Abstract: | Using the data sample of an integrated luminosity of 2.93 fb$^{-1}$ taken at
the center-of-mass energy of 3.773 GeV, we search for the Majorana neutrino in
the lepton number violating decays $D o K pi e^+ e^+$. No significant signal
is observed, and the upper limits on the branching fraction at the 90\%
confidence level are set to be $mathcal{B},(D^0 o K^- pi^- e^+
e^+)<2.7 imes10^{-6}$, $mathcal{B},(D^+ o K_S^0 pi^- e^+
e^+)<3.3 imes10^{-6}$ and $mathcal{B},(D^+ o K^- pi^0 e^+
e^+)<8.5 imes10^{-6}$. The Majorana neutrino is searched for with different
mass assumptions ranging from 0.25 to 1.0 GeV/$c^2$ in the decays $D^0 o K^-
e^+
u_N(pi^- e^+)$ and $D^+ o K_S^0 e^+
u_N(pi^- e^+)$, and the upper
limits on the branching fraction at the 90\% confidence level are extracted to
be at the level of $10^{-7} sim 10^{-6}$, depending on the mass of Majorana
neutrino. The constraints on the mixing matrix element $|V_{eN}|^2$ are also
evaluated. |