Katrenko, P.Adachi, IAihara, H.Al Said, S.Asner, D. M.Aushev, T.Badhrees, IBahinipati, S.Behera, P.Beleno, C.Bennett, J.Bhardwaj, VBhuyan, B.Biswal, J.Bobrov, A.Bonvicini, G.Bracko, M.Campajola, M.Cao, L.Cervenkov, D.Chekelian, VChen, A.Cheon, B. G.Chilikin, K.Cho, H. E.Cho, K.Choi, S. K.Choi, Y.Choudhury, S.Cinabro, D.Cunliffe, S.Di Capua, F.Di Carlo, S.Dolezal, Z.Dong, T. V.Eidelman, S.Epifanov, D.Fast, J. E.Fulsom, B. G.Garg, R.Gaur, VGabyshev, N.Garmash, A.Giri, A.Goldenzweig, P.Golob, B.Grzymkowska, O.Hartbrich, O.Hayasaka, K.Hayashii, H.Hou, W. S.Iijima, T.Inami, K.Ishikawa, A.Itoh, R.Iwasaki, M.Iwasaki, Y.Jacobs, W. W.Jeon, H. B.Jia, S.Jin, Y.Joffe, D.Joo, K. K.Karyan, G.Kichimi, H.Kim, D. Y.Kim, K. T.Kim, S. H.Kinoshita, K.Kodys, P.Korpar, S.Krizan, P.Kroeger, R.Kuhr, T.Lee, I. S.Lee, S. C.Lewis, P.Li, Y. B.Li Gioi, L.Libby, J.Lieret, K.MacQueen, C.Masuda, M.Matsuda, T.Matvienko, D.Merola, M.Miyabayashi, K.Miyata, H.Mizuk, R.Mohanty, G. B.Moon, T. J.Mori, T.Mussa, R.Nakano, E.Nakano, T.Nakao, M.Nayak, M.Nisar, N. K.Nishida, S.Nishimura, K.Ono, H.Onuki, Y.Oskin, P.Pakhlov, P.Pakhlova, G.Pang, T.Pardi, S.Park, C. W.Park, H.Park, S. H.Paul, S.Pedlar, T. K.Pestotnik, R.Piilonen, L. E.Popov, VPrencipe, E.Prim, M. T.Ritter, M.Rostomyan, A.Rout, N.Russo, G.Sahoo, D.Sakai, Y.Sandilya, S.Sanuki, T.Savinov, VSchneider, O.Schnell, G.Schueler, J.Schwanda, C.Seino, Y.Senyo, K.Sevior, M. E.Shen, C. P.Shiu, J. G.Solovieva, E.Staric, M.Stottler, Z. S.Sumiyoshi, T.Sutcliffe, W.Takizawa, M.Tamponi, U.Tanida, K.Tenchini, F.Trabelsi, K.Uchida, M.Uehara, S.Uglov, T.Unno, Y.Uno, S.Urquijo, P.Usov, Y.Van Tonder, R.Varner, G.Vossen, A.Wang, B.Wang, C. H.Wang, M. Z.Wang, P.Wang, X. L.Won, E.Yang, S. B.Ye, H.Yelton, J.Yin, J. H.Yuan, C. Z.Yusa, Y.Zhang, Z. P.Zhilich, VZhukova, V2020-04-122020-04-122020-04-122020-03-2610.1103/PhysRevLett.124.122001https://infoscience.epfl.ch/handle/20.500.14299/168149WOS:000522195100004We report the first observation of the radiative decay of the Upsilon(1S) into a charmonium state. The significance of the observed signal of Upsilon(1S) -> gamma chi(c1) is 6.3 standard deviations including systematics. The branching fraction is calculated to be B[Upsilon(1S) -> gamma chi(c1)] = [4.7(-1.8)(+2.4) (stat)(-0.5)(+0.4) (sys) x 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) -> Upsilon(1S)pi(+)pi(-) transitions.Physics, MultidisciplinaryPhysicstext::journal::journal article::research article