We studied the electroproduction of the Delta(1232) resonance via the reaction p(e,e'p)\pi0 at four-momentum transfers Qsq = 2.8 and 4.0 GeV^2. This is the highest Qsq for which exclusive resonance electroproduction has ever been observed. Decay angular distributions for Delta to p-pi0$ were measured over a wide range of barycentric energies covering the resonance. The $N-\Delta$ transition form factor G*_M and ratios of resonant multipoles E{1+}/M{1+} and S{1+}/M{1+} were extracted from the decay angular distributions. These ratios remain small, indicating that perturbative QCD is not applicable for this reaction at these momentum transfers.
CONST(NAME=E1+/M1+) and CONST(NAME=S1+/M1+) are the ratios of the electric quadrupole moment to magnetic dipole moment and Coulomb quadrupole moment to magnetic dipole moment, respectively (see paper). Resonance only.
CONST(NAME=E1+/M1+) and CONST(NAME=S1+/M1+) are the ratios of the electric quadrupole moment to magnetic dipole moment and Coulomb quadrupole moment to magnetic dipole moment, respectively (see paper). Resonance only.
CONST(NAME=E1+/M1+) and CONST(NAME=S1+/M1+) are the ratios of the electric quadrupole moment to magnetic dipole moment and Coulomb quadrupole moment to ma gnetic dipole moment, respectively (see paper). Resonance + background.
In the process e+e- to hadrons, one of the effects of gluon emission is to modify the 1+cos(theta)**2 form of the angular distribution of the thrust axis, an effect which may be quantified by the longitudinal cross-section. Using the OPAL detector at LEP, we have determined the longitudinal to total cross-section ratio to be 0.0127+-0.0016+-0.0013 at the parton level, in good agreement with the expectation of QCD computed to Order(alpha_s**2) Comparisions at the hadron level with Monte Carlo models are presented. The dependence of the longitudinal cross-section on the value of thrust has also been studied, and provides a new test of QCD.
Values of SIG(C=L) integrated over all Thrust.
Measured values of the differential cross section, and the corresponding ratio of longitudinal to total cross sections, corrected to the hadron level.
We report measurements of D ∗± production in interactions between 350 GeV/ c π − particles and nuclei. Reconstruction of the decay D ∗+ → D 0 π + and charge conugate, with D 0 identified via its decays to K − π + and K − π − π + π + , has allowed isolation of a sample of 611 ± 28 D ∗± mesons, produced at positive x F . Assuming a linear A-dependence, the cross-section per nucleon in the region x F > 0 is measured to be 1.41 ± 0.10 ± 0.11 μ b for D ∗+ and 1.84 ± 0.12 ± 0.15 μ b for D ∗− . We present measurements of differential cross-sections with respect to x F and P t 2 , and compare data for D ∗± (vector-meson) production with data for production of charmed pseudoscalar mesons.
No description provided.
Data on D0, DBAR0, D+, and D- meson production are taken from previous publication of this collaboration (see NP B495, 3).
No description provided.
The predicted effects of final state interactions such as colour reconnection are investigated by measuring properties of hadronic decays of W bosons, recorded at a centre-of-mass energy of sqrt(s)=182.7 GeV in the OPAL detector at LEP. Dependence on the modelling of hadronic W decays is avoided by comparing W+W- -> qqqq events with the non-leptonic component of W+W- -> qqlnu events. The scaled momentum distribution, its mean value, x_p, and that of the charged particle multiplicity, n_ch, are measured and found to be consistent in the two channels. The measured differences are: Diff(x_p) = +0.7 +- 0.8 +- 0.6 and Diff(n_ch) = (-0.09 +- 0.09 +-0.05)*10**-2. In addition, measurements of rapidity and thrust are performed for W+W- -> qqqq events. The data are described well by standard QCD models and disfavour one model of colour reconnection within the ARIADNE program. The current implementation of the ELLIS-GEIGER model of colour reconnection is excluded. At the current level of statistical precision no evidence for colour reconnection effects was found in the observables studied. The predicted effect of colour reconnection on OPAL measurements of M_W is also quantified in the context of models studied.
Here Z is defined as Z = 2*P(C=HADRON)/SQRT(S).
Absolute J/ ψ and ψ ′ production cross sections have been measured at the CERN SPS, with 450 GeV/ c protons incident on a set of C, Al, Cu and W targets. Complementing these values with the results obtained by experiment NA51, which used the same beam and detector with H and D targets, we establish a coherent picture of charmonia production in proton-induced reactions at SPS energies. In particular, we show that the scaling of the J/ ψ cross section with the mass number of the target, A, is well described as A α , with α ψ =0.919±0.015. The ratio between the J/ ψ and ψ ′ yields, in our kinematical window, is found to be independent of A, with α ψ ′ − α ψ =0.014±0.011.
