A high-precision measurement of the $\pi \rightarrow e \nu$ branching ratio}

The pion decay branching ratio, $ R_{\pi} = \frac{\Gamma\left(\pi \rightarrow e \nu \hspace{1 mm} + \hspace{1 mm} \pi \rightarrow e \nu \gamma \right)}{\Gamma\left(\pi \rightarrow \mu \nu \hspace{1 mm} + \hspace{1 mm} \pi \rightarrow \mu \nu \gamma \right)}$, is an important observable in the Standard Model of particle physics. The value of the $\pi \rightarrow e \nu$ branching ratio has been calculated within the Standard Model to be (1.2352 $\pm$ 0.0002) $\times 10^{-4}$. The PIENU experiment at TRIUMF aims to measure this quantity to a precision of $<$ 0.1\%. This provides a sensitive test of lepton universality, and constraints on many new physics scenarios with mass reach up to 1000 TeV. The measurements are also sensitive to the presence of heavy neutrinos.The current state of the analysis of the PIENU data will be presented.