  Gluons inside unpolarized hadrons can be linearly polarized provided they
have a nonzero transverse momentum. The simplest and theoretically safest way
to probe this distribution of linearly polarized gluons is through cos(2 phi)
asymmetries in heavy quark pair or dijet production in electron-hadron
collisions. Future Electron-Ion Collider (EIC) or Large Hadron electron
Collider (LHeC) experiments are ideally suited for this purpose. Here we
estimate the maximum asymmetries for EIC kinematics.
