Search for the lepton-flavour-violating decays $B^0\to K^{\ast 0}{\tau }^{\pm }{e}^{\mp }$

A first search for the lepton-flavour-violating decays $B^0\to K^{\ast 0}{\tau }^{\pm }{e}^{\mp }$ is presented. The analysis is performed using a sample of proton-proton collision data, collected with the LHCb detector at a centre-of-mass energy of 13 TeV between 2016 and 2018, corresponding to an integrated luminosity of 5.4 fb${}^{-1}$. No significant signal is observed, and upper limits on the branching fractions are determined to be $\mathcal{B}$$(B^0\to K^{\ast 0}{\tau }^{-}{e}^{+})<5.9$ $(7.1)\times {10}^{-6}$ and $\mathcal{B}$$(B^0\to K^{\ast 0}{\tau }^{+}{e}^{-})<4.9$ $(5.9)\times {10}^{-6}$ at the 90% (95%) confidence level.