Cloud-cloud Collision in the Galactic Center 50 km s$^{-1}$ Molecular
  Cloud
  We performed a search of star-forming sites influenced by external factors,
such as SNRs, HII regions, and cloud-cloud collisions, to understand the
star-forming activity in the Galactic center region using the NRO Galactic
Center Survey in SiO $v=0, J=2-1$, H$^{13}$CO$^+ J=1-0$, and CS $J=1-0$
emission lines obtained by the Nobeyama 45-m telescope. We found a half-shell
like feature (HSF) with a high integrated line intensity ratio of $ int T_{
mathrm B}$(SiO $v=0, J=2-1$)$dv$/$ int T_{ mathrm B}$(H$^{13}$CO$^+ J=1-0$)$dv
sim6-8$ in the 50 km s$^{-1}$ molecular cloud, which is a most conspicuous
molecular cloud in the region and harbors an active star-forming site seen as
several compact HII regions. The high ratio in the HSF indicates that the cloud
contains huge shocked molecular gas. The HSF is also seen as a half-shell
feature in the position-velocity diagram. A hypothesis explaining the chemical
and kinetic properties of the HSF is that the feature is originated by a
cloud-cloud collision (CCC). We analyzed the CS $J=1-0$ emission line data
obtained by Nobeyama Millimeter Array to reveal the relation between the HSF
and the molecular cloud cores in the cloud. We made a cumulative core mass
function (CMF) of the molecular cloud cores within the HSF. The CMF in the CCC
region is not truncated at least up to $ sim2500M_ odot$ although the CMF of
the non-CCC region reaches the upper limit of $ sim1500M_ odot$. Most massive
molecular cores with $M_{ mathrm{gas}}>750 M_{ odot}$ are located only around
the ridge of the HSF and adjoin the compact HII region. These may be a sign of
massive star formation induced by CCC in the Galactic center region.
