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J. Z. Bai

Publications and source records attributed to J. Z. Bai.

At least 217 records · Page 12Linked to original sources
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

Precise measurement of spin-averaged chi_{cJ}(1P) mass using photon conversions in psi(2S) -> gamma chi_{cJ}

Using photon conversions to e^+e^- pairs, the energy spectrum of inclusive photons from psi(2S) radiative decays is measured by BESII at the Beijing Electron-Positron Collider. The chi_{cJ}(1P) states (J=0,1,2) are clearly observed with energy resolution between 2.3 to 3.8 MeV, and their masses and the spin-averaged chi_{cJ} mass are determined to be M_{chi_{c0}}=3414.21\pm 0.39 \pm 0.27, M_{chi_{c1}}=3510.30\pm 0.14\pm 0.16, M_{chi_{c2}}=3555.70\pm 0.59 \pm 0.39 and M(^3P_{cog})=3524.85\pm 0.32 \pm 0.30 MeV/c^2.

hep-ex↗
arXiv2004

Measurements of J/psi --> p \bar{p}

The process J/ψ--> p \bar{p} is studied using 57.7 X 10^6 J/ψevents collected with the BESII detector at the Beijing Electron Positron Collider. The branching ratio is determined to be Br(J/ψ--> p \bar{p})=(2.26 +- 0.01 +- 0.14) X 10^{-3}, and the angular distribution is well described by \frac{dN}{d cosθ_p}=1+α\cos^2θ_p with α= 0.676 +- 0.036 +- 0.042, where θ_p is the angle between the proton and beam directions. The value of αobtained is in good agreement with the predictions of first-order QCD.

hep-ex↗
arXiv2004

Search for the Pentaquark State in $ψ(2S)$ and $J/ψ$ Decays to $K^0_SpK^-\bar n$ and $K^0_S\bar p K^+n$

Results are presented on $ψ(2S)$ and $J/ψ$ hadronic decays to $K^0_SpK^-\bar n$ and $K^0_S\bar p K^+n$ final states from data samples of 14 million $ψ(2S)$ and 58 million $J/ψ$ events accumulated at the BES II detector. No $Θ(1540)$ signal, the pentaquark candidate, is observed, and upper limits for ${\cal B}(ψ(2S)\toΘ\barΘ\to K^0_S p K^-\bar n + K^0_S \bar p K^+ n) < 0.84\times 10^{-5}$ and ${\cal B}(J/ψ\toΘ\barΘ\to K^0_S p K^-\bar n + K^0_S \bar p K^+ n) < 1.1\times 10^{-5}$ at the 90% confidence level are set. For single $Θ(1540)$ production, the upper limits determined by our analysis are also on the order of $10^{-5}$ in both $ψ(2S)$ and $J/ψ$ decays.

hep-ex↗
arXiv2004

Determination of BR(chi_{cJ} --> p \bar{p}) in psi(2S) decays

The processes psi(2S) --> gamma chi_{cJ}, chi_{cJ} --> p pbar (J=0,1,2) are studied using a sample of 14X10^6 psi(2S) decays collected with the Beijing Spectrometer at the Beijing Electron-Positron Collider. Very clear chi_{c0}, chi_{c1} and chi_{c2} signals are observed, and the branching fractions BR(chi_{cJ} --> p pbar) (J=0,1,2) are determined to be (27.1^{+4.3}_{-3.9}\pm 4.7)X10^{-5}, (5.7^{+1.7}_{-1.5}\pm0.9)X10^{-5}, and (6.5^{+2.4}_{-2.1}\pm1.0)X10^{-5}, respectively, where the first errors are statistical and the second are systematic.

hep-ex↗
arXiv2003

Search for K_S K_S in J/psi and psi(2S) decays

The CP violating processes J/psi-->K_S K_S and psi(2S)-->K_S K_S are searched for using samples of 58 million J/psi and 14 million psi(2S) events collected with the Beijing Spectrometer at the Beijing Electron Positron Collider. No signal is observed, and upper limits on the decay branching ratios are determined to be BR(J/psi-->K_S K_S) < 1.0x10^{-6} and BR(psi(2S)-->K_S K_S) < 4.6x10^{-6} at the 95% confidence level.

