What can a heavy $U(1)_{\rm B-L}$ $Z^\prime$ boson do to the muon $(g-2)_\mu$ anomaly and to a new Higgs boson mass?

Abstract

The minimal $U(1)_{\rm B-L}$ extension of the Standard Model (B-L-SM) offers an explanation for neutrino mass generation via a seesaw mechanism as well as contains two new physics states such as an extra Higgs boson and a new $Z^\prime$ gauge boson. The emergence of a second Higgs particle as well as a new $Z^\prime$ gauge boson, both linked to the breaking of a local $U(1)_{\rm B-L}$ symmetry, makes the B-L-SM rather constrained by direct searches at the Large Hadron Collider (LHC) experiments. We investigate the phenomenological status of the B-L-SM by confronting the new physics predictions with the LHC and electroweak precision data. Taking into account the current bounds from direct LHC searches, we demonstrate that the prediction for the muon $(g-2)_\mu$ anomaly in the B-L-SM yields at most a contribution of approximately $8.9 \times 10^{-12}$ which represents a tension of $3.28$ standard deviations, with the current $1\sigma$ uncertainty, by means of a $Z^\prime$ boson if its mass lies in a range of $6.3$ to $6.5$ TeV, within the reach of future LHC runs. This means that the B-L-SM, with heavy yet allowed $Z^\prime$ boson mass range, in practice does not resolve the tension between the observed anomaly in the muon $(g-2)_\mu$ and the theoretical prediction in the Standard Model. Such a heavy $Z^\prime$ boson also implies that the minimal value for a new Higgs mass is of the order of 400 GeV.