Searcharxiv⌕ Search

arXiv subjects

BES Collaboration

Publications and source records attributed to BES Collaboration.

At least 37 records · Page 2Linked to original sources
arXiv2006

Production of $σ$ in $ψ(2S)\to π^{+}π^{-}J/ψ$

Using 14M $ψ(2S)$ events accumulated by BESII at the BEPC, a Covariant Helicity Amplitude Analysis is performed for $ψ(2S)\toπ^+π^-J/ψ, J/ψ\to μ^+μ^-$. The $π^+π^-$ mass spectrum, distinctly different from phase space, suggests $σ$ production in this process. Two different theoretical schemes are used in the global fit to the data. The results are consistent with the existence of the $σ$. The $σ$ pole position is determined to be $(552^{+84}_{-106})-i(232^{+81}_{-72})$ MeV/$c^2$.

hep-ex↗
arXiv2006

Search for Invisible Decays of $η$ and $η^\prime$ in $J/ψ\to ϕη$ and $ϕη^\prime$

Using a data sample of $58\times 10^6$ $J/ψ$ decays collected with the BES II detector at the BEPC, searches for invisible decays of $η$ and $η^\prime$ in $J/ψ$ to $ϕη$ and $ϕη^\prime$ are performed. The $ϕ$ signals, which are reconstructed in $K^+K^-$ final states, are used to tag the $η$ and $η^\prime$ decays. No signals are found for the invisible decays of either $η$ or $η^\prime$, and upper limits at the 90% confidence level are determined to be $1.65 \times 10^{-3}$ for the ratio $\frac{B(η\to \text{invisible})}{B(η\toγγ)}$ and $6.69\times 10^{-2}$ for $\frac{B(η^\prime\to \text{invisible})}{B(η^\prime\toγγ)}$. These are the first searches for $η$ and $η^\prime$ decays into invisible final states.

hep-ex↗
arXiv2006

Measurement of χ_cJ--> K+K-K+K-

Using 14M psi(2S) events taken with the BES-II detector, chi_cJ-->K+K-K+K- decays are studied. For the four-kaon final state, the branching fractions are B(chi_c0,1,2 -->K+K-K+K-)=(3.48\pm 0.23\pm 0.47)\times 10^{-3}, (0.70\pm 0.13\pm 0.10)\times 10^{-3}, and (2.17\pm 0.20\pm 0.31)\times 10^{-3}. For the ϕK+K- final state, the branching fractions, which are measured for the first time, are B(chi_c0,1,2-->ϕK+K-)=(1.03\pm 0.22\pm 0.15)\times 10^{-3}, (0.46\pm 0.16\pm 0.06)\times 10^{-3}, and (1.67\pm 0.26\pm 0.24)\times 10^{-4}. For the ϕϕfinal state, B(chi_{c0,2}-->ϕϕ)=(0.94\pm 0.21\pm 0.13)\times 10^{-3} and (1.70\pm 0.30\pm 0.25)\times 10^{-3}.

hep-ex↗
arXiv2006

Observation of Two New N* Peaks in J/psi -> $p pi^- \bar n$ and $\bar pπ^+n$ Decays

The $πN$ system in decays of $J/ψ\to\bar NNπ$ is limited to be isospin 1/2 by isospin conservation. This provides a big advantage in studying $N^*\to πN$ compared with $πN$ and $γN$ experiments which mix isospin 1/2 and 3/2 for the $πN$ system. Using 58 million $J/ψ$ decays collected with the Beijing Electron Positron Collider, more than 100 thousand $J/ψ\to p π^- \bar n + c.c.$ events are obtained. Besides two well known $N^*$ peaks at 1500 MeV and 1670 MeV, there are two new, clear $N^*$ peaks in the $pπ$ invariant mass spectrum around 1360 MeV and 2030 MeV. They are the first direct observation of the $N^*(1440)$ peak and a long-sought "missing" $N^*$ peak above 2 GeV in the $πN$ invariant mass spectrum. A simple Breit-Wigner fit gives the mass and width for the $N^*(1440)$ peak as $1358\pm 6 \pm 16$ MeV and $179\pm 26\pm 50$ MeV, and for the new $N^*$ peak above 2 GeV as $2068\pm 3^{+15}_{-40}$ MeV and $165\pm 14\pm 40$ MeV, respectively.

