatamente nel modello V. Se si combina con lo studio precedente sulle distribuzioni angolari e con i dati, questo studio indicherebbe che solo il meccanismo standard di bremsstrahlung potrebbe sopravvivere.
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Work supported by the US Department of Energy, contract DE-AC03-76SF00515.
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Hayashi, M., Katsuura, K. Lepton universality in anomalous ℓ+ℓ−γ events. Nuov Cim A 88, 44–52 (1985). https://doi.org/10.1007/BF02904248
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DOI: https://doi.org/10.1007/BF02904248