arXiv subjects

BES Collaboration

Publications and source records attributed to BES Collaboration.

At least 55 records · Page 3Linked to original sources

arXiv2005

Observation of the decay $\psip\rar\kstark$

Using 14 million $ψ(2S)$ events collected with the BESII detector, branching fractions of $\psip\rar\kstarkpm$ and $\kstarknn$ are determined to be: $\calB(\psip\rar\kstarkpm)=(2.9^{+1.3}_{-1.7}\pm0.4)\times 10^{-5}$ and $\calB(\psip\rar\kstarknn)=(13.3^{+2.4}_{-2.7}\pm1.9)\times 10^{-5}$. The results confirm the violation of the "12%" rule for these two decay channels with higher precision. A large isospin violation between the charged and neutral modes is observed.

hep-ex↗

arXiv2005

Measurements of Cabibbo Suppressed Hadronic Decay Fractions of Charmed D0 and D+ Mesons

Using data collected with the BESII detector at $e^{+}e^{-}$ storage ring Beijing Electron Positron Collider, the measurements of relative branching fractions for seven Cabibbo suppressed hadronic weak decays $D^0 \to K^- K^+$, $π^+ π^-$, $K^- K^+ π^+ π^-$ and $π^+ π^+ π^- π^-$, $D^+ \to \bar{K^0} K^+$, $K^- K^+ π^+$ and $π^- π^+ π^+$ are presented.

hep-ex↗

arXiv2005

BESII Detector Simulation

A Monte Carlo program based on Geant3 has been developed for BESII detector simulation. The organization of the program is outlined, and the digitization procedure for simulating the response of various sub-detectors is described. Comparisons with data show that the performance of the program is generally satisfactory.

physics.ins-det↗

arXiv2005

Direct Measurement of the Pseudoscalar Decay Constant fD+

The absolute branching fraction of $D^+ \to μ^+ ν$ has been directly measured by an analysis of a data sample of about 33 ${\rm pb^{-1}}$ collected around $\sqrt{s}=3.773$ GeV with the BES-II at the BEPC. At these energies, $D^-$ meson is produced in pair as $e^+e^-\to D^{+} D^{-}$. A total of $5321 \pm 149 \pm 160$ $D^-$ mesons are reconstructed from this data set. In the recoil side of the tagged $D^-$ mesons, $2.67\pm1.74$ purely leptonic decay events of $D^+ \to μ^+ ν$ are observed. This yields a branching fraction of $BF(D^+ \to μ^+ ν_μ) = (0.122^{+0.111}_{-0.053}\pm 0.010)%$, and a corresponding pseudoscalar decay constant $f_{D^+}=(371^{+129}_{-119}\pm 25)$ MeV.

hep-ex↗

arXiv2004

Evidence of psi(3770) non-DD-bar Decay to J/psi pi+pi-

Evidence of $ψ(3770)$ decays to a non-${D \bar D}$ final state is observed. A total of $11.8 \pm 4.8 \pm 1.3$ $ψ(3770) \to \PPJP$ events are obtained from a data sample of 27.7 $\rm {pb^{-1}}$ taken at center-of-mass energies around 3.773 GeV using the BES-II detector at the BEPC. The branching fraction is determined to be $BF(ψ(3770) \to \PPJP)=(0.34\pm 0.14 \pm 0.09)%$, corresponding to the partial width of $Γ(ψ(3770) \to \PPJP) = (80 \pm 33 \pm 23)$ keV.

hep-ex↗

arXiv2004

Direct Measurement of the Branching Fraction for the Decay of $D^+ \to \bar K^0 e^+ν_e$ and Determination of $Γ(D^0 \to K^-e^+ν_e)/ Γ(D^+ \to \bar K^0 e^+ν_e)$

The absolute branching fraction for the decay $D^+ \to \bar K^0 e^+ν_e$ is determined using $5321\pm 149 \pm 160$ singly tagged $D^-$ sample from the data collected around 3.773 GeV with the BES-II detector at the BEPC collider. In the system recoiling against the singly tagged $D^-$ meson, $34.4\pm 6.1$ events for $D^+ \to \bar K^0 e ^+ν_e$ is observed. Those yield the absolute branching fraction to be $BF(D^+ \to \bar K^0 e^+ν_e)=(8.95 \pm 1.59\pm 0.67)%$. The ratio of the two partial widths for the decays of $D^0 \to K^-e^+ν_e$ and $D^+ \to \bar K^0 e ^+ν_e$ is determined to be $ Γ(D^0 \to K^-e^+ν_e)/ Γ(D^+ \to \bar K^0 e^+ν_e) = 1.08\pm 0.22 \pm 0.07$.

