Single spin asymmetry $ A _{ U L } ^ { \sin ( 2 \phi _ { h } ) }$ in dihadron production in SIDIS

TL;DR

This paper calculates the helicity-dependent dihadron fragmentation function using a spectator model to understand the weak single spin asymmetry observed in SIDIS, providing theoretical predictions and insights into the asymmetry's origin.

Contribution

It introduces a calculation of the T-odd dihadron fragmentation function within a spectator model and explains the small observed asymmetry without relying on transverse momentum dependent factorization.

Findings

Calculated the $A_{UL}^{ ext{sin}(2 heta_h)}$ asymmetry in SIDIS.

Predicted asymmetry values for HERMES and EIC experiments.

Provided theoretical explanation for the weak asymmetry signal.

Abstract

The paper calculates the helicity-dependent dihadron fragmentation function (DiFF), by extending the dihadron spectator model and examine the single longitudinal spin asymmetry $A^{\sin(2\phi_h)}_{UL}$ from dihadron in semi-inclusive inelastic scattering (SIDIS). This function elucidates the relationship between the longitudinal polarization of the fragmented quark and the transverse momentum of the resulting hadron pairs. A study by the COMPASS collaboration detected a minimal signal in their experimental search for this azimuthal asymmetry in SIDIS. Here, we use the spectator model to calculate the unknown T-odd dihadron fragmentation function $H_1^\perp$. Adopting collinear factorization to describe the data, avoiding the transverse momentum dependent factorization and the associated resummation effects, helping us understand the asymmetry and explaining why the signal is so weak. We involve the approach of transverse momentum dependence in the model calculations, in order to formulate the differential cross sections and the spin asymmetries in terms of the collinear parton distributions and the collinear DiFFs. A transverse momentum factor analysis method was used, in which the transverse momentum of the final hadron pairs was not integrated. The asymmetry of $sin(2\phi_h)$ in COMPASS kinematics was calculated and compared with experimental data. In addition, predictions for the same asymmetry are also presented for HERMES and the Electron Ion Collider.