Lepton universality test with K+ --> l+ nu decays

TL;DR

This paper reports a precise measurement of the ratio of decay rates of charged kaons to electrons versus muons, testing lepton universality and confirming Standard Model predictions.

Contribution

It provides a new, precise measurement of the lepton universality ratio $R_K$ using data from the NA62 experiment, supporting the Standard Model.

Findings

Measured $R_K = (2.500 imes 10^{-5})$ with a 0.016 uncertainty

Result is consistent with Standard Model prediction

Supports lepton universality in kaon decays

Abstract

The NA62 experiment at CERN collected a large sample of $K^+\to e^+\nu$ decays during a dedicated run in 2007, which allows a precise test of lepton universality by measurement of the helicity suppressed ratio $R_K = \Gamma(K^+\to e^+\nu)/\Gamma(K^+\to\mu^+\nu)$. The preliminary result of the analysis of a partial data sample of 51089 $K^+\to e^+\nu$ candidates is $R_K=(2.500\pm0.016)\times10^{-5}$, consistent with the Standard Model expectation.