Studies of Charmonium at BESIII

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 $\psi(3770)\to\gamma\eta_c(2S)$, the $\psi(3770)$ transition to $\chi_{cJ}$, isospin violation decay $\chi_{c0,2}\to\pi^0\eta_c$, the $C-$parity violation decays $J/\psi\to\gamma\gamma,\gamma\phi$ are searched for, but no significant signals are observed, and upper limits are set for these decays. The decays of $\psi(3770)\to\gamma\chi_{c1}$ and $J/\psi\to\pi^0\phi$ signals are observed. These measurements provide more information on the charmonium structure, and the isospin and $C$-parity violation in the charmonium decays.Comment: 8 pages, 4 figures, to be published in the proceedings of CHARM-2015, Detroit, MI, 18-22 May 201

Observation of Zc(3900)0Z_c(3900)^{0} in e+e−→π0π0J/ψe^+e^-\to\pi^0\pi^0 J/\psi

Using a data sample collected with the BESIII detector operating at the BEPCII storage ring, we observe a new neutral state $Z_c(3900)^{0}$ with a significance of $10.4\sigma$. The mass and width are measured to be $3894.8\pm2.3\pm3.2$ MeV/$c^2$ and $29.6\pm8.2\pm8.2$~MeV, respectively, where the first error is statistical and the second systematic. The Born cross section for $e^+e^-\to\pi^0\pi^0 J/\psi$ and the fraction of it attributable to $\pi^0 Z_c(3900)^{0}\to\pi^0\pi^0 J/\psi$ in the range $E_{cm}=4.19-4.42$ GeV are also determined. We interpret this state as the neutral partner of the four-quark candidate $Z_c(3900)^\pm$.Comment: 7 pages, 4 figures, submit to Physics Review Lette

Measurements of Absolute Branching Fractions of Fourteen Exclusive Hadronic DD Decays to η\eta

Using $2.93\,\rm fb^{-1}$ of $e^+e^-$ collision data taken at a center-of-mass energy of 3.773\,GeV with the BESIII detector, we report the first measurements of the absolute branching fractions of fourteen hadronic $D^{0(+)}$ decays to exclusive final states with an $\eta$, e.g., $D^0\to K^-\pi^+\eta$, $K^0_S\pi^0\eta$, $K^+K^-\eta$, $K^0_SK^0_S\eta$, $K^-\pi^+\pi^0\eta$, $K^0_S\pi^+\pi^-\eta$, $K^0_S\pi^0\pi^0\eta$, and $\pi^+\pi^-\pi^0\eta$; $D^+\to K^0_S\pi^+\eta$, $K^0_SK^+\eta$, $K^-\pi^+\pi^+\eta$, $K^0_S\pi^+\pi^0\eta$, $\pi^+\pi^+\pi^-\eta$, and $\pi^+\pi^0\pi^0\eta$. Among these decays, the $D^0\to K^-\pi^+\eta$ and $D^+\to K^0_S\pi^+\eta$ decays have the largest branching fractions, which are $\mathcal{B} (D^0\to K^-\pi^+\eta )=(1.853\pm0.025_{\rm stat}\pm0.031_{\rm syst})\%$ and $\mathcal{B}(D^+\to K^0_S\pi^+\eta)=(1.309\pm0.037_{\rm stat}\pm0.031_{\rm syst})\%$, respectively. We also determine the $CP$ asymmetries for the six decays with highest event yields. No evidence of $CP$ violation is found.Comment: 11 pages, 3 figure

Study of charmonium decays at BESIII

Based on the data samples collected at the energies of $J/\psi$, $\psi(3686)$, $\psi(3770)$ and $\psi(4040)$ resonances with the BESIII detector at the BEPCII storage ring, we present charmonium decays in two aspects. One is the search for baryonic decays of $\psi(3770)$ and $\psi(4040)$, including $\Lambda \bar\Lambda\pi^+\pi^-$, $\Lambda\bar\Lambda\pi^0$, $\Lambda \bar\Lambda\eta$, $\Sigma^+ \bar\Sigma^-$, $\Sigma^0 \bar\Sigma^0$, $\Xi^-\bar\Xi^+$ and $\Xi^0\bar\Xi^0$. None are observed, and upper limits are set at the 90% confidence level. The other is the light hadron spectroscopy from charmonium radiative decays, including the spin-parity analysis of the $p\bar p$ mass-threshold enhancement in $J/\psi$ radiative decays and the $\eta\eta$ system in $J/\psi\to\gamma\eta\eta$ radiative decays.Comment: to appear in the proceedings of The 6th International Workshop on Charm Physics (CHARM 2013

