Observation of the Leptonic Decay D+ -> T+ Yr

• We report the first observation of D+ -> tau(+) nu(tau), with a significance of 5.1 sigma. We measure beta(D+ tau+nu(tau)) = (1.20 0.12S)t) x 10-3. Taking the world average B(D- /./ v) = (3.74 0.17) x 10-4, we obtain R=ire=1-4(0 rlyr)/F(T) y p = 3.21 0.64,tat 0.43,9,,., which is consistent with the standard model expectation of lepton flavor universality. Using external inputs, our results give values for the Tr decay constant fn. and the Cabibbo-Kobayashi-Maskawa matrix element V,r that are consistent with, but less precise than, other determinations.

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NATURVETENSKAP  -- Fysik -- Subatomär fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Subatomic Physics (hsv//eng)

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