Speaker
Description
Hard exclusive single-pion electroproduction off the proton gives complementary access to the three-dimensional partonic structure of the
nucleon in two distinct kinematic regimes. In the forward region (small
$|t|$), collinear QCD factorization relates the amplitude to generalized
parton distributions (GPDs). For pseudoscalar mesons the transverse-photon response observed at CLAS and CLAS12 is particularly sensitive to the chiral-odd (transversity) GPDs $H_T$ and $\bar{E}_T$ within the Goloskokov--Kroll framework, while the $\pi^+$ channel additionally probes $\tilde{H}$ and the pion-pole $\tilde{E}$. In the backward region (small $|u|$), a conjectured factorization relates the amplitude to nucleon distribution amplitudes and baryon-to-meson transition distribution amplitudes ($\pi N$ TDAs), which encode the quark-momentum and spin correlations linking the nucleon to the pion. I will present recent $\pi^0$ and $\pi^+$ measurements from CLAS and CLAS12 at Jefferson Lab --- structure functions and beam-spin asymmetries in both the forward (GPD) and backward (TDA) regimes --- and discuss their interpretation and the prospects opened by the full 12~GeV dataset.