  Following the first science results of the LUX-ZEPLIN (LZ) experiment, a
dual-phase xenon time projection chamber operating from the Sanford Underground
Research Facility in Lead, South Dakota, USA, we report the initial limits on a
model-independent non-relativistic effective field theory describing the
complete set of possible interactions of a weakly interacting massive particle
(WIMP) with a nucleon. These results utilize the same 5.5 t fiducial mass and
60 live days of exposure collected for the LZ spin-independent and
spin-dependent analyses while extending the upper limit of the energy region of
interest by a factor of 7.5 to 270 keVnr. No significant excess in this high
energy region is observed. Using a profile-likelihood ratio analysis, we report
90% confidence level exclusion limits on the coupling of each individual
non-relativistic WIMP-nucleon operator for both elastic and inelastic
interactions in the isoscalar and isovector bases.
