First Observation of the P-Wave Spin-Singlet Bottomonium States h(b)(1P) and h(b)(2P)
We report the first observations of the spin-singlet bottomonium states h(b)(1P) and h(b)(2P). The states are produced in the reaction e(+)e(-) --> h(b)(nP)pi(+)pi(-) using a 121.4 fb(-1) data sample collected at energies near the Y(5S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We determine M[h(b)(1P)] = (9898.2(-1.0-1.1)(+1.1+1.0)) MeV/c(2) and M[h(b)(2P)] = (10 259.8 +/- 0.6(-1.0)(+1.4)) MeV/c(2), which correspond to P-wave hyperfine splittings Delta M-HF = (+1.7 +/- 1.5) and (+0.5(-1.2)(+1.6)) MeV/c(2), respectively. The significances of the h(b)(1P) and h(b)(2P) are 5.5 sigma and 11.2 sigma, respectively. We find that the production of the h(b)(1P) and h(b)(2P) is not suppressed relative to the production of the Y(1S), Y(2S), and Y(3S).