Observation of the Semileptonic Decay D0→a0(980)−e+νe and Evidence for D+→a0(980)0e+νe

Using an e+e− collision data sample of 2.93 fb−1 collected at a center-of-mass energy of 3.773 GeV by the BESIII detector at BEPCII, we report the observation of D0→a0(980)−e+νe and evidence for D+→a0(980)0e+νe with significances of 6.4σ and 2.9σ, respectively. The absolute branching fractions are determined to be B(D0→a0(980)−e+νe)×B(a0(980)−→ηπ−)=[1.33−0.29+0.33(stat)±0.09(syst)]×10−4 and B(D+→a0(980)0e+νe)×B(a0(980)0→ηπ0)=[1.66−0.66+0.81(stat)±0.11(syst)]×10−4. This is the first time the a0(980) meson has been measured in a D0 semileptonic decay, which would open one more interesting page in the investigation of the nature of the puzzling a0(980) states.