MEASUREMENT OF p-w INTERFERENCE IN THE REACTION n-p -+ 7r+7r-n at 15 GeV/c*

In a study of the reaction 7r-p -+n+n-n at 15 GeV/c we observe pronounced p-o interference effects between the transverse helicity states of the vector mesons. The relative phase of the interfering amplitudes is determined to be -1.4OiO. 45 rad, and the branching ratio 0 -*2n is found to be 2.1 +2.8 -o . g %. (Submitted to Phys. Rev. Letters) *Work supported by the U. S. Atomic Energy Commission. ** Present address, Rutherford High Energy Laboratory, Chilton, Didcot, Berkshire, England. t Present address, Institut fiir Hochenergiephysik, Heidelberg, Germany. tt Present address, Brookhaven National Laboratory. In 1961, Glashow’ suggested that spectacular I-spin violating electromagnetic interference effects between the p and w meson might be observed in the dipion mass spectrum since the masses of the two particles were so nearly identical. Many searches for the p-o interference effect have been made, 2 and recently, the existence of p-w mixing has been conclusively demonstrated in several high statistics experiments. 2-7 There remains, however, substantial uncertainty about the precise nature of the mixing parameters, particularly for the strong production experiments. Moreover, the effect has been observed only at low energies so that high energy behavior is unknown. We present here the results of a wire spark-chamber experiment, performed at the Stanford Linear Accelerator Center, which studies po interference in the reaction ?r-p --+r+r-n at an incident beam momentum of 15 GeV/c. We find a strong p -o interference in the transverse polarization states of the mesons with an overall relative phase of = 7J2 (rad). Detailed descriptions of our apparatus and genera1 methods of analysis have been published previously. 8 The properties of the apparatus of particular importance for this experiment are as follows: The acceptance of the spectrometer varied slowly as a function of the dipion mass (rnrr) and the momentum transfer squared to the nucleon (t). The acceptance was zero for very asymmetric decays ( ]cosBHI > 0.8 where 8 H is the polar angle of the outgoing 7rin the helicity frame) and was peaked near cos0 H =0 with the result that the observed data distributions preferentially contained transverse p and o decays. The mass resolution of the spectrometer at the o mass was calculated from the measurement uncertainties in the spark chambers to be -It8 MeV. This resolution was verified by observation of the decay KS0 + 7rfnwhich also implied a resolution of 8 MeV in the region of the U. The absolute mass scale calibration was