hep-ex↗
arXiv2006

First observation of $ψ(2S) \to p \bar{n} π^- +c.c.$

Using 14 million $ψ(2S)$ events collected with the Beijing Spectrometer (BESII) at the Beijing Electron-Positron Collider, the branching fractions of $ψ(2S)$ decays to $p \bar{n} π^-$ and $\bar{p} n π^+$ and the branching fractions of the main background channels $ψ(2S) \to p \bar{n} π^-π^0$, $ψ(2S) \to γχ_{c0} \to γp \bar{n} π^-$, $ψ(2S) \to γχ_{c2} \to γp \bar{n} π^-$, and $ψ(2S) \to γχ_{cJ} \to γp \bar{n} π^- π^0$ are determined. The contributions of the $N^{\ast}$ resonances in $ψ(2S) \to p \bar{n} π^- +c.c.$ are also discussed.

hep-ex↗
arXiv2006

Observation of a broad 1^-- resonant structure around 1.5 GeV/$c^2$ in the K^+K^- mass spectrum in J/psi --> K^+K^-pi^0

A broad peak is observed at low K^+K^- invariant mass in J/psi --> K^+K^-pi^0 decays found in a sample of 5.8\times 10^7 J/psi events collected with the BESII detector. A partial wave analysis shows that the J^PC of this structure is 1^--. Its pole position is determined to be (1576^{+49}_{-55}(stat)^{+98}_{-91}(syst)) MeV/c^2 - i(409^{+11}_{-12}$(stat)^{+32}_{-67}(syst)) MeV/c^2. These parameters are not compatible with any known meson resonances.

hep-ex↗
arXiv2006

Measurements of the absolute branching fractions for D->Kbar pi e+ nu_e, D-> K*bar e+nu_e and determination of Gamma(D+ -> K*0bar e+ nu_e)/Gamma(D+ -> K0bar e+nu_e)

Using the data of about 33 pb$^{-1}$ collected at and around 3.773 GeV with the BES-II detector at the BEPC collider, we have studied the exclusive semileptonic decays $D^+ \to K^-π^+ e^+ν_e$, $D^0 \to \bar K^0π^-e^+ν_e$, $D^+ \to \bar K^{*0}e^+ν_e$ and $D^0 \to K^{*-}e^+ν_e$. The absolute branching fractions for the decays are measured to be ${BF}(D^+ \to K^-π^+e^+ν_e)=(3.50\pm0.75\pm0.27)%$, ${BF}(D^0 \to \bar K^0π^-e^+ν_e)=(2.61\pm1.04\pm0.28)%$, ${BF}(D^+ \to \bar K^{*0}e^+ν_e)=(5.06\pm1.21\pm0.40)%$ and ${BF}(D^0 \to K^{*-}e^+ν_e)=(2.87\pm 1.48\pm 0.39)%$. The ratio of the vector to pseudoscalar semileptonic decay rates $Γ(D^+\to\bar K^{*0}e^+ν_e)/Γ(D^+\to\bar K^0e^+ν_e)$ is determined to be $0.57\pm0.17\pm0.02$.

hep-ex↗
arXiv2006

Observation of a near-threshold enhancement in the ωϕmass spectrum from the doubly OZI suppressed decay J/ψ\to γωϕ

An enhancement near threshold is observed in the ωϕinvariant mass spectrum from the doubly OZI suppressed decays of J/ψ\to γωϕ, based on a sample of 5.8 X 10^7 J/ψevents collected with the BESII detector. A partial wave analysis shows that this enhancement favors J^P = 0^+, and its mass and width are M = 1812^{+19}_{-26} (stat) +- 18 (syst) MeV/c^2 and Γ= 105+-20 (stat) +- 28$ (syst) MeV/c^2. The product branching fraction is determined to be B(J/ψ\to γX) B(X\toωϕ) = (2.61 +- 0.27 (stat) +- 0.65$ (syst)) X 10^{-4}.

