Observation of e+e−→γχc1 and search for e+e−→γχc0 , γχc2 , and γηc at s near 10.6 GeV at Belle
                        
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            In the bottomonium sector, the hindered magnetic dipole transitions between P-wave states , , 1, 2, are expected to be severely suppressed according to the relativized quark model, due to the spin flip of the 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: , and . These values help to constrain the parameters of the coupled-channel models. The results are obtained using a data sample taken around with the Belle detector at the KEKB asymmetric-energy collider. Published by the American Physical Society2025more » « less
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