Magnetic field-induced anisotropic interaction in heavy quark bound states

Abstract

We have investigated how a strong magnetic field (B) could decipher the anisotropic interaction in heavy quark ($Q$) and antiquark ($\bar Q$) bound states through the perturbative thermal QCD in real-time formalism. So we thermalize Schwinger propagator for quarks in LLL and the Feynman propagator for gluons to calculate the gluon self-energy. For the quark-loop contribution to the self-energy, the medium does not have any temperature correction and the vacuum term gives rise an anisotropic term whereas the gluon-loop yields temperature correction. This finding in quark-loop contribution corroborates the equivalence of a massless QED in (1+1)-dimension with the massless thermal QCD in strong B, which (quark sector) is reduced to (1+1)-dimension (longitudinal). Thus the permittivity of the medium behaves like as a tensor. Thus the permittivity of medium makes the $Q \bar Q$ potential anisotropic, which resembles with a contemporary results found in lattice studies. As a result, potential for $Q \bar Q$-pairs aligned transverse to B is more attractive than parallel alignment. However, potential is always more attractive compared to B=0 due to softening of screening mass. However, the imaginary-part of potential becomes smaller compared to B=0. We have next investigated the effects of strong ${\bf B}$ on binding energies (B.E.) and thermal widths ($\Gamma$) of ground states of $c \bar c$ and $b \bar b$ in a time-independent perturbation theory, where binding energies gets increased and widths gets decreased, compared to $B =0$. Finally we have studied the quasi-free dissociation of bound states in a strong B. The dissociation temperatures estimated for $J/\psi$ and $\Upsilon$ states are obtained as $1.59 \rm{T_c} $ and $2.22 \rm{T_c}$, respectively, which are higher than the estimate in B=0 , thus preventing early dissolution of $Q \bar Q$ bound states.