Speaker
Description
A unified description of the transverse-momentum spectrum in semi-inclusive deep-inelastic scattering (SIDIS) requires consistent matching between the low-$P_{hT}$ TMD regime and the high-$P_{hT}$ collinear regime. While this is well established at leading power for unpolarized structure functions, discrepancies arise at subleading power, where contributions may be phenomenologically significant and impact the extraction of universal TMDs.
We present a systematic study of longitudinal photon contributions within a unified framework connecting these regimes. Analyzing their behavior across the matching region, where resummed TMD dynamics transitions to fixed-order collinear factorization, we quantify their impact on unpolarized cross sections. We further investigate the longitudinal structure function $F_{UU,L}$ and the ratio $R_{\mathrm{SIDIS}}=F_{UU,L}/F_{UU,T}$ as probes of subleading dynamics. Our results clarify subleading-power effects in matching and provide constraints for global TMD analyses.