Secluded U(1) below the weak scale

TL;DR

This paper explores a weakly coupled U(1) extension of the Standard Model below 1 GeV, analyzing its implications for muon g-2, rare decays, and the HyperCP anomaly, proposing experimental tests to confirm or refute the model.

Contribution

It identifies a specific parameter space for a secluded U(1) gauge boson that can explain the HyperCP anomaly and affect muon g-2, providing new constraints and experimental strategies.

Findings

A U(1) gauge boson with mass 214 MeV and mixing angle > 3×10^{-5} is consistent with HyperCP data.

The model predicts a few parts in 10^{-9} correction to muon g-2, potentially resolving existing discrepancies.

Proposes high-resolution e^+e^- and kaon decay experiments to test the model.

Abstract

A secluded U(1) sector with weak admixture to photons, O(10^{-2}-10^{-3}), and the scale of the breaking below 1 GeV represents a natural yet poorly constrained extension of the Standard Model. We analyze g-2 of muons and electrons together with other precision QED data, as well as radiative decays of strange particles to constrain mass--mixing angle (m_V-\kappa) parameter space. We point out that m_V = 214 MeV and \kappa^2 > 3\times 10^{-5} can be consistent with the hypothesis of HyperCP collaboration, that seeks to explain the anomalous energy distribution of muon pairs in the \Sigma^+ \to p \mu^+\mu^- process by a resonance, without direct contradiction to the existing data on radiative kaon decays. The same parameters lead to O({\rm few} \times 10^{-9}) upward correction to the anomalous magnetic moment of the muon, possibly relaxing some tension between experimental value and theoretical determinations of g-2. The ultra-fine energy resolution scan of e^+e^-\to \mu^+\mu^- cross section and dedicated analysis of lepton spectra from K^+\to \pi^+ e^+e^- decays should be able to provide a conclusive test of this hypothesis and improve the constraints on the model.