hep-ex↗

arXiv2004

Measurements of $ψ(2S)$ decays into $ϕπ^0$, $ϕη$, $ϕη^{'}$, $ωη$, and $ωη^{'}$

Decays of the $ψ(2S)$ into Vector plus Pseudoscalar meson final states have been studied with 14 million $ψ(2S)$ events collected with the BESII detector. Branching fractions of $ψ(2S) \rarϕη$, $ϕ\etap$, and $ω\etap$, and upper limits of $ψ(2S) \rar ϕ\piz$ and $ωη$ are obtained: $B(ψ(2S) \rarϕη) = (3.3\pm 1.1 \pm 0.5) \times 10^{-5}$, $B(ψ(2S) \rarϕ\etap) = (3.1\pm 1.4 \pm 0.7)\times 10^{-5}$, and $B(ψ(2S) \rarω\etap) = (3.2^{+2.4}_{-2.0} \pm 0.7) \times 10^{-5}$; and $B(ψ(2S) \rarϕ\piz) < 0.40 \times 10^{-5}$, and $B(ψ(2S) \rarωη) < 3.1 \times 10^{-5}$ at the 90 % C.L.. These results are used to test the pQCD ``12% rule''.

hep-ex↗

arXiv2004

Measurement of Cross Sections for $D^0 {\bar D}^0$ and $D^+D^-$ Production in $e^+e^-$ Annihilation at $\sqrt{s}=3.773$ GeV

The cross sections for $D^0 {\bar D}^0$ and $D^+D^-$ production at 3.773 GeV have been measured with BES-II detector at BEPC. These measurements are made by analyzing a data sample of about 17.3 $\rm pb^{-1}$ collected at the center-of-mass energy of 3.773 GeV. Observed cross sections for the charm pair production are radiatively corrected to obtain the tree level cross section for $D\bar D$ production. A measurement of the total tree level hadronic cross section is obtained from the tree level $D \bar D$ cross section and an extrapolation of the $R_{uds}$ below the open charm threshold.

hep-ex↗

arXiv2004

Observation of $\psp$ decays to $ρ(770)π$ and $ρ(2150)π$

\pspto ρπis observed for the fisrt time in a data sample of 14M \psp decays collected by the BESII detector at BEPC. The branching fraction is measured to be \BR(psptoρπ)=(5.1+-0.7+-0.8)10-5, where the first error is statistical and the second one is systematic. A high mass excited ρstate wirh mass around 2.15GeV/c2 is also observed wirh \BR(pspto ρ(2150)π) \ra pi+pi-pi0) =(19.4+-2.5+11.2-2.1)10-5. The branching fraction of \pspto pi+pi-pi0 is measued with improved precision, \BR(\pspto pi+pi-pi0)=(18.1+-1.8+-1.9)10-5. The results may shed light on the understanding of the longstanding "\rhopi puzzle" between \jpsi and \psp hadronic decays.

hep-ex↗

arXiv2004

First Measurement of the Branching Ratio of $J/ψ\toγf_{2}(1270) f_{2}(1270)$

Using 58 million $J/ψ$ events taken with the BES II detector at the Beijing Electron Positron Collider, a new decay mode $J/ψ\toγf_{2}(1270) f_{2}(1270) \to γπ^+π^-π^+π^-$ is observed for the first time. The branching ratio is determined to be $Br(J/ψ\toγf_{2}(1270) f_{2}(1270))=(9.5\pm0.7\pm1.6)\times 10^{-4}$, where the quoted errors are statistical and systematic, respectively.

hep-ex↗

arXiv2004

Observation of $K^(892)^0\bar K^(892)^0$ in $χ_{cJ}$ Decays

$K^*(892)^0\bar K^*(892)^0$ signals from $χ_{cJ} (J=0,1,2)$ decays are observed for the first time using a data sample of 14 million $ψ(2S)$ events accumulated at the BES II detector. The branching fractions ${\cal B}(χ_{cJ}\to K^*(892)^0\bar K^*(892)^0)$ $(J = 0,1,2)$ are determined to be $(1.55 \pm 0.35 \pm 0.30)\times 10^{-3}$, $(1.58 \pm 0.32 \pm 0.29)\times 10^{-3}$, and $(4.67 \pm 0.55 \pm 0.85)\times 10^{-3}$ for the $χ_{c0}$, $χ_{c1}$ and $χ_{c2}$ decays, respectively, where the first errors are statistical and the second are systematic. The significances of these signals are about 4.2$σ$, 4.3$σ$, and 7.5$σ$, respectively.

hep-ex↗

arXiv2004

Evidence for f0(980)f0(980) production in chi_c0 decays

Using a sample of 14 million $ψ(2S)$ events accumulated with the BES II detector, evidence for $f_0(980)f_0(980)$ production in $χ_{c0}$ decays is obtained for the first time; the branching ratio is determined to be ${\cal B}(χ_{c0}\to f_0(980)f_0(980)\toπ^+π^-π^+π^-) = (7.6 \pm 1.9 ({\rm stat}) \pm 1.6 ({\rm syst})) \times 10^{-4}$. The significance of the $f_0(980)$ signal is about 4.6$σ$.

hep-ex↗

arXiv2004

The $σ$ pole in $J/ψ\to ωπ^+ π^-$

Using a sample of 58 million $J/ψ$ events recorded in the BESII detector, the decay $J/ψ\to ωπ^+ π^-$ is studied. There are conspicuous $ωf_2(1270)$ and $b_1(1235)π$ signals. At low $ππ$ mass, a large broad peak due to the $σ$ is observed, and its pole position is determined to be $(541 \pm 39) $ - $i$ $(252 \pm 42)$ MeV from the mean of six analyses. The errors are dominated by the systematic errors.

