  Lorentz and CPT symmetry in the quark sector of the Standard Model are
studied in the context of an effective field theory using ZEUS $e^{\pm} p$
data. Symmetry-violating effects can lead to time-dependent oscillations of
otherwise time-independent observables, including scattering cross sections. An
analysis using five years of inclusive neutral-current deep inelastic
scattering events corresponding to an integrated HERA luminosity of $372\;
\text{pb}^{-1}$ at $\sqrt{s} = 318$ Gev has been performed. No evidence for
oscillations in sidereal time has been observed within statistical and
systematic uncertainties. Constraints, most for the first time, are placed on
42 coefficients parameterising dominant CPT-even dimension-four and CPT-odd
dimension-five spin-independent modifications to the propagation and
interaction of light quarks.
