The cross section for the fully constrained reaction ep→eppp¯ has been determined as a function of the electroproduction variables Q2 and s, in the range 0.7<Q2<3 GeV2 and 8<s<16 GeV2. Evidence is presented and cross-section estimates are made for resonances in the final-state p¯p system.
The cross section for virtual photon are derived from E- P cross section bydividing on the virtual-photon flux factor.
The cross section for virtual photon are derived from E- P cross section bydividing on the virtual-photon flux factor.
We report new measurements of the inclusive electroproduction of forward protons carried out at the Wilson Synchrotron Laboratory at Cornell University. Data were taken with deuterium at the (W, Q2) points (2.15 GeV, 1.2 GeV2), (2.15, 4.0), and (3.11, 1.2); data were taken with hydrogen at these points and at the points (2.15, 2.0), (2.67, 3.3), and (3.11, 1.7). The invariant structure function is presented in terms of W, Q2, and ω.
No description provided.
From 2540 Z 0 → τ + τ − events, we determine the inclusive decay branching fractions of the τ -lepton into one and three charged particles to be 0.856 ± 0.006 (stat.) ± 0.003 (syst.) and 0.144 ± 0.006 (stat.) ± 0.003 (syst.), respectively. The leptonic branching fractions are measured to be 0.175 ± 0.008 (stat.) ± 0.005 (syst.) for τ → μν μ ντ and 0.177 ± 0.007 (stat.) ± 0.006 (syst.) for τ → eν e ν τ . We determined the τ lifetime both from three-prong decays using the decay length and from one-prong decays using the impact parameter. The results from the two independent methods agree and yield a combined value of [0.309 ± 0.023 (stat.) ± 0.030 (syst.)] × 10 −12 s.
ALPHAS extracted from the ratio of the branching fractions.
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No description provided.
The ratio of the branching fractions for p p →K + K − and p p →π + π − was determined with the CPLEAR detector, by stopping antiprotons in a gaseous hydrogen target at 15 bar pressure. It was found to be BR(K + K − )/BR( π + π − )=0.205± 0.016. The fraction of P-wave annihilation at rest at this target density was deduced to be (38±9)%.
CONST is the fraction of P-wave annihilation in gaseous hydrogen at pressu re of 15 bar. In the SIG/SIG the statistical and systematic errors are added qu adratically.
Deep inelastic electron-photon scattering is studied in the Q2 ranges from 6 to 30 GeV2 and from 60 to 400 GeV2 using the full sample of LEP data taken with the OPAL detector at centre-of-mass energies close to the Z0 mass, with an integrated luminosity of 156.4 pb−1. Energy flow distributions and other properties of the measured hadronic final state are compared with the predictions of Monte Carlo models, including HERWIG and PYTHIA. Sizeable differences are found between the data and the models, especially at low values of the scaling variable x. New measurements are presented of the photon structure function $F_2^{αmma }(x,Q^2)$, allowing for the first time for uncertainties in the description of the final state by different Monte Carlo models. The differences between the data and the models contribute significantly to the systematic errors on $F_2^{αmma }$. The slope ${⤪ d}(F_2^{αmma }/←pha )/{⤪ d ln} Q^2$ is measured to be $0.13_{-0.04}^{+0.06}$.
No description provided.
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Using modularized NaI(Tl) detectors, we carried out a high statistics measurement of inclusive γ-ray, π0, and η spectra, and determined the branching ratios or upper limits of Pontecorvo reactions p¯d→π0n, π0Δ0, ηn, and ηΔ0 from the corresponding monochromatic peaks in them. The obtained branching ratios are B(p¯d→π0n)=(1.03±0.41)×10−5, B(p¯d→π0Δ0)=(4.67±1.66)×10−5, B(p¯d→ηn)<8.94×10−6 (95% C.L.), and B(p¯d→ηΔ0)<6.49×10−5 (95% C.L.).
No description provided.
We have measured the photon yield in lepton pair events recorded by the OPAL detector in a data sample corresponding to an integrated luminosity of 7.1 pb −1 at centre-of-mass energies between 88 GeV and 94 GeV. The results are compared to QED expectations for initial and final state photon radiation. No anomalous photon yield has been found, and stringent limits on the branching ratio for exotic radiative three body Z 0 decays into a photon and a pair of leptons are obtained. We also place limits on possible Z 0 decays into a photon and a resonance X with subsequent decays of X into a pair of leptons. Acollinear μ + μ − events with missing momentum along the beam direction are identified as events with hard initial state photon radiation and used to measure an average cross section of 15 ± 8 6 pb for e + e − annihilation into μ + μ − , in the so far untested range of centre-of-mass energies between 60 GeV and 84 GeV. This value is consistent with a cross section of 24 pb, expected from Z 0 and photon exchange.
No description provided.
The total cross section for hadron production by inelastic electron scattering at 3.2° from a number of nuclei has been measured at several virtual photon energies at fixed Q2=0.1 (GeV/c)2. The hadronic cross section is measured directly, by detecting at least one hadron in coincidence with the scattered electron. The results show very little shadowing and no detectable energy dependence. These observations contradict vector-meson dominance.
N(C=N) and N(C=P) are the numbers of the neutrons and protons in nucleus.
We present measurement of the π0γ*γ, ηγ*γ and η′γ*γ form factors. The π0-form factor is for the first time observed in the space-like region. The transition form factor of the η-meson is determined from its decay modes π+π−π0, π+π−γ and the neutral decay mode γγ. The decay of the η′ is observed in the decay channels ργ, ηπ+π− with η→γγ and in the four charged prong final state stemming from ηπ+π− with the η decaying into π+π−(π0/γ). All form factors agree well with a simple ρ-pole predicted by the vector meson dominance model and also with the QCD inspired Brodsky-Lepage model.
No description provided.
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