Single spin asymmetry in $e+p\to e'+B^\uparrow+X$

TL;DR

This work identifies and characterizes a naive-T-odd single-spin asymmetry in electron–proton scattering with a transversely polarized leading baryon in the target fragmentation region, focusing on the azimuthal correlation $\sin(\phi_{\ell'}-\phi_{s_B})$. It develops two complementary theoretical frameworks: (i) a collinear, high-$Q^2$ description based on twist-three T-odd fracture functions, yielding an $F_{\rm odd}$ term proportional to $x_B u_{TR}$, and (ii) a high-energy description via spin-dependent odderon exchange that generates the same asymmetry through Pomeron–odderon interference in diffractive DIS. The paper also discusses experimental prospects, notably recoil polarimetry for measuring the final-state baryon spin and potential SIDDIS channels, and provides crude estimates illustrating where the asymmetry could become observable. Overall, it connects historical ideas on final-state polarization with modern QCD formalisms, offering multiple avenues to probe spin phenomena in the target fragmentation region. The results highlight the relevance of both twist-three fracture-functions and odderon dynamics for understanding transverse spin effects beyond conventional current-fragmentation SSA studies.

Abstract

We study an exotic type of single spin asymmetry in unpolarized electron-proton scattering, in which the outgoing electron momentum exhibits a left-right asymmetry relative to the transverse spin of the leading baryon $B$ in the target fragmentation region. We lay out two theoretical frameworks for describing this effect: The twist-three fracture function at high-$Q^2$ and the spin-dependent odderon in the high energy limit.

Figures (2)

• Figure 1: Lowest order diagrams for the process $e+p\to e'+B^\uparrow+X$. The cross on the quark line represents the on-shell imaginary part.
• Figure 2: SSA $A_N$ (divided by the constant $C$) as a function of $z_f$ and $P_{h\perp}^2$.