hep-ex↗
arXiv2006

Search for the Rare Decays J/Psi --> Ds- e+ nu_e, J/Psi --> D- e+ nu_e, and J/Psi --> D0bar e+ e-

We report on a search for the decays J/Psi --> Ds- e+ nu_e + c.c., J/Psi --> D- e+ nu_e + c.c., and J/Psi --> D0bar e+ e- + c.c. in a sample of 5.8 * 10^7 J/Psi events collected with the BESII detector at the BEPC. No excess of signal above background is observed, and 90% confidence level upper limits on the branching fractions are set: B(J/Psi --> Ds- e+ nu_e + c.c.)<4.8*10^-5, B(J/Psi --> D- e+ nu_e + c.c.)<1.2*10^-5, and B(J/Psi --> D0bar e+ e- + c.c.)<1.1*10^-5

hep-ex↗
arXiv2006

Experimental study of $ψ(2S)$ decays to $\K^+ K^- π^+ π^- π^0$ final states

$K^+K^-π^+π^-π^0$ final states are studied using a sample of $14\times10^6$ $ψ(2S)$ decays collected with the Beijing Spectrometer (BESII) at the Beijing Electron-Position Collider. The branching fractions of $ψ(2S)$ decays to $ K^+K^-π^+π^-π^0$, $ωK^+ K^-$, $ωf_0(1710)$, $ K^{\ast}(892)^0 K^- π^+π^0+c.c.$, $K^{\ast}(892)^{+} K^- π^+π^- +c.c.$, $K^{\ast}(892)^{+} K^- ρ^0+c.c.$ and $K^{\ast}(892)^0 K^-ρ^+ + c.c.$ are determined. The first two agree with previous measurements, and the last five are first measurements.

hep-ex↗
arXiv2005

Measurement of branching fractions for the inclusive Cabibbo-favored ~K*0(892) and Cabibbo-suppressed K*0(892) decays of neutral and charged D mesons

The branching fractions for the inclusive Cabibbo-favored ~K*0 and Cabibbo-suppressed K*0 decays of D mesons are measured based on a data sample of 33 pb-1 collected at and around the center-of-mass energy of 3.773 GeV with the BES-II detector at the BEPC collider. The branching fractions for the decays D+(0) -> ~K*0(892)X and D0 -> K*0(892)X are determined to be BF(D0 -> K*0X) = (8.7 +/- 4.0 +/- 1.2)%, BF(D+ -> ~K*0X) = (23.2 +/- 4.5 +/- 3.0)% and BF(D0 -> K*0X) = (2.8 +/- 1.2 +/- 0.4)%. An upper limit on the branching fraction at 90% C.L. for the decay D+ -> K*0(892)X is set to be BF(D+ -> K*0X) < 6.6%.

hep-ex↗
arXiv2005

Measurement of the branching fractions for $J/ψ\toγπ^0$, $γη$ and $γη^{\prime}$

The decay modes $\jpsi\arγπ^0, γη$ and $γ\etap$ are analyzed using a data sample of 58 million $\jpsi$ decays collected with the BESII detector at BEPC. The branching fractions are determined to be: $Br(\jpsi\arγπ^0)=(3.13^{+0.65}_{-0.44})\times10^{-5}$, $Br(\jpsi\arγη)=(11.23\pm0.89)\times10^{-4}$, and $Br(\jpsi\arγ\etap)=(5.55\pm0.44)\times10^{-3}$, where the errors are combined statistical and systematic errors. The ratio of partial widths $Γ(\jpsi\arγ\etap)/Γ(\jpsi\arγη)$ is measured to be $4.94\pm0.40$, and the singlet-octet pseudoscalar mixing angle of $η-\etap$ system is determined to be $θ_{P}=(-22.08\pm0.81)^{\circ}$.

