Τ Branching Fractions
نویسنده
چکیده
The B factories continue to dominate experimental publications on the τ. Since the previous edition of this Review, there have been 15 published papers that have contributed measurements to the τ Listings, including 6 from the BaBar Collaboration and 8 from the Belle Collaboration. Seven of these papers have provided new upper limits on the branching fractions for neutrinoless τ-decay modes. Of the 57 neutrionless τ-decay modes in the τ Listings, 2 are new and 25 have had improved limits set. The upper limits have been reduced by factors that range between 1.1 and 127, and the average reduction factor is 29. There are now 13 measurements and 6 upper limits from Belle and BaBar on branching fractions of conventional τ decay modes, up from 1 measurement and 3 upper limits in the 2006 edition of this Review. For those branching fractions where older non-B-factory measurements existed, the new B-factory measurements have on average about fifty times the number of events as the most precise earlier measurements, and the statistical uncertainties on the B-factory measurements are on average about seven times smaller. However, the systematic uncertainties now greatly exceed the statistical uncertainties on nearly all B-factory branching fraction measurements, except those with the smallest measured branching fractions. For example , the average ratio of systematic to statistical uncertainty of the B-factory measurements of branching fractions larger than 10 −4 is about 6.5, while the average ratio for branching fractions smaller than 10 −4 is about 1.0. Thus, the total uncertainty on the branching fraction measurements from B factories is on average only about 3 times smaller than the previous most precise non-B-factory measurements. The constrained fit to τ branching fractions: The Lepton Summary Table and the List of τ-Decay Modes contain branching fractions for 119 conventional τ-decay modes and upper limits on the branching fractions for 28 other conventional τ-decay modes. Of the 119 modes with branching fractions, 82 are CITATION: C. Amsler et al.
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– 1 – Τ Branching Fractions
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