New observables in longitudinal single-spin asymmetries in semi-inclusive DIS

TL;DR

The paper provides a complete twist-3, TMD-based framework for longitudinal beam and target single-spin asymmetries in SIDIS and jet DIS, revealing a new gauge-link–dependent pair of functions, $g^ op{}$ and $G^ op{}$, that contribute to $A_{LU}$ and $A_{UL}$. By incorporating the full correlator decomposition, including previously neglected terms, the authors derive gauge-invariant hadronic tensors and explicit expressions for asymmetries, showing how the new functions (along with $f_L^ op$ and related quantities) shape the observed angular modulations. The work highlights the importance of gauge-link direction in the decomposition of parton correlators and proposes experimental tests (notably jet-DIS measurements) to validate the existence of $g^ op{}$ and $G^ op{}$, with potential implications for resolving discrepancies with data such as $A_{UT}$. Overall, it advances the theoretical description of longitudinal spin phenomena in high-energy scattering and informs future phenomenology and experimental analyses.

Abstract

We analyze longitudinal beam and target single-spin asymmetries in semi-inclusive deep inelastic scattering and in jet deep inelastic scattering, including all possible twist-3 contributions as well as quark mass corrections. We take into account the path-ordered exponential in the soft correlators and show that it leads to the introduction of a new distribution and a new fragmentation function contributing to the asymmetries.