Nuclear Shadowing in DIS: Numerical Solution of the Evolution Equation for the Green Function

Within a light-cone QCD formalism based on the Green function technique incorporating color transparency and coherence length effects we study nuclear shadowing in deep-inelastic scattering at moderately small Bjorken x_{Bj}. Calculations performed so far were based only on approximations leading to an analytical harmonic oscillatory form of the Green function. We present for the first time an exact numerical solution of the evolution equation for the Green function using realistic form of the dipole cross section and nuclear density function. We compare numerical results for nuclear shadowing with previous predictions and discuss differences.Comment: 21 pages including 3 figures; a small revision of the tex

Structural thermal stability of graphene oxide-doped copper-cobalt oxide coatings as a solar selective surface

3d transition metal oxides based thin film coatings such as copper-cobalt oxides exhibit high absorption in the visible region and low emittance in the infra-red to far-infra-red region of the solar spectrum which is favourable for use as potential selective surface materials in photothermal devices. These materials have the potential to minimize heating while increasing absorption in the operative spectrum range and therefore achieve higher solar selectivity. A series of mixed copper-cobalt metal spinel oxides (CuxCoyOz) doped with graphene oxide thin films were deposited on commercial grade aluminium substrates using a sol–gel dip-coating technique at an annealing temperature of 500 °C in air for 1 h. Characterizations of the synthesized films were carried out by high temperature synchrotron radiation X-ray Diffraction (SR-XRD), UV-Vis, Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron microscopy (XPS) techniques. High thermal stability of coatings with multiple phases, binary and ternary metal oxides, was defined through SR-XRD study. FTIR analysis shows moderate (<80%) to high (up to 99%) reflectance in the infra-red region while the UV-Vis investigations demonstrate that, in the visible region, solar absorption increases gradually (up to 95%) with the addition of graphene oxide to the CuxCoyOz coatings. With the incorporation of 1.5 wt% of graphene oxide to the copper-cobalt oxide coatings, a high solar selectivity of 29.01 (the ratio of the average solar absorptance in visible and the average thermal emittance in infra-red to far infra-red region; α/ε) was achieved

Progress in the determination of the J/ψ−πJ/\psi-\pi cross section

Improving previous calculations, we compute the $J/\psi \pi\to {charmed mesons}$ cross section using QCD sum rules. Our sum rules for the $J/\psi \pi\to \bar{D} D^*$, $D \bar{D}^*$, ${\bar D}^* D^*$ and ${\bar D} D$ hadronic matrix elements are constructed by using vaccum-pion correlation functions, and we work up to twist-4 in the soft-pion limit. Our results suggest that, using meson exchange models is perfectly acceptable, provided that they include form factors and that they respect chiral symmetry. After doing a thermal average we get $\sim 0.3$ mb at T=150\MeV.Comment: 22 pages, RevTeX4 including 7 figures in ps file

Bose-Einstein Correlations of Neutral and Charged Pions in Hadronic Z Decays

Bose-Einstein correlations of both neutral and like-sign charged pion pairs are measured in a sample of 2 million hadronic Z decays collected with the L3 detector at LEP. The analysis is performed in the four-momentum difference range 300 MeV < Q < 2 GeV. The radius of the neutral pion source is found to be smaller than that of charged pions. This result is in qualitative agreement with the string fragmentation model

Measurement of the W+W-gamma Cross Section and Direct Limits on Anomalous Quartic Gauge Boson Couplings at LEP

The process e+e- -> W+W-gamma is analysed using the data collected with the L3 detector at LEP at a centre-of-mass energy of 188.6GeV, corresponding to an integrated luminosity of 176.8pb^-1. Based on a sample of 42 selected W+W- candidates containing an isolated hard photon, the W+W-gamma cross section, defined within phase-space cuts, is measured to be: sigma_WWgamma = 290 +/- 80 +/- 16 fb, consistent with the Standard Model expectation. Including the process e+e- -> nu nu gamma gamma, limits are derived on anomalous contributions to the Standard Model quartic vertices W+W- gamma gamma and W+W-Z gamma at 95% CL: -0.043 GeV^-2 < a_0/Lambda^2 < 0.043 GeV^-2 0.08 GeV^-2 < a_c/Lambda^2 < 0.13 GeV^-2 0.41 GeV^-2 < a_n/Lambda^2 < 0.37 GeV^-2

Production of Single W Bosons at \sqrt{s}=189 GeV and Measurement of WWgamma Gauge Couplings

Single W boson production in electron-positron collisions is studied with the L3 detector at LEP. The data sample collected at a centre-of-mass energy of \sqrt{s} = 188.7GeV corresponds to an integrated luminosity of 176.4pb^-1. Events with a single energetic lepton or two acoplanar hadronic jets are selected. Within phase-space cuts, the total cross-section is measured to be 0.53 +/- 0.12 +/- 0.03 pb, consistent with the Standard Model expectation. Including our single W boson results obtained at lower \sqrt{s}, the WWgamma gauge couplings kappa_gamma and lambda_gamma are determined to be kappa_gamma = 0.93 +/- 0.16 +/- 0.09 and lambda_gamma = -0.31 +0.68 -0.19 +/- 0.13

Search for Neutral Higgs Bosons of the Minimal Supersymmetric Standard Model in e+e- Interactions at \sqrt{s} = 189 GeV

A search for the lightest neutral scalar and neutral pseudoscalar Higgs bosons in the Minimal Supersymmetric Standard Model is performed using 176.4 pb^-1 of integrated luminosity collected by L3 at a center-of-mass energy of 189 GeV. No signal is observed, and the data are consistent with the expected Standard Model background. Lower limits on the masses of the lightest neutral scalar and pseudoscalar Higgs bosons are given as a function of tan(beta). Lower mass limits for tan(beta)>1 are set at the 95% confidence level to be m_h > 77.1 GeV and m_A > 77.1 GeV

Measurement of Bose-Einstein Correlations in e+e- -> W+W- at root(s)=189GeV

We investigate Bose-Einstein correlations (BEC) in W-pair production at root(s)=189GeV using the L3 detector at LEP. We observe BEC between particles from a single W decay in good agreement with those from a light-quark Z decay sample. We investigate their possible existence between particles coming from different W's. No evidence for such inter-W BEC is found

Search for an invisibly decaying Higgs boson in e^+e^- collisions at \sqrt{s} = 183 - 189 GeV

A search for a Higgs boson decaying into invisible particles is performed using the data collected at LEP by the L3 experiment at centre-of-mass energies of 183 GeV and 189 GeV. The integrated luminosities are respectively 55.3 pb^-1 and 176.4 pb^-1. The observed candidates are consistent with the expectations from Standard Model processes. In the hypothesis that the production cross section of this Higgs boson equals the Standard Model one and the branching ratio into invisible particles is 100%, a lower mass limit of 89.2 GeV is set at 95% confidence level

Search for Heavy Neutral and Charged Leptons in e+ e- Annihilation at LEP

A search for exotic unstable neutral and charged heavy leptons as well as for stable charged heavy leptons is performed with the L3 detector at LEP. Sequential, vector and mirror natures of heavy leptons are considered. No evidence for their existence is found and lower limits on their masses are set