Search for hadronic transition $chi_{cJ}toeta_{c}pi^{+}pi^{-}$ and observation of $chi_{cJ}to Kbar{K}pipipi$

Hadronic transitions of $chi_{cJ}to eta_{c}pi^{+}pi^{-}$ (J=0, 1, 2) are searched for using a sample of $1.06times 10^{8}$ $psi(3686)$ events collected with the BESIII detector at the BEPCII storage ring. The $etac$ is reconstructed with $K_{S}^{0}K^{+}pi^{-}+c.c.$ and $K^{+}K^{-}pi^{0}$ final states. No signals are observed in any of the three $chi_{cJ}$ states in either $etac$ decay mode. At the 90% confidence level, the upper limits are determined to be $BR(chi_{c0}to eta_{c}pi^{+}pi^{-})<0.07%$, $BR(chi_{c1}to eta_{c}pi^{+}pi^{-})<0.32%$, and $BR(chi_{c2}to eta_{c}pi^{+}pi^{-})<0.54%$. The upper limit of $BR(chi_{c1}to eta_{c}pi^{+}pi^{-}$ is lower than the existing theoretical prediction by almost an order of magnitude. The branching fractions of $chi_{cJ}to K_{S}^{0}K^{+}pi^{-}pi^{+}pi^{-}+c.c.$, $K^{+}K^{-}pi^{+}pi^{-}pi^{0}$, $omega K^{+}K^{-}$ and $phipi^{+}pi^{-}pi^{0}$ (J=0, 1, 2) are measured for the first time.

Experimental study of psi decays to K+K- pi^0 and K+K- eta

Using $(106pm4)times 10^6$ $psip$ events accumulated with the BESIII detector at the BEPCII $e^+e^-$ collider, we present measurements of the branching fractions for psi decays to $K^{+}K^{-}pi^{0}$ and $K^{+}K^{-}eta$. In these final states, the decay $psito K_2^{*}(1430)^+K^-+c.c.$ is observed for the first time, and its branching fraction is measured to be $(7.12pm{0.62}{rm (stat.)}^{+1.13}_{-0.61}{rm (syst.)})times 10^{-5}$, which indicates a violation of the helicity selection rule in $psip$ decays. The branching fractions of $psito K^*(892)^+K^-+c.c., phieta, phipi^0$ are also measured. The measurements are used to test the QCD predictions on charmonium decays.

Observation of $e^{+}e^{-} to eta J/psi$ at center-of-mass energy $sqrt{s}=4.009$ GeV

Using a 478 pb$^{-1}$ data sample collected with the BESIII detector operating at the BEPCII storage ring at a center-of-mass energy of $sqrt{s}=4.009$ GeV, the production of $e^{+}e^{-}to eta Jpsi$ is observed for the first time with a statistical significance of greater than $10sigma$. The Born cross section is measured to be $(32.1pm 2.8 pm 1.3)$ pb, where the first error is statistical and the second systematic. Assuming the $eta Jpsi$ signal is from a hadronic transition of the $psi(4040)$, the fractional transition rate is determined to be ${cal B}(psi(4040)to eta Jpsi)=(5.2pm 0.5pm 0.2pm 0.5)times 10^{-3}$, where the first, second, and third errors are statistical, systematic, and the uncertainty from the $psi(4040)$ resonant parameters, respectively. The production of $e^{+}e^{-} to pi^0 Jpsi$ is searched for, but no significant signal is observed, and ${cal B}(psi(4040)to pi^0 Jpsi) < 2.8 times 10^{-4}$ is obtained at the 90% confidence level.

Evidence for $eta_{c} rightarrow gammagamma$ and Measurement of $J/psirightarrow 3gamma$

The decay of $J/psi$ to three photons is studied using $psi(3686)topi^+pi^-J/psi$ in a sample of $1.0641times10^8$ $psi(3686)$ events collected with the BESIII detector. Evidence of the direct decay of $eta_c$ to two photons, $eta_ctogammagamma$, is reported, and the product branching fraction is determined to be $mathcal{B}(J/psitogammaeta_c,eta_cto gammagamma)=(4.5pm1.2pm0.6)times10^{-6}$, where the first error is statistical and the second is systematic. The branching fraction for $J/psito3gamma$ is measured to be $(11.3pm1.8pm2.0)times 10^{-6}$ with improved precision.

Observation of chi_{cJ} Decays to Lambda Lambda barpi^{+}pi^{-}

Decays of the chi_{cJ} states (J=0, 1, 2) to Lambda Lambda bar pi^{+} pi^{-}, including processes with intermediate Sigma(1385), are studied through the E1 transition psi-->gamma chi_{cJ} using 106 million psi events collected with the BESIII detector at BEPCII. This is the first observation of chi_{cJ} decays to the final state LambdaLambda bar pi^{+}pi^{-}. The branching ratio of the intermediate process chi_{cJ}-->Sigma(1385)^{+/-} bar{Sigma}(1385)^{-/+} is also measured for the first time, and the results agree with the theoretical predictions based on the color-octet effect.

