Observation of the ^1P_1 State of Charmonium

Using $(2712.4\pm14.3)\times10^{6}$ $\psi(3686)$ events collected with the BESIII detector at the BEPCII collider, the decay $\eta_c\to\gamma\gamma$ in $J/\psi\to\gamma\eta_c$ is observed for the first time. We determine the product branching fraction $\mathcal{B}(J/\psi\to\gamma\eta_c)\times\mathcal{B}(\eta_c\to\gamma\gamma)=(5.23\pm0.26_{\rm{stat.}}\pm0.30_{\rm{syst.}})\times10^{-6}$. This result is well consistent with the LQCD calculation $(5.34\pm0.16)\times10^{-6}$ from...

While experiment produced a candidate for the 1^P_1 chamonium in the past, it still requires a confirmation. Given the recent progress in the exclusive B decay into charmonia, we now have an opportunity to detect this charmonium (h_c) by measuring the final state of the cascade decay B \to h_c K/K^* \to \gamma \eta_c K/K^*. Confirmation of h_c may turn out to be much easier in the B decay than at charm factories though one will have to work a little harder for a high precisio...

This review briefly outlines recent experimental results from the charmonium system. These include new measurements of the M1 radiative transition rates $B(\psi(1S,2S)\to\gamma\eta_c(1S))$; new insights into the mass of the $\eta_c(1S)$; the observation of $J/\psi(1S)$ decays to three photons; new measurements of the two-photon widths of the $\chi_{cJ}(1P)$; the observation of radiative decays of the $\chi_{cj}(1P)$ to light quarks; a precise measurement of the $h_c(1P)$ mass...

Recent experimental results on charmonium $h_c(^1P_1)$, $\eta_c(1S)$ and $\eta_c(2S)$ from Belle, BaBar, CLEO and BESIII are reviewed. $h_c$ production and properties, the $\eta_c(1S)$ lineshape and the observation of $\eta_c(2S)$ in $\psi'$ decays are discussed.

In this talk, we will present the results on the charmonium spin singlet states below the open charm threshold, including h_c, \eta_c, and \eta_c(2S). The masses, widthes, and production rates of these states will be reported. The results are based on a data sample of 106 million \psi' events collected with the BESIII experiments at the BEPCII collider.

The mass splitting between the quarkonium spin-singlet state $h$ ($J^{PC} = 1^{+-}$) and the spin average of the quarkonium spin-triplet states $\chi$ ($J^{PC} = 0^{++}, 1^{++}, 2^{++}$) is seen to be astonishingly small, not only in the charmonium and bottomonium cases where the relevant masses have been measured, but in positronium as well. We find, both in nonrelativistic quark models and in NRQCD, that this hyperfine splitting is so small that it can be used as a test of ...

In this talk, I review the recent experimental developments on charmonium. These mainly include the precision measurements of spin-singlet states $\etac$, $\etac(2S)$, $h_c$, studies of the charmonium-like states X(3872) and the $Y$ states. Charmonium transitions and decays are also discussed.

Hadronic decays of the P-wave spin-triplet charmonium states \chi_cJ (J=0,1,2) are studied using a sample of \psi(2S) decays collected by the BES detector operating at the BEPC storage ring. Branching fractions for the decays \chi_c1 going to K_s^0 K^+ \pi^- + c.c., \chi_c0 going to K_s^0 K_s^0, \chi_c2 going to K_s^0 K_s^0, \chi_c0 going to \phi \phi, \chi_c2 going to \phi \phi and \chi_cJ going to K^+ K^- K^+ K^- are measured for the first time, and those for \chi_cJ going ...

Using a sample of 106 million \psi(3686) events collected with the BESIII detector at the BEPCII storage ring, we have made the first measurement of the M1 transition between the radially excited charmonium S-wave spin-triplet and the radially excited S-wave spin-singlet states: \psi(3686)\to\gamma\eta_c(2S). Analyses of the processes \psi(2S)\to \gamma\eta_c(2S) with \eta_c(2S)\to \K_S^0 K\pi and K^+K^-\pi^0 gave an \eta_c(2S) signal with a statistical significance of greate...

In recent years the B-factories and other machines have found evidence for a large number of new states with hidden charm: candidate h_c(1P), eta_c(2S), and chi_{c2}(2P) states; the well-established X(3872); enhancements called X(3940), Y(3940), and Y(4260); and a new structure at 4350 MeV. Various conventional-charmonium and more exotic interpretations of these data have been proposed. In this talk we review the current state of the experimental evidence and the prospects fo...