A search for the rare decays
and
is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13
, corresponding to an integrated luminosity of 2.0
. No significant signal is observed for either decay mode and upper limits on their branching fractions are set using
and
decays as normalization channels. The upper limits are
and
at 95% confidence level for the
and
decay modes, respectively. This is the first reported search for the
decay, while the upper limit on the
branching fraction improves upon the previous best limit.