Abstract

In the bottomonium sector, the hindered magnetic dipole transitions between P-wave states hb(2P)→χbJ(1P)γ, J=0, 1, 2, are expected to be severely suppressed according to the relativized quark model, due to the spin flip of the b quark. Nevertheless, a recent model following the coupled-channel approach predicts the corresponding branching fractions to be enhanced by orders of magnitude. In this Letter, we report the first search for such transitions. We find no significant signals and set upper limits at 90% confidence level on the corresponding branching fractions: B[hb(2P)→γχb0(1P)]<2.7×10−1, B[hb(2P)→γχb1(1P)]<5.4×10−3 and B[hb(2P)→γχb2(1P)]<1.3×10−2. These values help to constrain the parameters of the coupled-channel models. The results are obtained using a 121.4 fb−1 data sample taken around s=10.860 GeV with the Belle detector at the KEKB asymmetric-energy e+e− collider. Published by the American Physical Society 2025