Study of the process e+e−→π0π0J/ψe^+e^-\to\pi^0\pi^0 J/\psi and neutral charmonium-like state Zc(3900)0Z_c(3900)^0

Cross sections of the process $e^+e^-\to\pi^0\pi^0 J/\psi$ at center-of-mass energies between 3.808 and 4.600 GeV are measured with high precision by using 12.4 $fb^{-1}$ of data samples collected with the BESIII detector operating at the BEPCII collider facility. A fit to the measured energy-dependent cross sections confirms the existence of the charmonium-like state $Y(4220)$. The mass and width of the $Y(4220)$ are determined to be $(4220.4\pm2.4\pm2.3)$ ${\rm MeV}/c^{2}$ and $(46.2\pm4.7\pm2.1)$ MeV, respectively, where the first uncertainties are statistical and the second systematic. The mass and width are consistent with those measured in the process $e^+e^-\to\pi^+\pi^- J/\psi$. The neutral charmonium-like state $Z_c(3900)^0$ is observed prominently in the $\pi^0 J/\psi$ invariant-mass spectrum, and, for the first time, an amplitude analysis is performed to study its properties. The spin-parity of $Z_c(3900)^0$ is determined to be $J^{P}=1^{+}$, and the pole position is $(3893.1\pm2.2\pm3.0)-i(22.2\pm2.6\pm7.0)$ ${\rm MeV}/c^2$, which is consistent with previous studies of electrically charged $Z_c(3900)^\pm$. In addition, cross sections of $e^+e^-\to\pi^0 Z_c(3900)^0\to \pi^0\pi^0 J/\psi$ are extracted, and the corresponding lineshape is found to agree with that of the $Y(4220)$.Comment: 8 pages, 3 figure

Measurements of the branching fractions for J/psi and psi(2S) -> Lambda Lambdabar pi0 and Lambda Lambdabar eta

We report on a study of the isospin-violating and conserving decays of the J/psi and psi(2S) charmonium state to Lambda Lambdabar pi0 and Lambda Lambdabar eta, respectively. The data are based on 225 million J/psi and 106 million psi(2S) events that were collected with the BESIII detector. The most accurate measurement of the branching fraction of the isospin-violating process J/psi ->Lambda Lambdabar pi0 is obtained, and the isospin-conserving processes J/psi ->Lambda Lambdabar eta and psi(2S) ->Lambda Lambdabar eta are observed for the first time. The branching fractions are measured to be B(J/psi ->Lambda Lambdabar pi0) = (3.78+-0.27stat)+-0.29sys)10^-5; B(J/psi ->Lambda Lambdabar eta) = (15.7+-0.79stat+-1.52sys)10^-5 and B(psi(2S) ->Lambda Lambdabar eta)= (2.47+-0.34stat+-0.19sys)10^-5. No significant signal events are observed for psi(2S) ->Lambda Lambdabar pi0 decay resulting in an upper limit of the branching fraction of B(psi(2S) ->Lambda Lambdabar pi0) < 0.29X10^-5 at the 90% confidence level. The two-body decay of J/psi-> Sigma(1385)^0 Lambdabar + c.c. is searched for, and the upper limit is B(J/psi-> Sigma(1385)^0 Lambdabar + c.c.) < 0.81X 10^-5 at the 90% confidence level

