Muon g-2 and searches for a new leptophobic sub-GeV dark boson in a missing-energy experiment at CERN

TL;DR

This paper proposes a new experimental search at CERN for a sub-GeV dark boson Z_mu, which could explain the muon g-2 anomaly, by detecting missing-energy events in muon scattering experiments with high sensitivity.

Contribution

It introduces a novel missing-energy experimental technique at CERN to search for a leptophobic dark boson Z_mu, with sensitivity surpassing previous bounds and capable of confirming or refuting its role in muon g-2 discrepancy.

Findings

Feasibility of detecting Z_mu via muon scattering with missing energy.

Sensitivity to Z_mu coupling constant exceeds current requirements.

Potential to discover or exclude Z_mu in the near future.

Abstract

The 3.6 \sigma discrepancy between the predicted and measured values of the anomalous magnetic moment of positive muons can be explained by the existence of a new dark boson Z_\mu with a mass in the sub-GeV range, which is coupled predominantly to the second and third lepton generations through the L_\mu - L_\tau current . After a discussion of the present phenomenological bounds on the Z_\mu coupling, we show that if the Z_\mu exists, it could be observed in the reaction \mu+Z \to \mu+Z+Z_\mu of a muon scattering off nuclei by looking for an excess of events with large missing muon beam energy in a detector due to the prompt bremsstrahlung Z_\mu decay Z_\mu \to \nu\nu into a couple of neutrinos. We describe the experimental technique and the preliminary study of the feasibility for the proposed search. We show that this specific signal allows for a the search for the Z_\mu with a sensitivity in the coupling constant \alpha_\mu > 10^{-11}, which is 3 orders of magnitude higher than the value required to explain the discrepancy. We point out that the availability of high-energy and -intensity muon beams at CERN SPS provides a unique opportunity to either discover or rule out the Z_\mu in the proposed search in the near future. The experiment is based on the missing-energy approach developed for the searches for invisible decays of dark photons and (pseudo)scalar mesons at CERN and is complementary to these experiments.