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22–26 Sep 2025
Asia/Shanghai timezone

Nucleon 3D intrinsic spin structure from the weak-neutral axial-vector form factors

Not scheduled
3h 30m
Oral Three-dimensional structure of the nucleon: generalized parton distributions and form factors Parallel

Speaker

Dr Yi Chen (Tsinghua University & University of Science and Technology of China)

Description

We present the first systematic study of the relativistic intrinsic spin structure of a general spin-$1/2$ hadron in position space. We show in particular that the slope of the nucleon axial form factor $G_A^Z(Q^2)$ in the forward limit, conventionally denoted as $R^2_A \equiv -\frac{6}{G_A^Z(0) } \frac{ \text{d} G_A^Z(Q^2) }{\text{d} Q^2} \Big|_{Q^2=0} $ in the literature, does not faithfully characterize the size of the weak axial charge content of the nucleon in the Breit frame, but corresponds instead to a contribution to the nucleon 3D spin radius $r_\text{spin} \equiv \sqrt{\langle r_\text{spin}^2 \rangle}$, with $\langle r_\text{spin}^2 \rangle = R_A^2 + \frac{1}{4M^2}\left( 1 + \frac{G_P^Z(0)}{G_A^Z(0) } \right)$. We derive explicit expressions for the spin radius in different frames, and find in general additional contributions that depend on both the nucleon mass and the forward values of the axial-vector form factors $G_A^Z(0)$ and $G_P^Z(0)$. We also show that the second-class current contribution associated with the induced pseudo-tensor form factor $G_T^Z(Q^2)$ does not contribute in fact to both the nucleon axial and spin radii. Our work paves a new and direct way for investigating the nucleon 3D intrinsic spin structures using the weak-neutral axial-vector form factors $G_{A,P,T}^Z(Q^2)$ extracted from elastic (anti)neutrino-nucleon scattering data, or calculated in lattice QCD and various models and approaches.

Primary authors

Prof. Cédric Lorcé (CPHT, CNRS, Ecole polytechnique, Institut Polytechnique de Paris, 91120 Palaiseau, France) Yang Li (University of Science and Technology of China) Dr Yi Chen (Tsinghua University & University of Science and Technology of China) Qun Wang (University of Science and Technology of China)

Presentation materials

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