Search for a light CP-odd Higgs boson in the radiative decays of J/psi

We search for a light Higgs boson $A^0$ in the fully reconstructed decay chain of $J/\psi \rightarrow \gamma A^0$, $A^0 \rightarrow \mu^+\mu^-$ using $(225.0\pm2.8)\times10^6$ $J/\psi$ events collected by the BESIII experiment. The $A^0$ is a hypothetical CP-odd light Higgs boson predicted by many extensions of the Standard Model including two spin-0 doublets plus an extra singlet. We find no evidence for $A^0$ production and set $90\%$ confidence-level upper limits on the product branching fraction $\mathcal{B}(J/\psi \rightarrow \gamma A^0) \times \mathcal{B}(A^0 \rightarrow \mu^+\mu^-)$ in the range of $(2.8-495.3)\times 10^{-8}$ for $0.212 \le m_{A^0} \le 3.0$ GeV/c$^2$. The new limits are $5$ times below our previous results, and the nature of the $A^0$ is constrained to be mostly singlet.Comment: 7 pages, 5 figures, submitted to the Physical Review D (rapid communications

Determination of the number of J/ψ\psi events with J/ψ\psi \rightarrow decays

The number of $J/\psi$ events collected with the BESIII detector at the BEPCII from June 12 to July 28, 2009 is determined to be $(225.3\pm2.8)\times10^{6}$ using $J/\psi \rightarrow inclusive$ events, where the uncertainty is the systematic error and the statistical one is negligible.Comment: 12 pages, 14 figures; (the paper has been received by the Chinese Physics C.

Search for the rare decay of ψ(3686)→Λc+p‾e+e−+c.c.\psi(3686) \rightarrow \Lambda_c^+ \overline{p} e^+ e^- + c.c. at BESIII

Based on a data sample of $(448.1\pm2.9)\times10^6~\psi(3686)$ decays collected with the BESIII experiment, a search for the flavor changing neutral current transition $\psi(3686)\rightarrow \Lambda_c^+ \overline{p} e^+ e^- + c.c.$ is performed for the first time. No signal candidates are observed and the upper limit on the branching fraction of $\psi(3686)\rightarrow \Lambda_c^+ \overline{p} e^+ e^-$ is determined to be $1.7\times10^{-6}$ at the 90\% confidence level. The result is consistent with expectations from the Standard Model, and no evidence for new physics is found.Comment: 6 pages, 2 figures. Accepted by PR

First Observation of D+→ημ+νμD^+\to \eta\mu^+\nu_\mu and Measurement of its Decay Dynamics

By analyzing a data sample corresponding to an integrated luminosity of $2.93~\mathrm{fb}^{-1}$ collected at a center-of-mass energy of 3.773 GeV with the BESIII detector, we measure for the first time the absolute branching fraction of the $D^+\to \eta \mu^+\nu_\mu$ decay to be ${\mathcal B}_{D^+\to \eta \mu^+\nu_\mu}=(10.4\pm1.0_{\rm stat}\pm0.5_{\rm syst})\times 10^{-4}$. Using the world averaged value of ${\mathcal B}_{D^+\to \eta e^+\nu_e}$, the ratio of the two branching fractions is determined to be ${\mathcal B}_{D^+\to \eta \mu^+\nu_\mu}/{\mathcal B}_{D^+\to \eta e^+\nu_e}=0.91\pm0.13$, which agrees with the theoretical expectation of lepton flavor universality within uncertainty. Here, the uncertainty is the sum in quadrature of the statistical and systematic uncertainties. By studying the differential decay rates in five four-momentum transfer intervals, we obtain the product of the hadronic form factor $f^{\eta}_{+}(0)$ and the $c\to d$ Cabibbo-Kobayashi-Maskawa matrix element $|V_{cd}|$ to be $f_{+}^\eta (0)|V_{cd}|=0.087\pm0.008_{\rm stat}\pm0.002_{\rm syst}$. Taking the input of $|V_{cd}|$ from the global fit in the standard model, we determine $f_{+}^\eta (0)=0.39\pm0.04_{\rm stat}\pm0.01_{\rm syst}$. On the other hand, using the value of $f_+^{\eta}(0)$ calculated in theory, we find $|V_{cd}|=0.242\pm0.022_{\rm stat}\pm0.006_{\rm syst}\pm0.033_{\rm theory}$.Comment: 10 pages, 3 figure