Abstract
A specially developed scintillator and spark chamber spectrometer has been used to measure recoiling 4He target nuclei, and a magnetic spark chamber spectrometer to measure forward-going pπ +π −particles, selecting coherent events by four-momentum balance. Two enhancements in the pπ +π −mass spectrum are found at 1.49 and 1.71 GeV/ c 2. The branching ratio of the quasi-two-body stateΔ ++π −is42 ± 8%in the 1.71 GeV/ c 2 mass region. The tslope, as a function of pπ +π −mass, is consistent with what can be predicted using the impulse approximation. The decay angular analysis indicates the presence of several interfering states in the 1.5 GeV/c 2mass region and of one state of spin3/2, possibly5/2, in the 1.7 GeV/c 2mass region. There is some preference shown for t-channelhelicity conservation. The data are very similar to results obtained with photon targets, which provides independent support for the hypothesis that vacuum exchange is dominant in the production of low-mass pπ +π −states in pp interactions around 20 GeV/c.
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