Proof-of-concept study of MeV gamma-ray imaging using a liquid argon time projection chamber for GRAMS

We have developed a small liquid argon time projection chamber (LArTPC) called NanoGRAMS, whose fiducial volume is 5x5x10cm3. A LArTPC has advantages of dense and large volumes sensitive to MeV gamma rays compared with multi-layer semiconductor detectors or gaseous ones. The aim of our work is proof-of-concept studies for one of the important goals of Gamma-Ray and AntiMatter Survey (GRAMS). Our presentation focuses on MeV gamma-ray imaging, by allowing a LArTPC to work as a Compton camera. The NanoGRAMS measures scintillation light and ionized electrons generated by interactions of gamma rays and argon atoms, which are reconstructed to information on the initial energies and momenta of incoming photons. In this talk, we present the design of NanoGRAMS and the results of data analysis.t the design of NanoGRAMS and the results of data analysis.