We observe a narrow enhancement near 2m(p) in the invariant mass spectrum of pp pairs from radiative J/psi-->gammapp decays. No similar structure is seen in J/psi-->pi(0)pp decays. The results are based on an analysis of a 58 x 10(6) event sample of J/psi decays accumulated with the BESII detector at the Beijing electron-positron collider. The enhancement can be fit with either an S- or P-wave Breit-Wigner resonance function. In the case of the S-wave fit, the peak mass is below 2m(p) at M=1859(+3)(-10) (stat)+5-25(syst) MeV/c(2) and the total width is Gamma<30 MeV/c(2) at the 90% confidence level. These mass and width values are not consistent with the properties of any known particle.
We consider a laser model consisting of a single four-level or three-level atom, an optical cavity, and an incoherent pump. Results for photon statistics for varying pump levels are obtained using a quantum trajectory algorithm. In particular, we calculate the mean photon number, Fano factor ͑which is the variance over the mean͒. We examine that the behavior of the single-atom device as , the fraction of spontaneous emission into the lasing mode, is varied. Typical values considered for  are 0.01ϽϽ1.0. We find that for large enough , lasing action, with properties similar to those predicted by semiclassical theories that factorize atom-field correlations and use a small-noise approximation, can occur. Squeezing can occur as  is increased. There is no evidence of a sharp phase transition from weakly excited thermal light to coherent light at a particular pump power. This is consistent with work on many-atom lasers with  values in the range considered here. As  is increased, the output goes from quasithermal light to coherent and finally to squeezed light, progressing into a fully quantum-mechanical regime. We also consider the effects of cavity damping and spontaneous emission rates on these results. ͓S1050-2947͑99͒06510-5͔
We report values of R = sigma(e(+)e(-)-->hadrons)/sigma(e(+)e(-)-->mu(+)mu(-)) for 85 center-of-mass energies between 2 and 5 GeV measured with the upgraded Beijing Spectrometer at the Beijing Electron-Positron Collider.
Lattice NRQCD with leading finite lattice spacing errors removed is used to calculate decay constants of mesons made up of heavy quarks. Quenched simulations are done with a tadpole improved gauge action containing plaquette and six-link rectangular terms. The tadpole factor is estimated using the Landau link. For each of the three values of the coupling constant considered, quarkonia are calculated for five masses spanning the range from charmonium through bottomonium, and one set of quark masses is tuned to the B c . "Perturbative" and nonperturbative meson masses are compared. One-loop perturbative matching of lattice NRQCD with continuum QCD for the heavy-heavy vector and axial vector currents is performed. The data are consistent with af V ∝ √ M V a and f Bc = 420(13) MeV. PACS number(s): 12.38
Using a sample of 3.8 M (2S) events accumulated with the BES detector, the process (2S) → ϩ Ϫ J/ is studied. The angular distributions are compared with the general decay amplitude analysis of Cahn. We find that the dipion system requires some D wave amplitude, as well as S wave. On the other hand, the J/Ϫ(ϩ Ϫ) relative angular momentum is consistent with being pure S wave. The decay distributions have been fit to heavy quarkonium models, including the Novikov-Shifman model. This model, which is written in terms of the parameter , predicts that D wave pions should be present. We determine ϭ0.183 Ϯ0.002Ϯ0.003 based on the joint m Ϫcos * distribution. The fraction of D wave amplitude as a function of m is found to decrease with increasing m , in agreement with the model. We have also fit the Mannel-Yan model, which is another model that allows D wave pions.
Addition of the organogermanium compound,
Me3GeS(CH2)3Si(OMe)3,
to a modified,
conventional sol−gel formulation gives a silica xerogel doped with
this molecular species.
Subsequent thermal treatment of this molecularly doped xerogel
under oxidizing then
reducing conditions affords nanoclusters of Ge highly dispersed
throughout the bulk of the
xerogel matrix. Under appropriate conditions, Ge nanoclusters
having an average diameter
of ca. 68 Å can be formed by this procedure. Characterization of
this nanocomposite material
by TEM, HRTEM, EDS, XRD, micro-Raman spectroscopy, electron
diffraction, and UV−visible spectroscopy indicates that the Ge nanoclusters are highly
crystalline and exhibit
optical properties consistent with those expected when quantum
confinement effects are
operative.
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