Result of the MICROSCOPE Weak Equivalence Principle test

TL;DR

The MICROSCOPE space mission tested the Weak Equivalence Principle with unprecedented precision, finding no violation down to 2.7×10⁻¹⁵, significantly improving previous limits and confirming the principle's validity.

Contribution

This paper reports the first high-precision space-based test of the Weak Equivalence Principle using two different test masses, achieving an order of magnitude improvement over previous ground-based experiments.

Findings

No violation of the Equivalence Principle detected within the measurement limits.

The Eötvös parameter measured as [-1.5 ± 2.3 (stat) ± 1.5 (syst)] × 10⁻¹⁵.

Improves the previous best test by nearly two orders of magnitude.

Abstract

The space mission MICROSCOPE dedicated to the test of the Equivalence Principle (EP) operated from April 25, 2016 until the deactivation of the satellite on October 16, 2018. In this analysis we compare the free-fall accelerations ($a_{\rm A}$ and $a_{\rm B}$) of two test masses in terms of the E\"otv\"os parameter $\eta({\rm{A, B}}) = 2 \frac{a_{\rm A}- a_{\rm B}}{a_{\rm A}+ a_{\rm B}}$. No EP violation has been detected for two test masses, made from platinum and titanium alloys, in a sequence of 19 segments lasting from 13 to 198 hours down to the limit of the statistical error which is smaller than $10^{-14}$ for $ \eta({\rm{Ti, Pt}})$. Accumulating data from all segments leads to $\eta({\rm{Ti, Pt}}) =[-1.5\pm{}2.3{\rm (stat)}\pm{}1.5{\rm (syst)}] \times{}10^{-15}$ showing no EP violation at the level of $2.7\times{}10^{-15}$ if we combine stochastic and systematic errors quadratically. This represents an improvement of almost two orders of magnitude with respect to the previous best such test performed by the E\"ot-Wash group. The reliability of this limit has been verified by comparing the free falls of two test masses of the same composition (platinum) leading to a null E\"otv\"os parameter with a statistical uncertainty of $1.1\times{}10^{-15}$.