  We present a lattice-QCD calculation of the unpolarized isovector parton
distribution function (PDF) using ensembles at the physical pion mass with
large proton boost momenta $P_z \in \{2.2,2.6,3.0\}$~GeV within the framework
of large-momentum effective theory (LaMET). In contrast to our previous
physical-pion PDF result, we increase the statistics significantly, double the
boost momentum, increase the investment in excited-state contamination
systematics, and switch to $\gamma_t$ operator to avoid mixing with scalar
matrix elements. We use four source-sink separations in our analysis to control
the systematics associated with excited-state contamination. The one-loop LaMET
matching corresponding to the new operator is calculated and applied to our
lattice data. We detail the systematics that affect PDF calculations, providing
guidelines to improve the precision of future lattice PDF calculations. We find
our final parton distribution to be in reasonable agreement with the PDF
provided by the latest phenomenological analysis.