First observation of the isospin violating decay $J/psirightarrow Lambdabar{Sigma}^{0}+c.c.$

Using a sample of $(225.2pm 2.8)times 10^6$ $J/psi$ events collected with the BESIII detector, we present results of a study of $J/psirightarrow gammaLambdabar{Lambda}$ and report the first observation of the isospin violating decay $J/psirightarrowLambdabar{Sigma}^{0}+c.c.$, in which $bar{Sigma}^{0}$ decays to $gamma bar{Lambda}$. The measured branching fractions are $mathcal{B}(J/psirightarrowbar{Lambda}Sigma^{0}$) = $(1.46pm0.11pm0.12) times10^{-5}$ and $mathcal{B}(J/psirightarrowLambdabar{Sigma^{0}}$) = $(1.37pm0.12pm0.11) times10^{-5}$. We search for $Lambda(1520) rightarrow gamma Lambda$ decay, and find no evident signal, and an upper limit for the product branching fraction $mathcal{B}(J/psirightarrowLambdabar{Lambda}(1520)+c.c.)times mathcal{B}(Lambda(1520)rightarrowgammaLambda)<4.1 times10^{-6}$ is set at the 90% confidence level. We also report the observation of $eta_{c}rightarrowLambdabar{Lambda}$ in $J/psi rightarrow gamma eta_{c}$, $eta_{c}rightarrowLambdabar{Lambda}$ and measure the branching fraction $mathcal{B}(eta_{c}rightarrowLambdabar{Lambda}) =(1.16pm0.12 (stat)pm0.19(syst)pm0.28(PDG))times10^{-3}$.

First observation of the M1 transition $psi(3686)to gammaeta_c(2S)$

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)togammaeta_c(2S). Analyses of the processes psi(2S)to gammaeta_c(2S) with eta_c(2S)to K_S^0 Kpi and K^+K^-pi^0 gave an eta_c(2S) signal with a statistical significance of greater than 10 standard deviations under a wide range of assumptions about the signal and background properties. The data are used to obtain measurements of the eta_c(2S) mass (M(eta_c(2S))=3637.6pm 2.9_mathrm{stat}pm 1.6_mathrm{sys} MeV/c^2), width (Gamma(eta_c(2S))=16.9pm 6.4_mathrm{stat}pm 4.8_mathrm{sys} MeV), and the product branching fraction (BR(psi(3686)to gammaeta_c(2S))times BR(eta_c(2S)to Kbar Kpi) = (1.30pm 0.20_mathrm{stat}pm 0.30_mathrm{sys})times 10^{-5}). Combining our result with a BaBar measurement of BR(eta_c(2S)to Kbar K pi), we find the branching fraction of the M1 transition to be BR(psi(3686)togammaeta_c(2S)) = (6.8pm 1.1_mathrm{stat}pm 4.5_mathrm{sys})times 10^{-4}.

Evidence for the Direct Two-Photon Transition from $psi(3686)$ to $J/psi$

The two-photon transition $psi(3686)togammagamma J/psi$ is studied in a sample of 106 million $psi(3686)$ decays collected by the BESIII detector. The branching fraction is measured to be $(3.1pm0.6(unit{stat})^{+0.8}_{-1.0}(unit{syst})) times10^{-4}$ using $J/psito e^+e^-$ and $J/psitomu^+mu^-$ decays, and its upper limit is estimated to be $4.5times10^{-4}$ at the 90% conference level. This work represents the first measurement of a two-photon transition among charmonium states. The orientation of the $psi(3686)$ decay plane and the $J/psi$ polarization in this decay are also studied. In addition, the product branching fractions of sequential $E1$ transitions $psi(3686)togammachi_{cJ}, chi_{cJ}togamma J/psi (J=0,1,2)$ are reported.

Precision measurement of the branching fractions of J/psi -> pi+pi-pi0 and psi -> pi+pi-pi0

We study the decays of the J/psi and psi mesons to pi+pi-pi0 using data samples at both resonances collected with the BES III detector in 2009. We measure the corresponding branching fractions with unprecedented precision and provide mass spectra and Dalitz plots. The branching fraction for J/psi -> pi+pi-pi0 is determined to be (2.137 +- 0.004 (stat.) +0.058-0.056 (syst.) +0.027-0.026 (norm.))*10-2, and the branching fraction for psi -> pi+pi-pi0 is measured as (2.14 +- 0.03 (stat.) +0.08-0.07 (syst.) +0.09-0.08 (norm.))*10-4. The J/psi decay is found to be dominated by an intermediate rho(770) state, whereas the psi decay is dominated by di-pion masses around 2.2 GeV/c2, leading to strikingly different Dalitz distributions.