In this work, we propose that detecting the polarization information of $chi_{cJ}to phiphi~(J=0,1,2)$ can be as good test of the role of hadronic loop effect on these decays. Our results shows that the obtained ratios of helicity amplitudes are quite
stable, which are $|F_{1,1}^{(0)}/F_{0,0}^{(0)}| approx 0.359$, $|F_{1,0}^{(1)}/F_{0,1}^{(1)}| =1$, $|F_{1,1}^{(1)}/F_{0,1}^{(1)}| =0$, $|F^{(2)}_{1,0}|/|F^{(2)}_{0,0}|=|F^{(2)}_{0,1}|/|F^{(2)}_{0,0}| approx 1.285,~|F^{(2)}_{1,-1}|/|F^{(2)}_{0,0}|=|F^{(2)}_{-1,1}|/|F^{(2)}_{0,0}| approx 5.110$ and $|F^{(2)}_{-1,-1}|/|F^{(2)}_{0,0}|=|F^{(2)}_{1,1}|/|F^{(2)}_{0,0}| approx 0.465$. By adopting these predicted ratios, we further generate Monte-Carlo events of moments $langle t_{ij} rangle$, which are directly related to the determination of helicity amplitudes. We suggest further experiments like BESIII and Belle II to perform an analysis on the polarizations of the $chi_{cJ}to phiphi$ process in the future, which is important to understand the underlying decay mechanism existing in $chi_{cJ}$ decays.
Measurements on the weak decay asymmetry parameters of charmed baryon, say $Xi_c$, provide more information on the $W$-emission and $W$-exchange mechanisms controlled by the strong and weak interactions. Taking advantage of the spin polarization in t
he charmed baryon decays, we investigate the possibility to measure the weak decay asymmetry parameters in the $e^{+}e^{-}to Xi_c^0barXi_c^0$ process. We analyze the transverse polarization spontaneously produced in this process and spin transfer in the subsequent $Xi_c$ decays. The sensitivity to measure the asymmetry parameters are estimated for the decay $Xi_ctoXi pi$.
We present a derivation of coherent helicity amplitudes for a particle decaying into multifinal states with nonzero spins. The results show that the coherent amplitudes introduce additional rotations to transform the helicities into a consistent heli
city system, which allows us to add helicity amplitudes for different decay chains coherently. These rotations may have significant effects on the interference between the decay chains in the partial wave analysis.
We propose to measure the decay asymmetry parameters in the hadronic weak decays of singly charmed baryons, such as $ldctoldpi^+,Sigma^0pi^+,p bar K_0$, $Xi_c^0toXi^-pi^+$ and $Omega_c^0toOmega^-pi^+$. The joint angular formulae for these processes a
re presented, and are used to extract the asymmetry parameters in $ee$ annihilation data. Base on the current $ldc$ data set collected at BESIII, we estimate the experimental sensitivities to measure the parameters $alpha_{ldpi^+}$ for $ldctoldpi^+$, $alpha_{Sigma^+pi^0}$ for $ldctoSigma^+pi^0$ and $alpha_{usigpi^+}$ for $ldctousigpi^+$.
To measure the $R$ value in an energy scan experiment with $ee$ collisions, precise calculation of initial state radiation is required in event generators. We present an event generator for this consideration, which incorporates initial state radiati
on effects up to the second order accuracy, and the radiative correction factor is calculated using the totally hadronic Born cross section. The measured exclusive processes are generated according to their cross sections, while the unknown processes are generated using the LUND Area Law model, and its parameters are tuned with data collected at $sqrt s=3.65$ GeV. The optimized values are validated with data in the range $sqrt s=2.2324sim3.671$ GeV. These optimized parameters are universally valid for event generation below the $Dbar D$ threshold.
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.
An exclusive event generator is designed for the $e^+e^-$ scan experiments with the initial state radiation effects up to the second order correction included. There are seventy hadronic decay modes available with the effective center-of-mass energy
coverage from the two pion mass threshold up to about 6 GeV. The achieved accuracy of initial state radiation correction reaches the level the generator KKMC achieved. The uncertainty associated with the calculation of correction factor to the initial state radiation is dominated by the measurements of the energy-dependence Born cross section. The generator is coded within the framework of BesEvtGen.
We investigate the decay and the production mechanism of the resonance X(1812) recently observed in the $jptogamma X(1812), X(1812)toomegaphi$ at BESII. The decay widths of $X(1812)toetaeta$,$ etaeta$,$ omegaphi$,$ K^+K^-$,$ rho^+rho^-$, $ omegaomega
$,$ K^{*+}K^{*-}$ and $pi^+pi^-$ are evaluated based on the scenario of the X(1812) as a candidate of $(ksks)$ molecule. It turns out that the quark exchange mechanism plays an important role in the understanding of the large decay width for the $X(1812)toomegaphi$. It is also found that the decay widths for $X(1812)toetaeta$ and $etaeta$ are enhanced by the quark exchange mechanism. These channels are suggested to be the tools to test the molecular scenario in experiment. The branching fraction of $Br(Xtoomegaphi)$ is evaluated to be about 4.60%. Searches for additional evidence about the X(1812) in $jp$ radiative decays are reviewed. In the molecular scenario, the X(1812) production rate is also evaluated to be $Gamma(jptogamma X)/Gamma(jptogamma K^{*+}K^{*-})=2.13^{+7.41}_{-1.85}$, which is close to the measured value $2.83pm0.92$.