hep-ex↗
arXiv2005

Partial Wave Analysis of $χ_{c0}\toπ^+π^-K^+K^-$

A partial wave analysis of $χ_{c0}\toπ^+π^-K^+K^-$ in $ψ(2S)\toγχ_{c0}$ decay is presented using a sample of 14 million $ψ(2S)$ events accumulated by the BES II detector. The data are fitted to the sum of relativistic covariant tensor amplitudes for intermediate resonant decay modes. From the fit, significant contributions to $χ_{c0}$ decays from the channels $f_0(980)f_0(980)$, $f_0(980)f_0(2200)$, $f_0(1370)f_0(1710)$, $K^*(892)^0\bar K^*(892)^0$, $K^*_0(1430)\bar K^*_0(1430)$, $K^*_0(1430)\bar K^*_2(1430) + c.c.$, and $K_1(1270)K$ are found. Flavor-SU(3)-violating $K_1(1270)-K_1(1400)$ asymmetry is observed. Values obtained for the masses and widths of the resonances $f_0(1710)$, $f_0(2200)$, $f_0(1370)$, and $K^*_0(1430)$ are presented.

hep-ex↗
arXiv2005

Observation of a resonance X(1835) in J/ψ--> γπ^+ π^- η^{\prime}

The decay channel J/ψ--> γπ^+ π^- η^{\prime} is analyzed using a sample of 5.8\times 10^7 Jψevents collected with the BESII detector. A resonance, the X(1835), is observed in the π^+ π^- η^{\prime} invariant mass spectrum with a statistical significance of 7.7 σ. A fit with a Breit-Wigner function yields a mass M = 1833.7 \pm 6.1(stat) \pm 2.7(syst) MeV/c^2, a width Γ= 67.7 \pm 20.3(stat) \pm 7.7(syst) MeV/c^2 and a product branching fraction B(J/ψ--> γX) B(X --> π^+ π^- η^{\prime}) = (2.2 \pm 0.4(stat) \pm 0.4(syst)) \times 10^{-4}. The mass and width of the X(1835) are not compatible with any known meson resonance. Its properties are consistent with expectations for the state that produces the strong p\bar{p} mass threshold enhancement observed in the Jψ-->γp \bar{p} process at BESII.

hep-ex↗
arXiv2005

Obervation of χ_{cJ}--> omega omega decays

Decays of $χ_{c0,2}\ar\ww$ are observed for the first time using a sample of $14.0\times 10^6$ $ψ(2S)$ events collected with the BESII detector. The branching ratios are determined to be ${\cal B}(χ_{c0}\ar \ww)=(2.29\pm 0.58\pm 0.41)\times 10^{-3}$ and ${\cal B}(χ_{c2}\ar\ww)=(1.77\pm 0.47\pm 0.36)\times 10^{-3}$, where the first errors are statistical and the second systematic. The significances of the two signals are $4.4σ$ and $4.7σ$, respectively.

hep-ex↗
arXiv2005

First Measurements of eta_c Decaying into K^+K^-2(pi^+pi^-) and 3(pi^+pi^-)

The decays of eta_c to K^+K^-2(pi^+pi^-) and 3(pi^+pi^-) are observed for the first time using a sample of 5.8X10^7 J/ψevents collected by the BESII detector. The product branching fractions are determined to be B(J/ψ-->gamma eta_c)*B(eta_c-->K^+K^-pi^+pi^-pi^+pi^-)=(1.21+-0.32+- 0.23)X10^{-4}$,B(J/ψ-->gamma eta_c)*B(eta_c-->K^{*0}\bar{K}^{*0}pi^+pi^-)= (1.29+-0.43+-0.32)X10^{-4}$, and (J/ψ-->gamma eta_c)* B(eta_c-->pi^+pi^-pi^+pi^-pi^+pi^-)= (2.59+-0.32+-0.48)X10^{-4}. The upper limit for eta_c-->phi pi^+pi^-pi^+pi^- is also obtained as B(J/ψ-->gamma eta_c)*B(eta_c--> phi pi^+pi^-pi^+pi^-)< 6.03 X10^{-5} at the 90% confidence level.

hep-ex↗