Thermal Spectrum of Heavy Vector and Axial Vector Mesons in the Framework of QCD Sum Rules Method

The masses and the leptonic decay constants of vector and axial vector heavy-heavy mesons are calculated using the thermal QCD sum rules approach. While obtaining the QCD sum rules, additional operators in the Wilson expansion and also temperature dependency of the continuum threshold are taken into account. The masses and the decay constants remained unchanged up to $T\simeq100~MeV$. After that point, they start to diminish. At the critical temperature, the masses decreased about $3\%$, $5\%$ and $14\%$ for the vector mesons $\Upsilon$, $B_{c}$ and $J/\psi$; $6\%$, $7\%$ and $22\%$ for the axial vector mesons $\chi_{b1}$, $B_{c}$ and $\chi_{c1}$, respectively. The decay constants reached about less than $20\%$ of their vacuum values. The obtained results of the thermal mass and decay constant calculations at zero temperature are in a very good agreement with the other non-perturbative calculations at vacuum as well as with the experimental data.