  Metallic quantum criticality is among the central theme in the understanding
of correlated electronic systems, and converging results between analytical and
numerical approaches are still under calling. In this work, we develop
state-of-art large scale quantum Monte Carlo simulation technique and
systematically investigate the itinerant quantum critical point on a 2D square
lattice with antiferromagnetic spin fluctuations at wavevector
$\mathbf{Q}=(\pi,\pi)$ -- a problem that resembles the Fermi surface setup and
low-energy antiferromagnetic fluctuations in high-Tc cuprates and other
critical metals, which might be relevant to their non-Fermi-liquid behaviors.
System sizes of $60\times 60 \times 320$ ($L \times L \times L_\tau$) are
comfortably accessed, and the quantum critical scaling behaviors are revealed
with unprecedingly high precision. We found that the antiferromagnetic spin
fluctuations introduce effective interactions among fermions and the fermions
in return render the bare bosonic critical point into a new universality,
different from both the bare Ising universality class and the
Hertz-Mills-Moriya RPA prediction. At the quantum critical point, a finite
anomalous dimension $\eta\sim 0.125$ is observed in the bosonic propagator, and
fermions at hot spots evolve into a non-Fermi-liquid. In the
antiferromagnetically ordered metallic phase, fermion pockets are observed as
energy gap opens up at the hot spots. These results bridge the recent
theoretical and numerical developments in metallic quantum criticality and can
be served as the stepping stone towards final understanding of the 2D
correlated fermions interacting with gapless critical excitations.