The ratio of the production cross sections, in the di-muon channel. Note that there are wo set of CU and WT data with targets of different lengths. An average values is also given for these.
The J/PSI absolute cross sections, times the BR to di-muons.
The PSI(3685) absolute cross sections, times the BR to di-muons.
We report the first precision measurements of the scaled momentum, the charge multiplicity, and the thrust of hadronic jets in the Breit frame in Deep Inelastic Scattering ν μ N and ν ̄ μ N charged current events over the Q 2 range from 1 to 100 GeV 2 . The neutrino data, obtained in the NOMAD experiment at the CERN SPS, extend the Q 2 -evolution of these parameters by two orders of magnitude, and with commensurate precision, when compared to those reported by the ep and e + e − experiments.
Average neutrino energy. Peak postion of distribution on log(1/z) is presented.
Photonic events with large missing energy have been observed in $e^+ e^-$ collisions at centre-of-mass energies of 130, 136 and 183 GeV collected in 1997 using the OPAL detector at LEP. Results are presented for event topologies with a single photon and missing transverse energy or with an acoplanar photon pair. Cross-section measurements are performed within the kinematic acceptance of each selection. These results are compared with the expectations from the Standard Model process $e^+e^-$ $\rightarrow \nu \bar{\nu +}$ photon(s). No evidence is observed for new physics contributions to these final states. Using the data at $\sqrt{s} = 183$ GeV, upper limits on $\sigma$ ($e^+ e^-$ $\rightarrow$ X.Y)*BR(X $\to \textrm{Y}_{\gamma}$) and $\sigma$ ($e^+ e^-$ $\rightarrow$ X.X)*BR$^2$ (X $\to \textrm{Y}_{\gamma}$) are derived for the case of stable and invisible Y. These limits apply to single and pair production of excited neutrinos $(\textrm{X} = \nu^*, \textrm{Y} = \nu)$, to neutralino production $(\textrm{X} = \overline{\chi}^0_2, \textrm{Y} = \overline{\chi}^0_1)$ and to supersymmetric models in which $X = \overline{\chi}^0_1$ and $Y=\overline{\textrm{G}}$ is a light gravitino.
No description provided.
No description provided.
The data for sqrt(s) = 130 and 136 GeV are combination of present data and previous one (see EPJ C2, 607), the data for sqrt(s)=161 and 172 GeV is from thesame publication.
The structure of both quasi-real and highly virtual photons is investigated using the reaction e+e- -> e+e-mu+mu-, proceeding via the exchange of two photons. The results are based on the complete OPAL dataset taken at e+e- centre-of-mass energies close to the mass of the Z boson. The QED structure function F_2^gamma and the differential cross-section dsigdx for quasi-real photons are obtained as functions of the fractional momentum x from the muon momentum which is carried by the struck muon in the quasi-real photon for values of Q**2 ranging from 1.5 to 400 GeV**2. The differential cross-section dsigdx for highly virtual photons is measured for 1.5< Q**2 < 30 GeV**2 and 1.5< P**2 < 20 GeV**2, where Q**2 and P**2 are the negative values of the four-momentum squared of the two photons such that Q**2 > P**2. Based on azimuthal correlations the QED structure functions F_A^gamma and F_B^gamma for quasi-real photons are determined for an average Q**2 of 5.4 GeV**2.
No description provided.
No description provided.
No description provided.
Results are presented on dimuon production for invariant masses ranging from the dimuon threshold up to the $J/\Psi$ meson. Proton-tungsten and sulphur-tungsten int
No description provided.
No description provided.
No description provided.
DO has measured the inclusive production cross section of W and Z bosons in a sample of 13 pb$^{-1}$ of data collected at the Fermilab Tevatron. The cross sections, multiplied by their leptonic branching fractions, for production in pbar-p collisions at sqrt{s}=1.8 TeV are sigma_W*B(W->e nu) = 2.36+-0.02+-0.08+-0.13 nb, sigma_W*B(W->mu nu) = 2.09+-0.06+-0.22+-0.11 nb, sigma_Z*B(Z->e+ e-) = 0.218+-0.008+-0.008+-0.012 nb, and sigma_Z*B(Z->mu+ mu-) = 0.178+-0.022+-0.021+-0.009 nb, where the first uncertainty is statistical and the second systematic; the third reflects the uncertainty in the integrated luminosity. For the combined electron and muon analyses, we find sigma_W*B(W->l mu)/sigma_Z*B(Z->l+ l-) = 10.90+-0.52. Assuming standard model couplings, we use this result to determine the width of the W boson, and obtain Gamma(W) = 2.044+-0.097 GeV.
No description provided.
Combined electron and muon analysis.
Forum