Measurement Of The K+Mu-3 Decay Spectrum And Form-Factors

The Dalitz-plot density of a sample of 3973 K/sup +//sub mu3/ decays in flight at 1.8 GeV/c (K/sup +/ ..-->.. ..pi../sup 0/..mu../sup +/..nu../sub ..mu../) was studied to determine lambda/sub +/ and lambda/sub 0/, the linear coefficients of the t dependence of the vector and scalar form factors, where t is the four-momentum transfer to the lepton pair. The ..mu../sup +/ was detected by scintillator hodoscopes, identified by thick-plate optical spark chambers and momentum analyzed in a magnetic spectrometer. The ..pi../sup 0/ was detected by its decay into two ..gamma..'s which converted in a lead--optical-spark-chamber--scintillator sandwich detector. The measured coefficients were lambda/sub +/=0.050 +- 0.013 and lambda/sub 0/=0.029 +- 0.011. The chi/sup 2/ of the fit was 63 for 57 degrees of freedom.