  We present constraints on weakly interacting massive particles (WIMP)-nucleus
scattering from the 2013 data of the Large Underground Xenon dark matter
experiment, including $1.4\times10^{4}\;\mathrm{kg\; day}$ of search exposure.
This new analysis incorporates several advances: single-photon calibration at
the scintillation wavelength, improved event-reconstruction algorithms, a
revised background model including events originating on the detector walls in
an enlarged fiducial volume, and new calibrations from decays of an injected
tritium $\beta$ source and from kinematically constrained nuclear recoils down
to 1.1 keV. Sensitivity, especially to low-mass WIMPs, is enhanced compared to
our previous results which modeled the signal only above a 3 keV minimum
energy. Under standard dark matter halo assumptions and in the mass range above
4 $\mathrm{GeV}\,c^{-2}$, these new results give the most stringent direct
limits on the spin-independent WIMP-nucleon cross section. The 90% C.L. upper
limit has a minimum of 0.6 zb at 33 $\mathrm{GeV}\,c^{-2}$ WIMP mass.
