New, high statistics measurement of the K+ -> pi0 e+ neutrino (K+e3) branching ratio

TL;DR

This paper reports a high-statistics measurement of the K+ -> pi0 e+ neutrino branching ratio, finding a value slightly higher than previous estimates, with implications for CKM matrix unitarity.

Contribution

The study provides a new, precise measurement of the K+e3 branching ratio using a novel detection method that does not require photon detection.

Findings

Measured BR(K+e3gamma) = (5.13 +- 0.02stat +- 0.09sys +- 0.04norm)%

Result is ~2.3 sigma higher than PDG value

Discusses implications for Vus and CKM unitarity

Abstract

E865 at the Brookhaven National Laboratory AGS collected about 70,000 K+e3 events with the purpose of measuring the K+e3 branching ratio relative to the observed K+ ->pi+pi0, K+ -> pi0 mu+ neutrino, and K+ -> pi+ pi0 pi0 decays. The pi0 in all the decays was detected using the e+e- pair from pi0 -> e+e- gamma decay and no photons were required. Using the Particle Data Group branching ratios for the normalization decays we obtain BR(Ke3gamma) = (5.13 +- 0.02stat +- 0.09sys +- 0.04norm)%, where K+e3gamma includes the effect of virtual and real photons (inclusive measurement). This result is ~ 2.3 sigma higher than the current Particle Data Group value. The implications of this result for the Vus element of the CKM matrix, and the matrix's unitarity are discussed.