A first measurement of the longitudinal beam spin asymmetry $A_{LU}$ in the semi-inclusive electroproduction of pairs of charged pions is reported. $A_{LU}$ is a higher-twist observable and offers the cleanest access to the nucleon twist-3 parton distribution function $e(x)$. Data have been collected in the Hall-B at Jefferson Lab by impinging a 5.498-GeV electron beam on a liquid-hydrogen target, and reconstructing the scattered electron and the pion pair with the CLAS detector. One-dimensional projections of the $A_{LU}^{\sin {\varphi }_R}$ moments are extracted for the kinematic variables of interest in the valence quark region. The understanding of dihadron production is essential for the interpretation of observables in single-hadron production in semi-inclusive DIS, and pioneering measurements of single-spin asymmetries in dihadron production open a new avenue in studies of QCD dynamics.

• Received 26 October 2020
• Revised 23 December 2020
• Accepted 12 January 2021

DOI:https://doi.org/10.1103/PhysRevLett.126.062002

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Published by the American Physical Society