Although it is usually thought that a class of weakly interacting massive particle (WIMP) dark matters (DMs), which have the vector coupling with the $Z$ boson, is denied by null results of the direct DM searches, such WIMP DMs are still viable if they are superheavy with the mass of $m_{DM} gtrsim 10^9$ GeV. In the future, the superheavy WIMP DMs can be searched up to $m_{DM} simeq 10^{12}$ GeV, which corresponds to the so-called neutrino floor limit. We show that the observed abundance of $Omega_mathrm{DM}h^2 simeq 0.1$ for a superheavy WIMP DM can be reproduced by a suitable reheating temperature of $T_R simeq m_{DM}/29$ after inflation, if the direct inflaton decay into DM is negligible or kinematically forbidden.
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