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Register a new userCharmonium in China: BEPCII/BESIII
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Authors
Frederick A. Harris
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Results based on 106 M $psi$ events and about 226 M $J/psi$ events acquired with the BESIII detector at BEPCII are reported, including a confirmation of the BESII $pbar{p}$ threshold enhancement in $J/psi to gamma pbar{p}$, branching ratios for $chi_{cJ} to pi^0 pi^0$ and $eta eta$, and first measurements of the branching ratios for $psi to pi^0 h_c$ and $h_c to gamma eta_c$, as well as measurements of the mass and width of the $h_c$. Also reported are first observations of the two photon process $psi to gamma gamma J/psi$ and $f_0(980) - a_0(980)$ mixing.
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In recent years, lots of studies of charmonium decays have been performed at BESIII based on large data samples of $J/psi$, $psi(3686)$ and $psi(3770)$. Recent results in searches for radiative transitions of $psi(3770)$ and rare phenomena in charmonium decays, and studies of light hadrons structures and properties will be presented.
Based on $psi(3686)$ decays of 106 million, the 1.31 billion J/psi events and a data sample of $psi(3770)$ with $2.9~fb^{-1}$ integrated luminosity, many analyses are performed. Exclusively baryonic decays of the $psi(3770)$, the radiative transition $psi(3770)togammaeta_c(2S)$, the $psi(3770)$ transition to $chi_{cJ}$, isospin violation decay $chi_{c0,2}topi^0eta_c$, the $C-$parity violation decays $J/psitogammagamma,gammaphi$ are searched for, but no significant signals are observed, and upper limits are set for these decays. The decays of $psi(3770)togammachi_{c1}$ and $J/psitopi^0phi$ signals are observed. These measurements provide more information on the charmonium structure, and the isospin and $C$-parity violation in the charmonium decays.
In 2009, the BESIII experiment has collected about 225M $jpsi$ and 106M $psip$ samples, both of which are the world largest on-peak charmonium production. Based on these dataset, BESIII has made great effort on the study of the charmonium decays, some important of which have been reviewed in this proceeding. In addition, a searching for new physics through the $CP/P$ violation process is reported.
Since few years, a new family of exotic states has been appearing above the open-heavy meson thresholds: the so-called $XYZ$ states. BESIII at the BEPCII $e^+e^-$ collider plays a unique role in the study of those particles in the charmonium sector. Changing the beam energy, BESIII can collect large data samples by means of scans of the resonant region, accessing directly to all vector states. As part of a larger upgrade program, BESIII has planned to increase the center of mass energy to reach $4.7$ GeV: this will allow BESIII to investigate the nature of the $Y(4660)$, that was at first observed by Belle and BaBar after Initial State Radiation only in $pipi psi(2s)$ and $Lambda_c$ $bar{Lambda}_c$ final states. The relative branching ratio seems to point toward a baryonium interpretation of the resonance, as expected in Rossi-Veneziano model. BESIII can directly measure the cross sections around the expected peak position and verify this prediction. In this presentation, the status of the $XYZ$ searches at BESIII will be presented, with a focus also on the plans for the newest data taking and for the $Y(4660)$ studies.
At present very large data samples in the energy region of 2.0-4.6 GeV were accumulated by the BESIII detector, which is operated in the upgraded Beijing electron positron collider (BEPCII). These data samples provide an unprecedented opportunity in the study of light hadron spectra and charmonium(-like) decays. We review some experimental analyses related to isospin violations at BESIII in this proceeding, which can be classify into three categories: isospin violating processes with a $f_0(980)$ or $a^0_0(980)$ production, isospin violating processes with baryon final states, and isospin violating hadronic transitions in the charmonium system.
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