Beam Single-Spin Asymmetry in Semi-Inclusive Deep Inelastic Scattering

TL;DR

The paper investigates beam single-spin asymmetries in semi-inclusive jet production within a quark–diquark model, showing that final-state interactions generate a $T$-odd observable $A_{LU}^{\sin\phi}$ that scales as $1/Q$ (twist-3). It derives explicit expressions via a gauge-invariant set of diagrams and connects the asymmetry to the TMD $g^\perp$, providing a model-based calculation of both $A_{LU}^{\sin\phi}$ and $g^\perp$. The results, including numerical plots for realistic parameters, yield asymmetries of a few percent, compatible with experimental observations, and highlight caveats related to factorization for twist-3 TMDs. The work also explores a scalar-quark version of the problem, showing the qualitative persistence of the effect across spin assignments. Overall, it reinforces the role of final-state interactions in generating beam spin asymmetries and offers a concrete framework linking observable asymmetries to initial-state TMDs.

Abstract

We calculate, in a model, the beam spin asymmetry in semi-inclusive jet production in deep inelastic scattering. This twist-3, $T$-odd observable is non-zero due to final state strong interactions. With reasonable choices for the parameters, one finds an asymmetry of several percent, about the size seen experimentally. We present the result both as an explicit asymmetry calculation and as a model calculation of the new transverse-momentum dependent distribution function $g^\perp$.

Figures (6)

• Figure 1: Lowest order graphs.
• Figure 2: One-loop graphs that have imaginary parts.
• Figure 3: Beam single spin asymmetry for quark jets of different flavors and beam energy of 4.25 GeV. Data are from Ref.Avakian:2003pk. See the text for notation.
• Figure 4: Beam single spin asymmetry for quark jets of different flavors and beam energy of 5.7 GeV. Data are from Ref.Avakian:2003pk. Notation is as in Fig.\ref{['fig:4.25gev']}.
• Figure 5: Beam single spin asymmetry for quark jets of different flavors and beam energy of 27.5 GeV. Also shown are preliminary data from HERMES hermes_ssa. Notation is as in Fig.\ref{['fig:4.25gev']}.