Search Results (126 total)

Using ψ(2S)→π⁺π^-J/ψ events in a sample of 14.0×10⁶ ψ(2S) decays collected with the BES-II detector, a search for the decay of the J/ψ to invisible final states is performed. No signal is found, and an upper limit at the 90% confidence level is determined to be 1.2×10^-2 for the ratio B(J/ψ→invisible) / B(J/ψ→μ⁺μ^-). This is the first search for J/ψ decays to invisible final states.

The decays of J/ψ→ηϕf₀(980)[η→γγ,ϕ→K⁺K^-,f₀(980)→π⁺π^-] are analyzed using a sample of 5.8×10⁷ J/ψ events collected with the BESII detector at the Beijing Electron-Positron Collider. A structure at around 2.18  GeV/c² with about 5σ significance is observed in the ϕf₀(980) invariant mass spectrum. A fit with a Breit-Wigner function gives the peak mass and width of m=2.186±0.010(stat)±0.006(syst)  GeV/c² and Γ=0.065±0.023(stat)±0.017(syst)  GeV/c², respectively, which are consistent with those of Y(2175), observed by the BABAR Collaboration in the initial-state radiation process e⁺e^-→γ_ISRϕf₀(980). The production branching ratio is determined to be Br(J/ψ→ηY(2175))Br(Y(2175)→ϕf₀(980))Br(f₀(980)→π⁺π^-)=[3.23±0.75(stat)±0.73(syst)]×  10^-4, assuming that the Y(2175) is a 1^-- state.

The decays of J/ψ→ωKK̅ π and J/ψ→ϕKK̅ π are studied using 5.8×10⁷ J/ψ events collected with the Beijing Spectrometer (BESII) at the Beijing Electron-Positron Collider (BEPC). The K_S⁰K^±π^∓ and K⁺K^-π⁰ systems, produced in J/ψ→ωKK̅ π, have enhancements in the invariant mass distributions at around 1.44  GeV/c². However, there is no evidence for mass enhancements in the KK̅ π system in J/ψ→ϕKK̅ π. The branching fractions of J/ψ→ωK_S⁰K^±π^∓, ϕK_S⁰K^±π^∓, ωK^*K̅ +c.c., and ϕK^*K̅ +c.c. are obtained, and the J/ψ→ηK_S⁰K^±π^∓ branching fraction is measured for the first time.

Using 58×10⁶ J/ψ events collected with the Beijing Spectrometer (BESII) at the Beijing Electron-Positron Collider, the decays J/ψ→γϕρ and J/ψ→γωρ are searched for, and upper limits on their branching fractions are reported at the 90% C.L. No clear structures are observed in the γρ, γϕ, or ρϕ mass spectra for J/ψ→γϕρ nor in the γρ, γω, or ρω mass spectra for J/ψ→γωρ.

By analyzing the data collected at the center-of-mass energy E_cm=3.773  GeV and below the DD̅ meson pair production threshold with the BES-II detector at the BEPC Collider, we directly measured the observed non-DD̅ cross section of ψ(3770) decay to be σ_{ψ(3770)→non-DD̅} ^obs=(0.95±0.35±0.29)  nb at E_cm=3.773  GeV, and the branching fraction BF[ψ(3770)→non-DD̅ ]=(13.4±5.0±3.6)% for inclusive non-DD̅ decay of ψ(3770). We also determined the cross section for DD̅ meson pair production to be σ_DD̅ ^obs=(6.12±0.37±0.23)  nb at E_cm=3.773  GeV.

Using 14.0×10⁶ψ(2S) events collected with the BES-II detector, the C-parity violating process J/ψ→γγ via ψ(2S)→π⁺π^-J/ψ is studied. We determine a new upper limit for the J/ψ→γγ branching ratio of B(J/ψ→γγ)<2.2×10^-5 at the 90% C.L., which is about 20 times lower than the previous measurement.

