OBSERVATION OF chi_b(2P) TO chi_b(1P) pi+ pi-

Abstract

We have searched for the di-pion transition chi_b(2P) to chi_b(1P) pi+ pi- in the CLEO-III sample of Upsilon(3S) decays in the exclusive decay chain, Upsilon(3S) to gamma chi_b(2P), chi_b(2P) to chi_b(1P) pi+ pi-, chi_b(1P) to gamma Upsilon(1S), and, finally, Upsilon(1S) to l+ l-. We refute the null hypothesis, finding a signal greater than 6 sigma deviation from expected background, and thus claim observation of this di-pion decay. For comparisons we have used the well-established channels Upsilon(3S) to Upsilon(2S) pi+ pi-, with either Upsilon(2S) to l+ l- or Upsilon(2S) to gamma chi_b(1P). Under reasonable assumptions, we find the two-pion partial width to be, Gamma_(pi+pi-) = 0.80 +- (0.21) +- (0.23,0.17) keV.