Evidence for the h_b(1P) meson in the decay Upsilon(3S) --> pi0 h_b(1P)

TL;DR

This paper reports evidence for the h_b(1P) meson in Upsilon(3S) decays, observing an excess of events consistent with the meson's mass and measuring the product of relevant branching fractions.

Contribution

First experimental evidence for the h_b(1P) meson in Upsilon(3S) decays, with a measured mass and branching fraction product.

Findings

Observed excess at recoil mass 9902 MeV/c^2

Significance of 3.1 sigma including systematics

Measured product branching fraction (4.3 +/- 1.1(stat) +/- 0.9(syst)) x 10^{-4}

Abstract

Using a sample of 122 million Upsilon(3S) events recorded with the BaBar detector at the PEP-II asymmetric-energy e+e- collider at SLAC, we search for the $h_b(1P)$ spin-singlet partner of the P-wave chi_{bJ}(1P) states in the sequential decay Upsilon(3S) --> pi0 h_b(1P), h_b(1P) --> gamma eta_b(1S). We observe an excess of events above background in the distribution of the recoil mass against the pi0 at mass 9902 +/- 4(stat.) +/- 2(syst.) MeV/c^2. The width of the observed signal is consistent with experimental resolution, and its significance is 3.1sigma, including systematic uncertainties. We obtain the value (4.3 +/- 1.1(stat.) +/- 0.9(syst.)) x 10^{-4} for the product branching fraction BF(Upsilon(3S)-->pi0 h_b) x BF(h_b-->gamma eta_b).