Sensitivity of the η(') → π0γγ and η' → ηγγ decays to a sub-GeV leptophobic U(1)B boson

The sensitivity of the rare decays eta(') -> pi 0 gamma gamma and eta' -> eta gamma gamma to signatures of a leptophobic B boson in the MeV-GeV mass range is analyzed in this work. By adding an explicit B-boson resonance exchange, eta -> B gamma -> pi 0 gamma gamma, to the Standard Model contributions from vector and scalar meson exchanges, and employing experimental data for the associated branching ratios, it allows us to improve the current constraints on the B-boson mass mB and coupling to Standard Model particles alpha B. From these constraints and the analysis of the available experimental gamma gamma invariant mass distribution, we show that a B-boson signature in the resonant mass range m pi 0 less than or similar to mB less than or similar to m eta is strongly suppressed and would be very difficult to experimentally identify, assuming that the leptophobic B boson only decays to Standard Model particles. In contrast, the limits outside this mass window are less stringent and the corresponding t- and u-channel signatures may still be observable in the data, as it occurs with the nonresonant Standard Model rho, omega and phi meson exchanges. In addition, we make use of experimental data from the eta' -> pi 0 gamma gamma and eta' -> eta gamma gamma decays to explore larger B-boson masses. Our results are relevant for the B-boson search programs at existing and forthcoming light-meson facilities, such as KLOE(-II) and Jefferson Lab Eta Factory experiments.

Automated summary

The sensitivity of rare decays eta(') -> pi 0 gamma gamma and eta' -> eta gamma gamma to a leptophobic B boson is analyzed. By incorporating B-boson resonance exchange and using experimental data, the constraints on B-boson mass and coupling to Standard Model particles are improved. It is found that identifying the B-boson signature in a specific mass range is challenging, but outside that range, the corresponding signatures may still be observable.