  A first measurement of the longitudinal beam spin asymmetry ALU in the
semi-inclusive electroproduction of pairs of charged pions is reported. ALU 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 sin(phiR) moments of ALU are
extracted for the kinematic variables of interest in the valence quark region.
The understanding of di-hadron production is essential for the interpretation
of observables in single hadron production in semi-inclusive DIS, and
pioneering measurements of single spin asymmetries in di-hadron production open
a new avenue in studies of QCD dynamics.
