Development of Radiative Decay Counter to reduce the background in the MEG experiment

The MEG II experiment is being prepared to search for the μ⁺ → e⁺γ decay with a 10 times higher sensitivity than that of the MEG experiment. In order to improve the sensitivity of the MEG II experiment as much as possible, Radiative Decay Counter (RDC) is being developed as an optional detector. A beam test was done by using a prototype of RDC which consists of two plastic scintillators and four GSO crystals at the end of the beam time for the MEG experiment (in August, 2013). The beam test was finished with success and e-γ coincided events of Radiative Muon Decay (RMD) were observed. In this conference record, details about the beam test are described and results are discussed.