Search for a New B-L Z' Gauge Boson with the NA64 Experiment at CERN

Abstract

A search for a new $Z^{\prime }$ gauge boson associated with (un)broken B-L symmetry in the keV-GeV mass range is carried out for the first time using the missing-energy technique in the NA64 experiment at the CERN SPS. From the analysis of the data with 3.22e11 electrons on target collected during 2016-2021 runs no signal events were found. This allows to derive new constraints on the $Z^{\prime }-e$ coupling strength, which for the mass range $0.3<m_{Z^{\prime }}<100$ MeV are more stringent compared to those obtained from the neutrino-electron scattering data.

6 pages, 3 figures. Revised shorter version, Fig.3 updated, published in Physical Review Letters