Using 58×10⁶ J/ψ and 14×10⁶ ψ(2S) events collected by the BESII detector at the BEPC, branching fractions or upper limits for the decays J/ψ and ψ(2S)→ΛΛ̅ π⁰ and ΛΛ̅ η are measured. For the isospin violating decays, the upper limits are determined to be B(J/ψ→ΛΛ̅ π⁰)<6.4×10^-5 and B[ψ(2S)→ΛΛ̅ π⁰]<4.9×10^-5 at the 90% confidence level. The isospin conserving process J/ψ→ΛΛ̅ η is observed for the first time, and its branching fraction is measured to be B(J/ψ→ΛΛ̅ η)=(2.62±0.60±0.44)×10^-4, where the first error is statistical and the second one is systematic. No ΛΛ̅ η signal is observed in ψ(2S) decays, and B[ψ(2S)→ΛΛ̅ η]<1.2×10^-4 is set at the 90% confidence level. Branching fractions of J/ψ decays into Σ⁺π^-Λ̅ and Σ̅ ^-π⁺Λ are also reported, and the sum of these branching fractions is determined to be B(J/ψ→Σ⁺π^-Λ̅ +c.c.)=(1.52±0.08±0.16)×10^-3.

Using 14×10⁶ ψ(2S) events accumulated at the BESII detector, we report first measurements of branching fractions or upper limits for ψ(2S) decays into γpp̅ , γ2(π⁺π^-), γK_S⁰K⁺π^-+c.c., γK⁺K^-π⁺π^-, γK^*0K^-π⁺+c.c., γK^*0K̅ ^*0, γπ⁺π^-pp̅ , γ2(K⁺K^-), γ3(π⁺π^-), and γ2(π⁺π^-)K⁺K^- with the invariant mass of hadrons below 2.9  GeV/c². We also report branching fractions of ψ(2S) decays into 2(π⁺π^-)π⁰, ωπ⁺π^-, ωf₂(1270), b₁^±π^∓, and π⁰2(π⁺π^-)K⁺K^-.

We report measurements of the continuum R_uds near the center-of-mass energy of 3.70 GeV, the R_{uds(c)+ψ(3770)}(s) and the R_had(s) values in e⁺e⁻ annihilation at 68 energy points in the energy region between 3.650 and 3.872 GeV with the BES-II detector at the BEPC Collider. We obtain the R_uds for the continuum light hadron (containing u, d, and s quarks) production near the DD̅ threshold to be R_uds=2.141±0.025±0.085.

Using 14M ψ(2S) events collected at BESII, the branching fraction of ψ(2S)→τ⁺τ^- is measured to be Br_ττ=(3.08±0.21±0.38)×10^-3, where the first error is statistical and the second is systematic.

Using a data sample of 58×10⁶ J/ψ decays collected with the Beijing Spectrometer II detector at the Beijing Electron Positron Collider, searches for invisible decays of η and η^′ in J/ψ to ϕη and ϕη^′ are performed. The ϕ signals, which are reconstructed in K⁺K^- final states, are used to tag the η and η^′ decays. No signals are found for the invisible decays of either η or η^′, and upper limits at the 90% confidence level are determined to be 1.65×10^-3 for the ratio B(η→invisible) / B(η→γγ) and 6.69×10^-2 for B(η^′→invisible) / B(η^′→γγ). These are the first searches for η and η^′ decays into invisible final states.

We calculate the one loop amplitudes for the two gluon scattering process in light cone gauge with fermions and scalars circulating in the loop. This extends the work of [D. Chakrabarti, J. Qiu, and C. B. Thorn, Phys. Rev. D 72, 065022 (2005)., D. Chakrabarti, J. Qiu, and C. B. Thorn, Phys. Rev. D 74, 045018 (2006)], in which only the gluon circulates the loop. By putting all fields in the adjoint representation with N_f=2, N_s=6, the scattering amplitude of gluon by gluon in the special case of N=4 super Yang-Mills can be obtained. The massive fermion and scalar with arbitrary representations are also considered.

