Bottomonia (October Post 2014)

Extensive experimental results at SPS (including feeddown from other less bound resonances like  ψ' and   χ_c) and RHIC of  J/ψ production in AA collisions clearly indicate that even the strong bound J/ψ ground state is suppressed.   

However at Large Hadron Collider(LHC) energies the J/ψ  production could be even enhanced due to the coalescence of un-correlated c-c_bar pairs in the medium which can cause a regeneration. Initial state effects like  modifications of the parton distribution functions in the nucleus relative to the nucleon (also known as shadowing) need to be taken in account. The final state effects like nuclear absorption are expected to be practically irrelevant at LHC energies. Studying the pA collisions at LHC energies is henceforth crucial to quantify the role of initial shadowing effects. On the otherhand the question arises if  J/ψ suppression or its absence is the final answer for QGP signature at collider energies.

At this point the study of bottomonia (Upsilon(1S), Upsilon(2S), Upsilon(3S)) candidates assumes importance. Since the Upsilon is smaller than the J/ψ , its absorption cross section should be smaller still. In terms of AA collisions, the Upsilon is expected to dissociate at a higher temperature than all the other quarkonium states, thus proving to be a more effective thermometer of the system. In addition, the smaller b-b_bar rate results in a lower probability for production by coalescence.