Dissociation of heavy quarkonia in a weak magnetic field

Abstract

We examined the effects of the weak magnetic field on the properties of heavy quarkonia immersed in a thermal medium of quarks and gluons and studied how the magnetic field affects the quasifree dissociation of quarkonia in the aforementioned medium. For that purpose, we have revisited the general structure of gluon self-energy tensor in the presence of a weak magnetic field in thermal medium and obtained the relevant structure functions using the imaginary-time formalism. The structure functions give rise to the real and imaginary parts of the resummed gluon propagator, which further give the real and imaginary parts of the dielectric permittivity. The real and imaginary parts of the dielectric permittivity will be used to evaluate the real and imaginary parts of the complex heavy quark potential. We have observed that the real part of the potential is found to be more screened, whereas the magnitude of the imaginary part of the potential gets increased on increasing the value of both temperature and magnetic field. In addition to this, we have observed that the real part gets slightly more screened while the imaginary part gets increased in the presence of a weak magnetic field as compared to their counterparts in the absence of a magnetic field (pure thermal). The increase in the screening of the real part of the potential leads to the decrease of binding energies of $J/\mathrm{\ensuremath{\Psi}}$ and $\mathrm{\ensuremath{\Upsilon}}$, whereas the increase in the magnitude of the imaginary part leads to the increase of thermal width with the temperature and magnetic field both. Also the binding energy and thermal width in the presence of a weak magnetic field become smaller and larger, respectively, as compared to that in the pure thermal case. With the observations of binding energy and thermal width in hand, we have finally obtained the dissociation temperatures for $J/\mathrm{\ensuremath{\Psi}}$ and $\mathrm{\ensuremath{\Upsilon}}$, which become slightly lower in the presence of a weak magnetic field. For example, with $eB=0{m}_{\ensuremath{\pi}}^{2}$ the $J/\ensuremath{\psi}$ and $\mathrm{\ensuremath{\Upsilon}}$ are dissociated at $1.80{T}_{c}$ and $3.50{T}_{c}$, respectively, whereas with $eB=0.5{m}_{\ensuremath{\pi}}^{2}$ they dissociated at slightly lower values $1.74{T}_{c}$ and $3.43{T}_{c}$, respectively. This observation leads to the slightly early dissociation of quarkonia because of the presence of a weak magnetic field.