112.1 Introduction The production of heavy quarkonia (bottomonium and charmonium) is modified in the heavy-ion collisions as compared with elementary nuclear collisions. This modification in the production of quarkonia is due to the hot and dense medium formed in heavy ion collisions named as Quark-Gluon Plasma (QGP) which is expected not to be produced in the elementary collisions. In such a thermalized medium, quarks and gluons can cause the dissociation of heavy mesons present in the medium. Likewise, bottomonium and charmonium present in the medium can be destroyed, but the constituent quarks (q) anti-quarks (q) will likely stay spatially correlated due to small mean free paths in this system. In the due course of time, they can recombine and form color neutral states. As charm quark and aniquarks have less mass than bottom quark-anti quarks, they can be present in the medium in sufficient numbers from the initial time of the QGP. These are called un-correlated cc pairs. These correlated as well as uncorrelated cc pair can recombine to form charmonium states (e.g., J/ψ, X_c, ψ). So, charmonium regeneration can happen in two ways, first one is through correlated cc and another is by un-correlated cc pair. But because of the very heavy mass, the number of uncorrelated bb pair would be too small. Thus, the possibility of the recombination of un-correlated bb pairs in the medium is negligible. That is why regeneration of bottomonium (normally due to un-correlated pairs) in QGP has been neglected so far. But regeneration of bottomonia due to correlated bb pair may be present in the medium which can play a significant role in explaining the bottomonium nuclear modification factor, R_(AA). Quarkonium suppression in a thermal QCD medium created in heavy ion collisions is a complex interplay of various physical processes, e.g., Gluonic dissociation, Collisional damping, Color screening and Cold Nuclear Effects [1-3]. Here we plan to describe the production of charmoniu
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