First Observation of A? plus and A?- Signals near the ?KN(I=1) Mass Threshold in Ac plus ? A? plus ? plus ?- Decay
Abstrakt
Using the data sample of 980 fb-1 collected with the Belle detector operating at the KEKB asymmetric -energy e+e- collider, we present the results of an investigation of the Az+ and Az- invariant mass distributions looking for substructure in the decay A+c -> Az+z+z-. We find a significant signal in each mass distribution.
When interpreted as resonances, we find for the Az+ (Az-) combination a mass of 1434.3 +/- 0.6(stat) +/- 0.9(syst) MeV=c2 [1438.5 +/- 0.9(stat) +/- 2.5(syst) MeV=c2], an intrinsic width of 11.5 +/- 2.8(stat) +/- 5.3(syst) MeV=c2 [33.0 +/- 7.5(stat) +/- 23.6(syst) MeV=c2] with a significance of 7.5u (6.2u). As these two signals are very close to the over bar KN threshold, we also investigate the possibility of a over bar KN cusp, and find that we cannot discriminate between these two interpretations due to the limited size of the data sample.