Search Results (69 total)

High-spin states of ¹⁵⁶Yb have been studied via the ¹⁴⁴Sm(¹⁶O,4n)¹⁵⁶Yb fusion-evaporation reaction at beam energy 102 MeV. The positive-parity yrast band and negative-parity cascade have been extended up to higher-spin states, respectively. In the present work, the negative-parity sequence above the 25^- state was found to be irregular and fragment into many parallel branches. This pattern may related to the excitation from the nucleon in the Z=64,N=82 core. The characteristics of alignment plot and E-GOS curve for the positive-parity yrast sequence in ¹⁵⁶Yb indicate that this nucleus may undergo an evolution from quasivibrational to quasirotational structure with increasing angular momentum. Based on a systematic summary of the available experimental alignments for the even-A ^{156,158,160,162,164}Yb isotopes, the structural evolutions induced by the increase in angular momentum, as well as by the change in neutron numbers, in these even-A Yb isotopes have been discussed in comparison with the cranked Woods-Saxon-Strutinsky calculations by means of total-Routhian-surface (TRS) methods.

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.

We report an uncertainty evaluation of an optical lattice clock based on the ¹S₀↔³P₀ transition in the bosonic isotope ¹⁷⁴Yb by use of magnetically induced spectroscopy. The absolute frequency of the ¹S₀↔³P₀ transition has been determined through comparisons with optical and microwave standards at NIST. The weighted mean of the evaluations is ν(¹⁷⁴Yb)=518  294  025  309  217.8(0.9)  Hz. The uncertainty due to systematic effects has been reduced to less than 0.8  Hz, which represents 1.5×10⁻¹⁵ in fractional frequency.

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.

Duration-controlled amplified spontaneous emission with an intensity of 10¹³  W∕cm² is used to convert a 7.5-μm-thick polyimide foil into a near-critical plasma, in which the p-polarized, 45-fs, 10¹⁹-W∕cm² laser pulse generates 3.8-MeV protons, emitted at some angle between the target normal and the laser propagation direction of 45°. Particle-in-cell simulations reveal that the efficient proton acceleration is due to the generation of a quasistatic magnetic field on the target rear side with magnetic pressure inducing and sustaining a charge separation electrostatic field.

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^-.

Measuring the luminescence of inserted sensing layers with high phosphorescent efficiency is an effective way of investigating the triplet exciton diffusion in nonemitting host materials. Researchers used to adopt simple models without taking the influence of doped layers into account. In this Brief Report, to include the dopant effects, a “double-layer” model is proposed for describing the exciton diffusion in doped and pure layers separately. The triplet diffusion lengths in Ir(ppy)₃-doped and pure 4,4^′-N,N^′-dicarbazole-biphenyl films are calculated to be 6.8 and 61.4 nm, respectively.

High-spin states in ¹⁸⁷Pt have been studied experimentally using the ¹⁷³Yb(¹⁸O, 4n) reaction at beam energies of 78 and 85 MeV. The previously known bands based on the νi_13/2,ν7/2^-[503], and νi_13/2²νj configurations have been extended to high-spin states, and new rotational bands associated with the ν3/2^-[512] and ν1/2^-[521] Nilsson orbits have been identified. The total Routhian surface calculations indicate that the transitional nucleus ¹⁸⁷Pt is very soft with respect to β and γ deformations. The band properties, such as level spacings, band crossing frequencies, alignment gains, and signature splittings, have been compared with the systematics observed in neighboring nuclei and have been interpreted within the framework of the cranked shell model. The rotational bands show different band crossing frequencies, which can be explained by the alignment either of i_13/2 neutrons or of h_9/2 protons. Importantly, evidence is presented for a πh_9/2 alignment at very low frequency in the ν7/2^-[503] band. The proton nature of the band crossing is strongly suggested by comparing the measured B(M1;I→I-1)/B(E2;I→I-2) ratios with the theoretical values from the semiclassical Dönau and Frauendof approach.

First-principles calculations have been conducted to investigate the magnetic properties of 3d and 4d transitional-metal (TM) atoms doped in hydrogen-passivated silicon quantum dots. The TM impurities exhibit almost identical magnetic behavior in the quantum dots of different sizes. The magnetic moments for most 3d and 4d TM atoms are completely quenched by the silicon hosts, while the magnitudes of the remaining moments for V, Cr, Mn, Nb, Mo, and Tc impurities are significantly reduced from those of free atoms. The moments of these 3d atoms are higher than those of the 4d atoms of the same family. Doping of TM atoms in different sites of lattice and the dopants of more than one atom are also considered. The structural and bonding properties of the TM-doped silicon quantum dots are discussed. The finding of magnetic properties makes them attractive for developing nanoscale magnetic species for spintronics.

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.

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.

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.

We analyze the nonlinear optical response of a six-level atomic system under a configuration of electromagnetically induced transparency. We show that the enhanced completely cross fifth-order nonlinearity generated in such a system can be used to produce efficient three-way entanglement and to realize a three-qubit quantum phase gate. We demonstrate that such phase gate can be transferred to an all-optical Toffoli gate, facilitating practical applications in quantum information and computation.

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 endohedral fullerene structures of medium-sized Si_N (30≤N≤39) clusters have been studied using the density functional theory (DFT) with gradient correction. For each cluster size, fullerene cages with different topologies and those filled by a different number of atoms were constructed. These cage isomers were then optimized by DFT-based molecular dynamic relaxations followed by numerical optimization. Compared with recent theoretical calculations [S. Yoo, J. J. Zhao, J. L. Wang, and X. C. Zeng, J. Am. Chem. Soc. 126, 13845 (2004)], the energies of the lowest-energy fullerene cage structures obtained here are lower for most clusters. In particular, the optimal filling and/or cage combination ratios for Si₃₇ and Si₃₈ were found to be Si₅@Si₃₂ and Si₆@Si₃₂, different from the previously proposed ones (Si₃@Si₃₄ and Si₄@Si₃₄).

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.