Exclusive event generator for $e^+e^-$ scan experiments

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.

Precision measurements of branching fractions for $ psitopi^0 Jpsi$ and $eta Jpsi$

We present a precision study of the $psiptopi^0 J/psi$ and $eta J/psi$ decay modes. The measurements are obtained using $106times10^6$ $psi$ events accumulated with the BESIII detector at the BEPCII $ee$ collider operating at a center-of-mass energy corresponding to the $psip$ mass. We obtain $mathcal{B}(psiptopi^0 J/psi)=(1.26pm0.02{rm (stat.)}pm0.03{rm (syst.)})times 10^{-3}$ and $mathcal{B}(psiptoeta J/psi)=(33.75pm0.17{rm (stat.)}pm0.86{rm (syst.)})times 10^{-3}$. The branching fraction ratio $R=frac{mathcal{B}(psiptopi^0 J/psi)}{mathcal{B}(psiptoeta J/psi)}$ is determined to be $(3.74pm0.06 {rm(stat.)}pm0.04 {rm(syst.)})times 10^{-2}$. The precision of these measurements of $mathcal{B}(psiptopi^{0} J/psi)$ and $R$ represent a significant improvement over previously published values.

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 $chi_{c1}$ decays into vector meson pairs $phiphi$, $omegaomega$, and $omegaphi$

Decays of $chi_{c1}$ to vector meson pairs $phiphi$, $omegaomega$ and $omegaphi$ are observed for the first time using $(106pm4)times 10^6$ $psip$ events accumulated at the BESIII detector at the BEPCII $e^+e^-$ collider. The branching fractions are measured to be $(4.4pm 0.3pm 0.5)times 10^{-4}$, $(6.0pm 0.3pm 0.7)times 10^{-4}$, and $(2.2pm 0.6pm 0.2)times 10^{-5}$, for $chi_{c1}to phiphi$, $omegaomega$, and $omegaphi$, respectively. The observation of $chi_{c1}$ decays into a pair of vector mesons $phiphi$, $omegaomega$ and $omegaphi$ indicates that the hadron helicity selection rule is significantly violated in $chi_{cJ}$ decays. In addition, the measurement of $chi_{cJ}to omegaphi$ gives the rate of doubly OZI-suppressed decay. Branching fractions for $chi_{c0}$ and $chi_{c2}$ decays into other vector meson pairs are also measured with improved precision.

Recent Results From BESII

We present recent results from the BES experiment on the observation of the Y(2175) in $J/psito phi f_0(980) eta$, and $eta(2225)$ in $J/psito gamma phi phi$, and X(1440) in $J/psi$ hadronic decays, together with the new observation of $psi(2S)$ radiative decays and hadronic decays into $nksldb+c.c., ldldbpi^0, ldldbeta$. The effort to search for $J/psi$ decays into $gammagamma$ and invisible decays are also reported.