  We operated a p-type point contact high purity germanium (PPCGe) detector
(CDEX-1B, 1.008 kg) in the China Jinping Underground Laboratory (CJPL) for
500.3 days to search for neutrinoless double beta ($0\nu\beta\beta$) decay of
$^{76}$Ge. A total of 504.3 kg $\cdot$ day effective exposure data was
accumulated. The anti-coincidence and the multi/single-site event (MSE/SSE)
discrimination methods were used to suppress the background in the energy
region of interest (ROI, $1989-2089$ keV for this work) with a factor of 23. A
background level of 0.33 counts/(keV $\cdot$ kg $\cdot$ yr) was achieved. The
lower limit on the half life of $^{76}$Ge $0\nu\beta\beta$ decay was
constrained as $T_{1/2}^{0\nu}\ > \ {2.2}\times 10^{23}\ \rm yr\ (90\% \
C.L.)$, corresponding to the upper limits on the effective Majorana neutrino
mass: $\langle m_{\beta\beta}\rangle < 2.3-5.2\ \mathrm{eV}$.
