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Report No.

Observation of the radiative decays of $$Upsilon(1S)$$ to $$chi_{c1}$$

Katrenko, P.*; Tanida, Kiyoshi   ; Belle Collaboration*; 168 of others*

We report the first observation of the radiative decay of the $$Upsilon(1S)$$ into a charmonium state. The statistical significance of the observed signal of $$Upsilon(1S) to gamma chi_{c1}$$ is 6.3 standard deviations including systematics. The branching fraction is calculated to be Br($$Upsilon(1S) to gamma chi_{c1}$$) = $$(4.7^{+2.4}_{-1.8} (stat) ^{+0.4}_{-0.5} (sys)) times 10^{-5}$$. We also searched for $$Upsilon(1S)$$ radiative decays into $$chi_{c0,2}$$ and $$eta_c(1S,2S)$$ and set upper limits on their branching fractions. These results are obtained from a 24.9 fb$$^{-1}$$ data sample collected with the Belle detector at the KEKB asymmetric-energy $$e^+e^-$$ collider at a center-of-mass energy equal to the $$Upsilon(2S)$$ mass using $$Upsilon(1S)$$ tagging by the $$Upsilon(2S) to Upsilon(1S) pi^+pi^-$$ transitions.



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Category:Physics, Multidisciplinary



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