hep-ex↗

arXiv2004

Direct Measurements of the Branching Fractions for $D^0 \to K^-e^+ν_e$ and $D^0 \to π^-e^+ν_e$ and Determinations of the Form Factors $f_{+}^{K}(0)$ and $f^π_{+}(0)$

The absolute branching fractions for the decays $D^0 \to K^-e ^+ν_e$ and $D^0 \to π^-e^+ν_e$ are determined using $7584\pm 198 \pm 341$ singly tagged $\bar D^0$ sample from the data collected around 3.773 GeV with the BES-II detector at the BEPC. In the system recoiling against the singly tagged $\bar D^0$ meson, $104.0\pm 10.9$ events for $D^0 \to K^-e ^+ν_e$ and $9.0 \pm 3.6$ events for $D^0 \to π^-e^+ν_e$ decays are observed. Those yield the absolute branching fractions to be $BF(D^0 \to K^-e^+ν_e)=(3.82 \pm 0.40\pm 0.27)%$ and $BF(D^0 \to π^-e^+ν_e)=(0.33 \pm 0.13\pm 0.03)%$. The vector form factors are determined to be $|f^K_+(0)| = 0.78 \pm 0.04 \pm 0.03$ and $|f^π_+(0)| = 0.73 \pm 0.14 \pm 0.06$. The ratio of the two form factors is measured to be $|f^π_+(0)/f^K_+(0)|= 0.93 \pm 0.19 \pm 0.07$.

hep-ex↗

arXiv2004

Observation of a threshold enhancement in the p \bar{Lambda} invariant mass spectrum

An enhancement near the m_p + M_Λ mass threshold is observed in the combined p \barΛ and \bar{p}Λinvariant mass spectrum from J/ψ--> p K^- \bar{Lambda} + c.c. decays. It can be fit with an S-wave Breit-Wigner resonance with a mass m = 2075 +- 12 (stat) +- 5 (syst) MeV and a width of Γ= 90 +- 35 (stat) +- 9 (syst) MeV; it can also be fit with a P-wave Breit-Wigner resonance. Evidence for a similar enhancement is also observed in ψ' --> p K^- \barΛ + c.c. decays. The analysis is based on samples of 5.8 X 10^7 J/ψand 1.4 X 10^7 ψ' decays accumulated in the BES II detector at the Beijing Electron-Positron Collider.

hep-ex↗

arXiv2004

A Study of J/psi-->gamma gamma V(rho,phi) Decays with the BESII Detector

Using a sample of $58\times 10^6$ $J/ψ$ events collected with the BESII detector, radiative decays $J/ψ\toγγV$, where $V=ρ$ or $ϕ$, are studied. A resonance around 1420 MeV/c$^2$ (X(1424)) is observed in the $γρ$ mass spectrum. Its mass and width are measured to be $1424\pm 10(stat)\pm 11(sys)$ MeV/c$^2$ and $ 101.0\pm 8.8 \pm 8.8$ MeV/c$^2$, respectively, and its branching ratio $B(J/ψ\to γX(1424)\to γγρ)$ is determined to be $(1.07\pm0.17 \pm 0.11)\times 10^{-4}$. A search for $X(1424)\to γϕ$ yields a 95% C.L. upper limit $B(J/ψ\to γX(1424)\to γγϕ) < 0.82 \times 10^{-4}$.

hep-ex↗

arXiv2004

Study of psi(2S) decays to X J/psi

Using J/psi -> mu^+ mu^- decays from a sample of approximately 4 million psi(2S) events collected with the BESI detector, the branching fractions of psi(2S) -> eta J/psi, pi^0 pi^0 J/psi, and anything J/psi normalized to that of psi(2S) -> pi^+ pi^- J/psi are measured. The results are B(psi(2S) -> eta J/psi)/B(psi(2S) -> pi^+ pi^- J/psi) = 0.098 \pm 0.005 \pm 0.010, B(psi(2S) -> pi^0 pi^0 J/psi)/B(psi(2S) -> pi^+ pi^- J/psi) = 0.570 \pm 0.009 \pm 0.026, and B(psi(2S) -> anything J/psi)/B(psi(2S) -> pi^+ pi^- J/psi) = 1.867 \pm 0.026 \pm 0.055.

hep-ex↗

arXiv2004

Evidence of $σ$ particle in $J/ψ\to ωππ$

Based on a sample of 7.8 million BESI $J/ψ$ events, the decay of $ J/ψ\to ωπ^+ π^-$ is studied. A low mass enhancement in the $π^+ π^-$ invariant mass spectrum recoiling against $ω$ particle is clearly seen which does not come from the phase space effect and the background. According to PWA analysis, this low mass enhancement is a broad $0^{++}$ resonance, the $σ$ particle. If a Breit-Winger function of constant width is used to fit the $σ$ signal, its mass and width are $384 \pm 66$ MeV and $458 \pm 100$ MeV respectively, which correspond to the pole position at (434 $\pm$ 78) - $i$ (202 $\pm$ 43) MeV.

hep-ex↗