PEN experiment: a precise test of lepton universality

With few open channels and uncomplicated theoretical description, charged pion decays are uniquely sensitive to certain standard model (SM) symmetries, the universality of weak fermion couplings, and to aspects of pion structure and chiral dynamics. We review the current knowledge of the pion electronic decay $\pi^+ \to e^+ \nu_e({\gamma})$, or $\pi_{e2({\gamma})}$, and the resulting limits on non-SM processes. Focusing on the PEN experiment at the Paul Scherrer Institute (PSI), Switzerland, we examine the prospects for further improvement in the near term.
Comment: Talk presented at CIPANP2018. 9 pages, LaTeX, 4 pdf figures, 1 table. arXiv admin note: substantial text overlap with arXiv:1701.05254