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

Abstract

We present a study of ${\tau }^{+}{\tau }^{-}$ lepton pair production in Pb + Pb collisions at $\sqrt{s_{\mathit{NN}}}=5.5\text{TeV}$. The larger ${\tau }^{\pm }$ mass (∼1.77 GeV) compared to $e^{\pm }$ and ${\mu }^{\pm }$ leads to considerably small hadronic contribution to the ${\tau }^{+}{\tau }^{-}$ 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 ${\tau }^{+}{\tau }^{-}$. We observe that the contribution from Drell–Yan process dominates over thermal yield for ${\tau }^{+}{\tau }^{-}$ 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 ${\tau }^{+}{\tau }^{-}$ pair from quark–gluon plasma (QGP) in the mass window $4⩽M\text{(GeV)}⩽6$.