MICROSCOPE mission: final results of the test of the Equivalence Principle

TL;DR

The MICROSCOPE mission tested the Weak Equivalence Principle with unprecedented precision, finding no violation and setting strong constraints on potential differences between inertial and gravitational masses.

Contribution

This study provides the first high-precision experimental test of the WEP in space using differential accelerometers over a two-and-a-half-year mission.

Findings

No violation of the WEP detected within the measurement sensitivity.

E"otv"os parameter constrained to approximately 2.3×10^{-15}.

Systematic uncertainties characterized and corrected for thermal and transient effects.

Abstract

The MICROSCOPE mission was designed to test the Weak Equivalence Principle (WEP), stating the equality between the inertial and the gravitational masses, with a precision of $10^{-15}$ in terms of the E\"otv\"os ratio $\eta$. Its experimental test consisted of comparing the accelerations undergone by two collocated test masses of different compositions as they orbited the Earth, by measuring the electrostatic forces required to keep them in equilibrium. This was done with ultra-sensitive differential electrostatic accelerometers onboard a drag-free satellite. The mission lasted two and a half years, cumulating five-months-worth of science free-fall data, two thirds with a pair of test masses of different compositions -- Titanium and Platinum alloys -- and the last third with a reference pair of test masses of the same composition -- Platinum. We summarize the data analysis, with an emphasis on the characterization of the systematic uncertainties due to thermal instabilities and on the correction of short-lived events which could mimic a WEP violation signal. We found no violation of the WEP, with the E\"otv\"os parameter of the Titanium and Platinum pair constrained to $\eta({\rm Ti, Pt})~=~ [-1.5 \pm 2.3~{\rm (stat)} \pm 1.5~{\rm (syst)}]~\times 10^{-15}$ at $1\sigma$ in statistical errors.