  Transverse Momentum Dependent (TMD) dihadron production, including vector
meson production, allows access to various TMD distribution and fragmentation
functions. Dihadron production is complementary to single hadron semi-inclusive
DIS measurements, pairing the same distribution functions with different
fragmentation functions. While dihadrons present unique measurement
opportunities, the TMD dihadron cross section is significantly more complex
than that for single hadron production, due to the polarization in the final
state. Various theoretical advances, which further clarify the complexity, will
be highlighted. The HERMES analysis of the transverse target moments of the TMD
dihadron cross section allows the first test of a particular prediction of the
Lund/Artru string fragmentation model, specifically that the favored Collins
fragmentation function has opposite sign in single hadron production versus
vector meson production. The status and results of this analysis will be
discussed and an extension of the Lund/Artru model for disfavored fragmentation
will also be presented.
