Charmonium spectral functions in vector and pseudoscalar channels at finite temperature are investigated through the complex Borel sum rules and the maximum entropy method. Our approach enables us to extract the peaks corresponding to the excited charmonia, ψ ′ and η c′ , as well as those of the ground states, J/ψ and η c , which has never been achieved in usual QCD sum rule analyses. We show the spectral functions in vacuum and their thermal modification around the critical temperature, which leads to the almost simultaneous melting (or peak disappearance) of the ground and excited states.
Araki, K. J., Suzuki, K., Gubler, P., & Oka, M. (2018). Charmonium ground and excited states at finite temperature from complex Borel sum rules. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 780, 48–53. https://doi.org/10.1016/j.physletb.2018.01.072