Observation of the Semileptonic D+ Decay into the (K)over-bar(1)(1270)(0) Axial-Vector Meson

Abstract

By analyzing a 2.93 fb(-1) data sample of e(+)e(-) collisions, recorded at a center-of-mass energy of 3.773 GeV with the BESIII detector operated at the BEPCII collider, we report the first observation of the semileptonic D+ transition into the axial-vector meson D+ -> (K) over bar (1) (1270)(0)e(+)nu(e) with a statistical significance greater than 10 sigma. Its decay branching fraction is determined to be B[D+ -> (K) over bar (1) (1270)(0)e(+)nu(e)] = (2.30 +/- 0.26(-0.21)(+0.18) +/- 0.25) x 10(-3), where the first and second uncertainties are statistical and systematic, respectively, and the third originates from the input branching fraction of (K) over bar (1)(1270)(0) -> K-pi(+)pi(0).