Blind analysis results of the TWIST experiment

TL;DR

The TWIST experiment conducted a high-precision test of the standard model by analyzing muon decay parameters, achieving an order of magnitude improvement over previous measurements to constrain new physics.

Contribution

This paper presents the final blind analysis results of the TWIST experiment, providing more precise measurements of muon decay parameters and testing the standard model with improved accuracy.

Findings

Achieved an order of magnitude improvement in measurement precision.

Constrained new physics models using decay parameter results.

Validated the standard model predictions within experimental uncertainties.

Abstract

The TRIUMF Weak Interaction Symmetry Test (TWIST) experiment was designed to test the standard model at high precision in the purely leptonic decay of polarized muons. A general four-fermion interaction model is used to describe the muon decay. TWIST measures three of the four muon decay parameters of this model, $\rho$, $\delta$ and $P_{\mu}^{\pi} \xi$, from the shape of the momentum-angle spectrum. The results of this model independent approach are compared to the standard model predictions and used to constrain new physics. Our collaboration has finalized the blind analysis of the final experimental data taken in 2006 and 2007. This analysis mostly reached our goal of a precision of an order of magnitude improvement over the pre-TWIST measurements.