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A new evaluation of the pion weak form factors

Dinko Pocanic
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Abstract

We have used the PIBETA large acceptance detector for a precise measurement of the $π^+ \to e^+νγ$ radiative decay at rest, with broad phase space coverage. Using the CVC value for the pion vector form factor, $F_V = 0.0259(5)$, we have obtained a new value of the pion axial-vector form factor $γ= F_A/F_V = 0.429(14)$. However, significant deviations from the SM predictions are evident in our data. The discrepancy can be accounted for by introducing a pion tensor form factor of $F_T = -0.0016(3)$. The question of the true nature of the observed deviations remains open pending further theoretical and experimental study.

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Dinko Pocanic. 2003-11-06. A new evaluation of the pion weak form factors. https://arxiv.org/abs/hep-ex/0311013

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