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arXiv · 2407.21471

Pion polarizabilities from a dispersive analysis of $\gamma\gamma \to \pi\pi$

Viktoriia Ermolina·Igor Danilkin·Marc Vanderhaeghen
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Abstract

We present results for the charged and neutral pion polarizabilities, obtained through a dispersive analysis of photon-fusion reactions with two pions in the final state. This analysis is motivated by current and future measurements at COMPASS, JLab (Hall D), and the BESIII measurement of single-virtual photon-fusion reactions in the space-like region, offering insight into generalized pion polarizabilities. To improve predictions within an unsubtracted dispersion formalism with only the pion left-hand cut, one needs to consider the influence of heavier left-hand cuts. We parametrize the latter using an expansion in a suitably constructed conformal variable, capturing the analytical structure of the left-hand cuts. The coefficients in this expansion are determined from the matching with the Lagrangian-based approach, the Adler zero constraint for $\gamma\gamma \to \pi^0\pi^0$, and a fit to the cross-section data. The extension to the single-virtual case is also discussed.

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Viktoriia Ermolina, Igor Danilkin, Marc Vanderhaeghen. 2024-07-31. Pion polarizabilities from a dispersive analysis of $\gamma\gamma \to \pi\pi$. https://arxiv.org/abs/2407.21471

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