Search for the violation of time-reversal invariance inKμ30decays

Abstract

The transverse polarization of muons from the decay ${K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}}$ has been recently measured at Brookhaven National Laboratory. A cylindrically symmetric detector was employed with scintillation-counter hodoscopes detecting the charged decay products of the in-flight kaon decay and determining the orientation of the decay plane in the laboratory. Muons were brought to rest in an aluminum polarimeter where they precessed in 60-G magnetic field. The muon polarization was determined from the asymmetric emission of the positron in the muon decay (${\ensuremath{\mu}}^{+}\ensuremath{\rightarrow}{e}^{+}{\ensuremath{\nu}}_{e}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$). With 12\ifmmode\times\else\texttimes\fi{}${10}^{6}$ events collected the mean values measured for the two components of transverse polarization are ${P}_{n}^{\mathrm{lab}}=0.0017\ifmmode\pm\else\textpm\fi{}0.0056$ for the component normal to the decay plane and ${P}_{t}^{\mathrm{lab}}=0.417\ifmmode\pm\else\textpm\fi{}0.063$ for the component in the decay plane. For $\mathrm{Im}\ensuremath{\xi}$, where $\ensuremath{\xi}$ is the ratio of form factors describing ${K}_{\ensuremath{\mu}3}$ decay, we have deduced a value of 0.009\ifmmode\pm\else\textpm\fi{}0.030 which is not significantly different from the value 0.008, expected if time-reversal invariance is valid. We deduce that the average value of the ratio of the normal to transverse components of muon polarization in the kaon rest frame is given by ${〈\frac{{P}_{n}}{{P}_{t}}〉}^{\mathrm{c}.\mathrm{m}.}=0.005\ifmmode\pm\else\textpm\fi{}0.015$.