“…Some of their properties are confirmed also by QCD sum rules [22,23] and an effective Lagrangian [20,[22][23][24]. In particular, there are some characteristic phenomena: (i) the mixing between spin-singlet and spin-triplet eigenstates [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33], which originates from the Zeeman coupling of charm quarks, (ii) the Landau levels of charm quarks (or squeezing of spatial wave function), (iii) anisotropic (or modified) confinement potential [18,[34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49], and (iv) the motional Stark effect (or Lorentz ionization) in moving charmonia [17,18,26,31,50,51]. For other phenomenological studies, see Refs.…”