A broad peak is observed at low K⁺K^- invariant mass in J/ψ→K⁺K^-π⁰ decays found in a sample of 5.8×10⁷ J/ψ events collected with the BESII detector. The statistical significance of the broad resonance is much larger than 5σ. A partial wave analysis shows that the J^PC of this structure is 1^--. Its pole position is determined to be [1576_-55⁺⁴⁹(stat)_-91⁺⁹⁸(syst)]  MeV/c²-i / 2[818_-23⁺²²(stat)_-133⁺⁶⁴(syst)]  MeV/c². These parameters are not compatible with any known meson resonances.

Radiative decays of the ψ(2S) into γKK̅ π and γηπ⁺π^- final states are studied using 14×10⁶ ψ(2S) events collected with the BESII detector. Branching fractions or upper limits on the branching fractions of ψ(2S) and χ_cJ decays are reported. No significant signal for η(1405)/η(1475) is observed in the KK̅ π or ηπ⁺π^- mass spectra, and upper limits on the branching fractions of ψ(2S)→γη(1405)/η(1475), η(1405)/η(1475)→KK̅ π, and ηπ⁺π^- are determined.

We measure the branching fractions for ψ(3770)→D⁰D̅ ⁰, D⁺D^-, DD̅ , and non-DD̅ to be (46.7±4.7±2.3)%, (36.9±3.7±2.8)%, (83.6±7.3±4.2)%, and (16.4±7.3±4.2)%, respectively. The resonance parameters of ψ(3770) and ψ(2S) are measured to be M_ψ(3770)=3772.2±0.7±0.3  MeV, Γ_ψ(3770)^tot=26.9±2.4±0.3  MeV, and Γ_ψ(3770)^ee=251±26±11  eV; M_ψ(2S)=3685.5±0.0±0.3  MeV, Γ_ψ(2S)^tot=331±58±2  keV, and Γ_ψ(2S)^ee=2.330±0.036±0.110  keV. We also measure the light hadron R value to be R_uds=2.262±0.054±0.109 in the energy region from 3.660 to 3.872 GeV.

We study the relative contribution of partonic subprocesses to D meson production and D meson-triggered inclusive di-hadrons to lowest order in perturbative QCD. While gluon fusion dominates the creation of large angle DD̅ pairs, charm on light parton scattering determines the yield of single inclusive D mesons. The distinctly different nonperturbative fragmentation of c quarks into D mesons versus the fragmentation of quarks and gluons into light hadrons results in a strong transverse momentum dependence of anticharm content of the away side charm-triggered jet. In p+A reactions, we calculate and resum the coherent nuclear-enhanced power corrections from the final-state partonic scattering in the medium. We find that single and double inclusive open charm production can be suppressed as much as the yield of neutral pions from dynamical high-twist shadowing. Effects of energy loss in p+A collisions are also investigated phenomenologically and may lead to significantly weaker transverse momentum dependence of the nuclear attenuation.

This is the second of a pair of articles on scattering of glue by glue,in which we give the light-cone gauge calculation of the one-loop on-shellhelicity conserving scattering amplitudes for gluon-gluon scattering (neglectingquark loops). The 1/p⁺ factors in the gluon propagatorare regulated by replacing p⁺ integrals with discretized sums omitting the p⁺=0 terms in each sum. We alsoemploy a novel ultraviolet regulator that is convenient for the light-coneworldsheet description of planar Feynman diagrams. The helicity conservingscattering amplitudes are divergent in the infrared. The infrared divergencesin the elastic one-loop amplitude are shown to cancel, in their contributionto cross sections, against ones in the cross section for unseen bremsstrahlunggluons. We include here the explicit calculation of the latter, because itassumes an unfamiliar form due to the peculiar way discretization of p⁺ regulates infrared divergences. In resolving the infrareddivergences we employ a covariant definition of jets, which allows a transparentdemonstration of the Lorentz invariance of our final results. Because we usean explicit cutoff of the ultraviolet divergences in exactly four spacetimedimensions, we must introduce explicit counterterms to achieve this finalcovariant result. These counterterms are polynomials in the external momentaof the precise order dictated by power counting. We discuss the modificationsthey entail for the light-cone worldsheet action that reproduces the bareplanar diagrams of the gluonic sector of QCD. The simplest way to do thisis to interpret the QCD string as moving in six spacetime dimensions.

