  Streaming instability is a key mechanism in planet formation, clustering
pebbles into planetesimals. It is triggered at a particular disk location where
the local volume density of solids exceeds that of the gas. After their
formation, planetesimals can grow by feeding from other planetesimals in the
birth ring as well as by accreting inwardly drifting pebbles from the outer
disk.
  To investigate the growth of planetesimals at a single location by the
streaming instability, we test the conditions under which super-Earths are able
to form within the lifetime of the gaseous disk. We modify the \texttt{Mercury}
N-body code to trace the growth and dynamical evolution of a swarm of
planetesimals at the ice line for a solar-mass star. Three distributions of
planetesimal sizes are investigated: (i) a mono-dispersed population of 400 km
radius planetesimals, (ii) a poly-dispersed populations of planetesimals from
200 km up to 1000 km, (iii) a bimodal distribution with a single runaway body
and a swarm of smaller, 100 km size planetesimals.
  The mono-disperse population of 400 km size planetesimals cannot form
$\gtrsim$ Earth mass protoplanets. Their velocity dispersions are quickly
excited, which suppresses both planetesimal and pebble accretion. Planets can
form from the poly-dispersed and bimodal distributions. In these circumstances,
the two-component nature damps the random velocity of the large embryo by small
planetesimals' dynamical friction, allowing the embryo to accrete pebbles
efficiently when it approaches $10^{-2}$ Earth mass. We find that super-Earth
planets are preferred to form when the pebble mass flux is higher, the disk
turbulence is lower, or the Stokes number of the pebbles is higher.
