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Z -> b b-bar Excess from R-Parity Violation

David E. Brahm
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Abstract

The $\Zbb$ excess, $\Zcc$ deficit, and low left-right asymmetry $A_b$ may be explained by a single term $\lam C^c B^c B^{\prime c}$ in the superpotential. This operator violates R-parity and requires a sequential 4th generation. 1-loop diagrams involving squark exchange interfere with the tree-level processes to give an excess of right-handed $b$ quarks, and a deficit of right-handed $c$ quarks. Though the coupling must be large ($\lam\approx 2$ or $3$), the model is phenomenologically and cosmologically acceptable.

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David E. Brahm. 1996-08-22. Z -> b b-bar Excess from R-Parity Violation. https://arxiv.org/abs/hep-ph/9604325

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