Study of hadronic transitions between Y states and observation of Y(4S)-> eta Y(1S) decay
Abstract
We present a study of hadronic transitions between Y(mS) (m=4,3,2) and Y(nS) (n=2,1) resonances based on 347.5∈vfb of data taken with the BABAR detector at the PEP-II storage rings. We report the first observation of Y(4S)-> eta Y(1S) decay with a branching fraction BR((Y(4S)->eta Y(1S))=(1.96+-0.06stat +-0.09syst) x 10-4 and measure the ratio of partial widths Gamma(Y(4S)->etaY(1S))/Gamma(Y(4S)->pi+pi-Y(1S))=2.41+- 0.40stat+- 0.12syst. We set 90% CL upper limits on the ratios Gamma(Y(2S)->etaY(1S))/Gamma(Y(2S)->pi+pi-Y(1S))<5.2 x10-3$ and Gamma(Y(3S)->etaY(1S))/Gamma(Y(3S)->pi+pi-Y(1S))<1.9x10-2. We also present new measurements of the ratios Gamma(Y(4S)->pi+pi-Y(2S))/Gamma(Y(4S)->pi+pi-Y(1S))=1.16+- 0.16stat+- 0.14syst and Gamma(Y(3S)->pi+pi-Y(2S))/Gamma(Y(3S)->pi+pi-Y(1S))=0.577+- 0.026stat+- 0.060syst.