hep-ex↗
arXiv2003

Improved measurement of the branching ratio of J/psi-->K_S K_L

The branching ratio of J/psi-->K_S K_L is measured with improved precision to be B(J/psi-->K_S K_L) = (1.82\pm 0.04\pm 0.13)\times 10^{-4}. using J/psi data collected with the Beijing Spectrometer (BESII) at the Beijing Electron-Positron Collider. This result is used to test the perturbative QCD ``12%'' rule between psi(2S) and J/psi decays and to investigate the relative phase between the three-gluon and one-photon annihilation amplitudes in J/psi decays.

hep-ex↗
arXiv2003

First observation of psi(2S)-->K_S K_L

The decay psi(2S)-->K_S K_L is observed for the first time using psi(2S) data collected with the Beijing Spectrometer (BESII) at the Beijing Electron Positron Collider (BEPC); the branching ratio is determined to be B(psi(2S)-->K_S K_L) = (5.24\pm 0.47 \pm 0.48)\times 10^{-5}. Compared with J/psi-->K_S K_L, the psi(2S) branching ratio is enhanced relative to the prediction of the perturbative QCD ``12%'' rule. The result, together with the branching ratios of psi(2S) decays to other pseudoscalar meson pairs (π^+π^- and K^+K^-), is used to investigate the relative phase between the three-gluon and the one-photon annihilation amplitudes of psi(2S) decays.

hep-ex↗
arXiv2003

Measurement of Branching Ratios for $η_c$ Hadronic Decays

In a sample of 58 million $J/ψ$ events collected with the BES II detector, the process J/$ψ\toγη_c$ is observed in five decay channels: $η_c \to K^+K^-π^+π^-$, $π^+π^-π^+π^-$, $K^\pm K^0_S π^\mp$ (with $K^0_S\toπ^+π^-$), $ϕϕ$ (with $ϕ\to K^+K^-$) and $p\bar{p}$. From these signals, we determine $Br(J/ψ\toγη_c)\times Br(η_c\to K^+K^-π^+π^-)$ $=(1.5\pm0.2\pm0.2)\times10^{-4}$, $Br(J/ψ\toγη_c)\times Br(η_c\to π^+π^-π^+π^-)$ $=(1.3\pm0.2\pm0.4)\times10^{-4}$, $Br(J/ψ\toγη_c)\times Br(η_c\to K^\pm K_{S}^{0}π^\mp)$ $=(2.2\pm0.3\pm0.5)\times10^{-4}$, $Br(J/ψ\toγη_c)\times Br(η_c\to ϕϕ)$ $=(3.3\pm0.6\pm0.6)\times10^{-5}$ and $Br(J/ψ\toγη_c)\times Br(η_c\to p\bar{p})$ $=(1.9\pm0.3\pm0.3)\times10^{-5}$.

hep-ex↗
arXiv2003

Measurement of Inclusive Monmentum Spectra and Multiplicity Distributions of Charged Particles at $\sqrt{s}\sim 2-5$ GeV

Inclusive momentum spectra and multiplicity distributions of charged particles measured with BESII detector at center of mass energies of 2.2,2.6,3.0,3.2,4.6 and 4.8 GeV are presented. Values of the second binomial moment, $R_2$, obtained from the multiplicity distributions are reported. These results are compared with both experimental data from high energy $e^+e^-$, $ep$ and $p\bar{p}$ experiments and QCD calculations.

hep-ex↗
arXiv2003

Evidence of $κ$ particle in $J/ψ\to \bar{K}^*(892)^0 K^+ π^-$

Based on a $J/ψ$ data sample of $7.8 \times 10^6$ events at BESI, the decay of $ J/ψ\to \bar{K}^*(892)^0 K^+ π^-$ is studied and a low mass enhancement, which is believed not coming from the phase space effect or background, is visible in the $K^+ π^-$ invariant mass spectrum recoiling against $\bar{K}^*(892)^0$. Partial wave analysis of this channel favors this low mass enhancement being a broad $0^{+}$ resonance with the mass and width of $771^{+164}_{-221}\pm 55$ MeV/c$^2$ and $220^{+225}_{-169} \pm 97$ MeV/c$^2$, respectively.

