  Tidal disruption events (TDEs) occur when a star orbiting a massive black
hole is sufficiently close to be tidally ripped apart by the black hole. AT
2022cmc is the first relativistic TDE that was observed (and discovered) as an
optically bright and fast transient, showing signatures of non-thermal
radiation induced by a jet which is oriented towards the Earth. In this work,
we present optical linear and circular polarization measurements, observed with
VLT/FORS2 in the $R$-band (which corresponds to the blue/UV part of the
spectrum in rest frame), $\sim$ 7.2 and $\sim$ 12.2 rest-frame days after the
first detection, respectively, when the light curve of the transient had
settled in a bright blue plateau. Both linear and circular polarization are
consistent with zero, $p_{lin}$ = 0.14 $\pm$ 0.73 % and $p_{cir}$ = $-$0.30
$\pm$ 0.53 %. This is the highest S/N linear polarization measurement obtained
for a relativistic TDE and the first circular polarimetry for such a transient.
The non detection of the linear and circular polarization is consistent with
the scenario of AT 2022cmc being a TDE where the thermal component
(disk+outflows) is viewed pole-on, assuming an axially symmetric geometry. The
presence and effect of a jet and/or external shocks are, however, difficult to
disentangle.
