Evidence for new interference phenomena in the decay D+→K-π+μ+ν

Using a large sample of charm semileptonic decays collected by the FOCUS photoproduction experiment at Fermilab, we present evidence for a small, even spin K(-)pi(+) amplitude that interferes with the dominant (K) over bar *(0) component in the D+ --> K(-)pi(+)mu(+)nu final state. Although this interference significantly distorts the D+ --> K(-)pi(+)mu(+)nu decay angular distributions, the new amplitude creates only a very small distortion to the observed kaon pion mass distribution when integrated over the other kinematic variables describing the decay. Our data can be described by (K) over bar *(0) interference with either a constant amplitude or broad spin zero resonance. (C) 2002 Elsevier Science B.V. All rights reserved.