Evidence for the decay D0→K-π+π-e+νe

Using a 281 pb(-1) data sample collected at the psi(3770) with the CLEO-c detector, we present the first absolute branching fraction measurement of the decay D-0 -> K-pi(+)pi(-)e(+)nu(e) at a statistical significance of about 4.0 standard deviations. We find 10 candidates consistent with the decay D-0 -> K-pi(+)pi(-)e(+)nu(e). The probability that a background fluctuation accounts for this signal is less than 4.1x10(-5). We find B(D-0 -> K-pi(+)pi(-)e(+)nu(e))=[2.8(-1.1)(+1.4)(stat)+/- 0.3(syst)]x10(-4). By restricting the invariant mass of the hadronic system to be consistent with K-1(1270), we obtain the product of branching fractions B(D-0 -> K-1(-)(1270)e(+)nu(e))xB(K-1(-)(1270)-> K-pi(+)pi(-))=[2.5(-1.0)(+1.3)(stat)+/- 0.2(syst)]x10(-4). Using B(K-1(-)(1270)-> K-pi(+)pi(-))=(33 +/- 3)%, we obtain B(D-0 -> K-1(-)(1270)e(+)nu(e))=[7.6(-3.0)(+4.1)(stat)+/- 0.6(syst)+/- 0.7]x10(-4). The last error accounts for the uncertainties in the measured K-1(-)(1270)-> K-pi(+)pi(-) branching fractions.