Heavy lepton pair production in nucleus-nucleus collisions at LHC energy - a case study

We present a study of $τ^{+}τ^{-}$ lepton pair production in Pb+Pb collisions at $\sqrt{s_{NN}}$ = 5.5 TeV. The larger $τ^{\pm}$ mass ($\sim$ 1.77 GeV) compared to $e^{\pm}$ and $μ^{\pm}$ leads to considerably small hadronic contribution to the $τ^{+}τ^{-}$ pair invariant mass ($M$) distribution relative to the production from thermal partonic sources. The quark-anti-quark annihilation processes via intermediary virtual photon, Z and Higgs bosons have been considered for the production of $τ^{+}τ^{-}$. We observe that the contribution from Drell-Yan process dominates over thermal yield for $τ^{+}τ^{-}$ pair mass from 4 to 20 GeV at the LHC energy. We also present the ratio of $τ$ lepton pair yields for nucleus-nucleus collisions relative to yields from p+p collisions scaled by number of binary collisions at LHC energies as a function $τ$ pair mass. The ratio is found to be significantly above unity for the mass range 4 to 6 GeV. This indicates the possibility of detecting $τ^{+}τ^{-}$ pair from quark gluon plasma (QGP) in the mass window $4\leq M$(GeV)$\leq 6$.

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