arXiv subjects
Publications and source records attributed to BES collaboration.
Based on a sample of $58\times10^6J/ψ$ decays collected with the BESII detector at the BEPC, the $\barΛ$ decay parameter $α_{\barΛ}$ for $\barΛ\to \bar p π^+$ is measured using about 9000 $J/ψ\toΛ\barΛ\to p \bar p π^+π^-$ decays. A fit to the joint angular distributions yields $α_{\barΛ}(\barΛ\to \bar pπ^+)=-0.755\pm0.083\pm0.063$, where the first error is statistical, and the second systematic.
Using 58$\times 10^{6}$ $\jpsi$ events collected with the Beijing Spectrometer (BESII) at the Beijing Electron Positron Collider (BEPC), the branching fractions of $\jpsi$ to $p\bar{p}\eta$ and $p\bar{p}\etap$ are determined. The ratio $\frac{\Gamma(\jpsi\rar\ppb\eta)}{\Gamma(\jpsi\rar\ppb)}$ obtained by this analysis agrees with expectations based on soft-pion theorem calculations.
Radiative charmonium decays from the BESII sample of 14$\times10^{6}$ $ψ(2S)$-events into two different final states, $γK^+K^-$ and $γπ^+π^-$, are analyzed. Product branching fractions for $ψ(2S)\toγX\to γπ^+π^-$, $γK^+K^-$ are given, where $X=f_2(1270)$, $f_0(1500)$, and $f_0(1710)$ in $π^+π^-$ and $f_2(1270)$, $f_2'(1525)$, and $f_0(1700)$ in $K^+K^-$. An angular analysis gives the ratios of the helicity projections for the $f_2(1270)$ in $ψ(2S)\toγf_2(1270)\toγπ^+π^-$.
Rare decay modes $J/ψ\to D_{S}^{-} π^{+} + c.c.$, $J/ψ\to D^{-} π^{+} + c.c.$, and $J/ψ\to \bar D^{0} \bar K^{0} + c.c.$ are searched for using 5.77$\times 10^{7}$ $J/ψ$ events collected with the BESII detector at the BEPC. No signal above background is observed. We present upper limits on the branching fractions $B(J/ψ\to D_{S}^{-} π^{+})$ $<$ 1.4$\times10^{-4}$, $B(J/ψ\to D^{-} π^{+})$ $<7.5\times10^{-5}$, and $B(J/ψ\to \bar D^{0} \bar K^{0})$ $<$ 1.7$\times10^{-4}$ at the 90% confidence level.
Using 14 million psi(2S) events accumulated at the BESII detector, we report first measurements of branching fractions or upper limits for psi(2S) decays into gamma ppbar, gamma 2(pi^+pi^-), gamma K_s K^-pi^++c.c., gamma K^+ K^- pi^+pi^-, gamma K^{*0} K^- pi^+ +c.c., gamma K^{*0}\bar K^{*0}, gamma pi^+pi^- p pbar, gamma 2(K^+K^-), gamma 3(pi^+pi^-), and gamma 2(pi^+pi^-)K^+K^- with the invariant mass of hadrons below 2.9GeV/c^2. We also report branching fractions of psi(2S) decays into 2(pi^+pi^-) pi^0, omega pi^+pi^-, omega f_2(1270), b_1^\pm pi^\mp, and pi^0 2(pi^+pi^-) K^+K^-.
The lepton flavor violation processes $J/ψ\to μτ$ and $eτ$ are searched for using a sample of 5.8$\times 10^7$ $J/ψ$ events collected with the BESII detector. Zero and one candidate events, consistent with the estimated background, are observed in $J/ψ\to μτ, τ\to e\barν_eν_τ$ and $J/ψ\to eτ, τ\toμ\barν_μν_τ$ decays, respectively. Upper limits on the branching ratios are determined to be $Br(J/ψ\toμτ)<2.0 \times 10^{-6}$ and $Br(J/ψ\to eτ) < 8.3 \times10^{-6}$ at the 90% confidence level (C.L.).
Using $γγJ/ψ, J/ψ\ra e^+ e^-$ and $μ^+ μ^-$ events from a sample of $14.0\times 10^6$ $\psip$ decays collected with the BESII detector, the branching fractions for $\psip\ra π^0\J$, $η\J$, and $ψ(2S)\arγχ_{c1},γχ_{c2}\arγγ\jpsi$ are measured to be $B(\psip\ra π^0\J) = (1.43\pm0.14\pm0.13)\times 10^{-3}$, $B(\psip\ra η\J) = (2.98\pm0.09\pm0.23)%$, $B(ψ(2S)\arγχ_{c1}\arγγ\jpsi) = (2.81\pm0.05\pm 0.23)%$, and $B(ψ(2S)\arγχ_{c2}\arγγ\jpsi) = (1.62\pm0.04\pm 0.12)%$.