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arXiv · 1702.01497

Detecting the $L_μ-L_τ$ gauge boson at Belle II

Takeshi Araki·Shihori Hoshino·Toshihiko Ota·Joe Sato·Takashi Shimomura
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Abstract

We discuss the feasibility of detecting the gauge boson of the $U(1)_{L_μ-L_τ}$ symmetry, which possesses a mass in the range between MeV and GeV, at the Belle-II experiment. The kinetic mixing between the new gauge boson $Z'$ and photon is forbidden at the tree level and is radiatively induced. The leptonic force mediated by such a light boson is motivated by the discrepancy in muon anomalous magnetic moment and also the gap in the energy spectrum of cosmic neutrino. Defining the process $e^{+} e^{-} \rightarrow γZ' \rightarrow γν\barν~(missing~energy)$ to be the signal, we estimate the numbers of the signal and the background events and show the parameter region to which the Belle-II experiment will be sensitive. The signal process in the $L_μ-L_τ$ model is enhanced with a light $Z'$, which is a characteristic feature differing from the dark photon models with a constant kinetic mixing. We find that the Belle-II experiment with the design luminosity will be sensitive to the $Z'$ with the mass $M_{Z'} \lesssim 1 $ GeV and the new gauge coupling $g_{Z'} \gtrsim 8\cdot 10^{-4}$, which covers a half of the unconstrained parameter region that explains the discrepancy in muon anomalous magnetic moment. The possibilities to improve the significance of the detection are also discussed.

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Takeshi Araki, Shihori Hoshino, Toshihiko Ota, Joe Sato, Takashi Shimomura. 2017-03-09. Detecting the $L_μ-L_τ$ gauge boson at Belle II. https://doi.org/10.1103/physrevd.95.055006

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