Measurement of the Branching Ratio and Form Factors for the Decay \boldmath $K_L\to\pi^{\pm}\pi^0e^{\mp}\nu_e(\bar\nu_e)

TL;DR

This paper reports a precise measurement of the decay rate and form factors for the $K_L$ meson decay into pions, electrons, and neutrinos, using CERN data, and confirms previous results with improved accuracy.

Contribution

First precise measurement of the branching ratio and form factors for the $K_L$ decay into $\pi\pi e u$ with higher accuracy than prior studies.

Findings

Branching ratio $Br(K_L o ext{pions} e u)$ measured as $(5.21 imes 10^{-5})$ with small uncertainties.

Form factors $ar{f}_s$, $ar{f}_p$, $ar{ ext{lambda}}_g$, $ar{h}$ agree with previous measurements.

Coupling parameter $L_3$ of the chiral Lagrangian evaluated as $(-4.1 imes 10^{-3})$.

Abstract

The $K_L\to\pi^{\pm}\pi^0e^{\mp}\nu_e(\bar\nu_e)$ decay was investigated with the NA48 detector at CERN SPS using a beam of long-lived neutral kaons. The branching ratio $Br(K_L\to\pi^{\pm}\pi^0e^{\mp}\nu_e(\bar\nu_e))=(5.21\pm 0.07_{stat}\pm 0.09_{syst})\times 10^{-5}$ was fixed from a sample of 5464 events with 62 background events. The form factors $\bar{f}_s$, $\bar{f}_p$, $\lambda_g$ and $\bar{h}$ were found to be in agreement with previous measurements but with higher accuracy. The coupling parameter of the chiral Lagrangian $L_3=(-4.1\pm 0.2)\times 10^{-3}$ was evaluated from the data.