  Recently, there appears lots of papers on the possibility of light Dark
Matter (DM) in MeV and sub-GeV scale. Until now, only INTEGRAL and COMPTEL
provided experimental data of 511keV of galactic center, and two spectra of
Galactic Diffuse MeV gammas (GDMG), and COMPTEL provided the Cosmic Background
MeV gammas (CBMG) for wide sky for indirect detection of light DMs. However
except 511keV, those spectra for diffuse gammas included large statistical and
systematic errors in spite of 10 years observation, since both two instruments
suffered from severe background radiation in space. In 2018 April, we
(SMILE-project in Comic-ray Group of Kyoto University) have observed MeV gamma
rays for whole southern sky by Electron Tracking Compton Camera (ETCC) using
JAXA balloon at Australia during one-day. (SMILE2+ Project) By measuring all
parameters of Compton scattering in every gamma, ETCC has achieved for the
first time to obtain the complete direction of MeV gammas as same as optical
telescopes, and also to distinguish signal gammas from huge background gammas
in space clearly. In this observation, ETCC with a large Field of View of 3sr
observed MeV gammas from 3/5 of all sky including galactic centre, a half disk,
crab, and most of CBMG By reconstructing the Compton process, we successfully
obtained pure comic gammas by reducing background by more 2 orders, which is
clearly certificated by the clear enhancement of detected gamma flux with ~30%
during galactic center passing through the Field of View, which is consistent
with the ratio of CBMG and GDMG. Now 511keV gammas GDMG are preliminarily
detected with ~5 and >10 sigma respectively around Galactic Centre. Also we
have obtained near 105events of CBMG in with quite low background of only a few
10% in total CBMG events. Thus we obtained good data for both with high
statistics and very low systematics even one day observation.
