Аннотация:A search for a new Z0 gauge boson associated with (un)broken B − L symmetry in the keV–GeV massrange is carried out for the first time using the missing-energy technique in the NA64 experiment at theCERN SPS. From the analysis of the data with 3.22 × 1011 electrons on target collected during 2016–2021runs, no signal events were found. This allows us to derive new constraints on the Z0 − e coupling strength,which, for the mass range 0.3 ≲ mZ0 ≲ 100 MeV, are more stringent compared to those obtained from theneutrino-electron scattering data