First Measurement of the Absolute Branching Fraction of Λ→pμ−¯νμ

• The absolute branching fraction of Lambda -> p mu(-)(upsilon) over bar (mu) is reported for the fast time based on an e(+)e(-) annihilation sample of 10 x 10(9) J/psi events collected with the BESIII detector at N rs = 3.097 GeV. The branching fraction is determined to be B(Lambda -> p mu(-)(upsilon) over bar (mu)). [1.48 +/- 0.21(stat) +/- 0.08(syst)] x 10(-4), which is improved by about 30% in precision over the previous indirect measurements. Combining this result with the world average of B(Lambda -> pe(-)(upsilon) over bar (e)), we obtain the ratio {[Gamma(Lambda -> p mu(-)(upsilon) over bar (mu))]/[Gamma(Lambda -> pe(-)(upsilon) over bar (e))]} to be 0.178 +/- 0.028, which agrees with the standard model prediction assuming lepton flavor universality. The asymmetry of the branching fractions of Lambda -> p mu(-)(upsilon) over bar (mu) and (Lambda) over bar -> (p) over bar mu(+)upsilon(mu) is also determined, and no evidence for CP violation is found.

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

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

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