First search for sidereal and annual modulation of $Z$-pole asymmetries with the recovered SLD data set

Abstract

We report what is, to our knowledge, the first time-resolved analysis of electroweak asymmetries at the $Z$ pole, using the public release of the recovered SLD collision data: $6.6\times10^5$ polarized $e^+e^-\to Z$ events from the 1996-1998 SLC runs, with 385583 selected hadronic $Z$ decays spanning 782 sidereal cycles. The left-right asymmetry $A_{LR}$, reconstructed with the published SLD selection and per-event signed Compton polarization, shows no sidereal, solar-diurnal, or annual modulation; a simultaneous unbinned likelihood fit bounds the sidereal first-harmonic amplitude at 0.0086 (95% C.L., statistical). The analysis, frozen on the initial partial release, applied unchanged to the 229833 events of the later-released 1998 run confirms the null (amplitude 0.0018, p=0.90). Using the as-built SLC beam azimuth from the release's documentation corpus, we bound the asymmetry's anisotropy tensor in the Sun-centered frame: $ρ_1\le0.060$, $ρ_2\le0.18$, and, for vector backgrounds, $ρ_0\le0.092$ (95% C.L.). A leading-order matching maps these onto minimal Standard-Model-Extension coefficients as $10^{-2}$-level sensitivities to the two-time-index block of the electroweak gauge-sector coefficient $k_W$ (components with no existing laboratory constraint) and to the Higgs-sector coefficient $k_{ϕϕ}$; the insertions split the $Z$ pole by polarization, so for the tensor families assessed the resonance saturates the sidereal amplitude near $10^{-2}$ and the Born-model bounds exclude finite coefficient bands rather than set an upper limit. We also derive a previously unpublished $Z$-pole birefringence channel in the helicity-odd azimuthal modulation of the thrust axis, with response enhanced by about $2M_Z/Γ_Z$; a Born-level pilot is null. First sidereal analyses of hadronization and leptonic asymmetries bound instrumental drifts at the $10^{-4}$-$10^{-3}$ fractional level.