hep-ex↗
arXiv2003

First Evidence of Lambda Lambda-bar in χ_cJ Decays

The first observation of χ_cJ (J=0,1,2) decays to Lambda Lambda-bar is reported using ψ(2S) data collected with the BESII detector at the BEPC. The branching ratios are determined to be BR(χ_c0 \to Lambda Lambda-bar) = (4.7^{+1.3}_{-1.2} \pm 1.0)\times 10^{-4}, BR(χ_c1 \to Lambda Lambda-bar) = (2.6^{+1.0}_{-0.9} \pm 0.6)\times 10^{-4} and BR(χ_c2 \to Lambda Lambda-bar) = (3.3^{+1.5}_{-1.3} \pm 0.7)\times 10^{-4}. Results are compared with model predictions.

hep-ex↗
arXiv2003

Search for Lepton Flavor Violation Process J/$ψ\to eμ$

Using a sample of 5.8X10E7 J/$ψ$ events, the Beijing Spectrometer experiment has searched for the decay J/$ψ\to eμ$. Four candidates, consistent with the estimated background, are observed, and an upper limit on the branching fraction of J/$ψ\to eμ$ of 1.1X10E-6 at the 90% C.L. is obtained.

hep-ex↗
arXiv2003

Observation of a near-threshold enhancement in th p pbar mass spectrum from radiative J/psi-->gamma p pbar decays

We observe a narrow enhancement near 2mp in the invariant mass spectrum of ppbar pairs from radiative J/psi-->gamma ppbar decays. The enhancement can be fit with either an S- or P-wave Breit Wigner fuction. In the case of the S-wave fit, the peak mass is below the 2mp threshold and the full width is less than 30 MeV. These mass and width values are not consistent with the properties of any known meson resonance.

hep-ex↗
arXiv2003

Measurements of the Mass and Full-Width of the $η_c$ Meson

In a sample of 58 million $J/ψ$ events collected with the BES II detector, the process J/$ψ\toγη_c$ is observed in five different decay channels: $γK^+K^-π^+π^-$, $γπ^+π^-π^+π^-$, $γK^\pm K^0_S π^\mp$ (with $K^0_S\toπ^+π^-$), $γϕϕ$ (with $ϕ\to K^+K^-$) and $γp\bar{p}$. From a combined fit of all five channels, we determine the mass and full-width of $η_c$ to be $m_{η_c}=2977.5\pm1.0 ({stat.})\pm1.2 ({syst.})$ MeV/$c^2$ and $Γ_{η_c} = 17.0\pm3.7 ({stat.})\pm7.4 ({syst.})$ MeV/$c^2$.

hep-ex↗
arXiv2003

Psi(2S) two- and three-body hadronic decays

We report measurements of branching fractions for psi(2S) decays into omega pi pi, b1 pi,omega f2(1270),omega KK, omega p pbar, phi pi pi, phi f0(980),phi KK, and an upper limit for phi p pbar final states based on a data sample of 4 X 10^6 psi(2S) events collected with the BESI detector at the Beijing Electron-Positron Collider. The branching fractions for b1 pi and omega f2(1270) update previous BES results, while those for other decay modes are first measurements. The ratios of psi(2S)and J/psi branching fractions are smaller than what is expected from the 12% rule by a factor of five for omega f2(1270),by a factor of two for omega pi pi, omega p pbar, and phi KK, while for other studied channels the ratios are consistent with expectation within errors.

hep-ex↗
arXiv2002

A Measurement of Psi(2S) Resonance Parameters

Cross sections for e+e- to hadons, pi+pi- J/Psi, and mu+mu- have been measured in the vicinity of the Psi(2S) resonance using the BESII detector operated at the BEPC. The Psi(2S) total width; partial widths to hadrons, pi+pi- J/Psi, muons; and corresponding branching fractions have been determined to be Gamma(total)= (264+-27) keV; Gamma(hadron)= (258+-26) keV, Gamma(mu)= (2.44+-0.21) keV, and Gamma(pi+pi- J/Psi)= (85+-8.7) keV; and Br(hadron)= (97.79+-0.15)%, Br(pi+pi- J/Psi)= (32+-1.4)%, Br(mu)= (0.93+-0.08)%, respectively.

hep-ph↗