We find a novel phenomenon induced by the interplay between a strong magnetic
field and finite orbital angular momenta in hadronic systems, which is
analogous to the Paschen-Back effect observed in the field of atomic physics.
This effect allows the wave functions to drastically deform. We discuss
anisotropic decay from the deformation as a possibility to measure the strength
of the magnetic field in heavy-ion collision at LHC, RHIC and SPS, which has
not experimentally been measured. As an example we investigate charmonia with a
finite orbital angular momentum in a strong magnetic field. We calculate the
mass spectra and mixing rates. To obtain anisotropic wave functions, we apply
the cylindrical Gaussian expansion method, where the Gaussian bases to expand
the wave functions have different widths along transverse and longitudinal
directions in the cylindrical coordinate.Comment: 8 pages, 8 figures, v3: updated to the published style on PL