Published: 2006
Total Pages: 194
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A study of the decay?− → K{sub S}°?−?{sub?} (K{sub S}° →??−) using the BABAR detector is presented. Using 124.4 fb−1 of data we measure?(?− → {bar K}°?−?{sub {tau}}) = (0.830 ± 0.005(stat) ± 0.042(syst))%, which is the world's most precise measurement to date of this branching ratio, and is consistent with the current world average. This preliminary result, unlike most of the?({tau}− → {bar K}°?−?{sub {tau}}) measurements already published, is systematics dominated and so the biggest future improvement to this number should come from reducing the systematic uncertainties in the analysis. A study of the K? mass spectrum, from which the strange (K?) spectral function can be measured, reveals excess contributions above the K*(892) tail at higher K? mass. While in the past this has been thought to be due to K*(892) - K*(1410) interference, we find that the K*(1410), whose branching ratio to K? is approximately 7%, seems insufficient to explain the excess mass observed in the data. Instead, we perform a fit using a K*(892) - K*(1680) interference model and find better agreement. The discrepancy that remains could be due to an s-wave contribution to the interference that is not parameterized in the model used, and/or detector smearing that is not accounted for in our fit. We also attempt to find an s-wave contribution to the K? mass spectrum by searching for an sp-interference effect. While we find a hint that such an effect exists, we have neither the confidence in the statistics nor systematics in the higher K? mass region to announce an observation. We conclude that it would be a worthwhile study to pursue.