The decay J/ψ→N̅ Nπ provides an effective isospin 1/2 filter for the πN system due to isospin conservation. Using 58×10⁶ J/ψ decays collected with the Beijing Electromagnetic Spectrometer at the Beijing Electron Positron Collider, more than 100 thousand J/ψ→pπ^-n̅ +c.c. events are obtained. Besides the two well-known N^* peaks at around 1500  MeV/c² and 1670  MeV/c², there are two new, clear N^* peaks in the pπ invariant mass spectrum around 1360  MeV/c² and 2030  MeV/c² with statistical significance of 11σ and 13σ, respectively. We identify these as the first direct observation of the N^*(1440) peak and a long-sought missing N^* peak above 2  GeV/c² in the πN invariant mass spectrum.

Using 14×10⁶ ψ(2S) events collected with the Beijing Spectrometer (BESII) at the Beijing Electron-Positron Collider, the branching fractions of ψ(2S) decays to pn̅ π^- and p̅ nπ⁺ and the branching fractions of the main background channels ψ(2S)→pn̅ π^-π⁰, ψ(2S)→γχ_c0→γpn̅ π^-, ψ(2S)→γχ_c2→γpn̅ π^-, and ψ(2S)→γχ_cJ→γpn̅ π^-π⁰ are determined. The contributions of the N^* resonances in ψ(2S)→pn̅ π^-+c.c. are also discussed.

The decay channel J/ψ→γωω, ω→π⁺π^-π⁰ is analyzed using a sample of 5.8×10⁷ J/ψ events collected with the BESII detector. The ωω invariant mass distribution peaks at 1.76  GeV/c², just above the ωω threshold. Analysis of angular correlations indicates that the ωω system below 2  GeV/c² is predominantly pseudoscalar. A partial wave analysis confirms the predominant pseudoscalar structure, together with small 0⁺⁺ and 2⁺⁺ contributions, and yields a pseudoscalar mass M=1744±10 (stat)±15 (syst)  MeV/c², a width Γ=244_-21⁺²⁴ (stat)±25 (syst)  MeV/c², and a product branching fraction Br(J/ψ→γη(1760))·Br(η(1760)→ωω)=(1.98±0.08 (stat)±0.32 (syst))×10^-3.

An enhancement near threshold is observed in the ωϕ invariant mass spectrum from the doubly Okubo-Zweig-Iizuka–suppressed decays of J/ψ→γωϕ, based on a sample of 5.8×10⁷ J/ψ events 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_-26⁺¹⁹(stat)±18(syst)  MeV/c² and Γ=105±20(stat)±28(syst)  MeV/c². The product branching fraction is determined to be B(J/ψ→γX)B(X→ωϕ)=[2.61±0.27(stat)±0.65(syst)]×10^-4.

The decay modes J/ψ→γπ⁰, γη and γη^′ are analyzed using a data sample of 58×10⁶ J/ψ decays collected with the BESII detector at the BEPC. The branching fractions are determined to be: Br(J/ψ→γπ⁰)=(3.13_-0.47^+0.65)×10^-5, Br(J/ψ→γη)=(11.23±0.89)×10^-4, and Br(J/ψ→γη^′)=(5.55±0.44)×10^-3, where the errors are combined statistical and systematic errors. The ratio of partial widths Γ(J/ψ→γη^′)/Γ(J/ψ→γη) is measured to be 4.94±0.40, and the singlet-octet pseudoscalar mixing angle of η-η^′ system is determined.

Based on 5.8×10⁷J/ψ events collected with BESII at the Beijing Electron-Positron Collider (BEPC), the decay branching fractions of J/ψ→ωπ⁰, ωη, and ωη^′ are measured using different η and η^′ decay modes. The results are higher than previous measurements. The ωπ⁰ electromagnetic form factor is also obtained.

Using χ_cJ→2(π⁺π^-)pp̅ decays from 14×10⁶ψ(2S) events accumulated by the BESII detector at the BEPC, the intermediate states Ξ^-Ξ̅ ⁺, ΛΛ̅ π⁺π^-, and K_S⁰K_S⁰pp̅ are studied, and their branching ratios or upper limits are measured.