The interaction of virtual photons is investigated using the reaction e+e- -> e+e- hadrons based on data taken by the OPAL experiment at e+e- centre-of-mass energies sqrt(s_ee)=189-209 GeV, for W>5 GeV and at an average Q^2 of 17.9 GeV^2. The measured cross-sections are compared to predictions of the Quark Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET to the NLO prediction for the reaction e+e- -> e+e-qqbar, and to BFKL calculations. PHOJET, NLO e+e- -> e+e-qqbar, and QPM describe the data reasonably well, whereas the cross-section predicted by a Leading Order BFKL calculation is too large.
Total cross section in the given phase space and assuming ALPHA = 1/137.
Differential cross section as a function of X where X is the maximum value of X1 or X2, the upper and lower vertex values.
Differential cross section as a function of Q**2 where Q**2 is the maximum value of Q1**2 or Q2**2, the upper and lower vertex values.
We report measurements of the asymmetry A_parallel for inclusive hadron production on longitudinally polarized proton and deuteron targets by circularly polarized photons. The photons were produced via internal and external bremsstrahlung from an electron beam of 48.35 GeV. Asymmetries for both positive and negative signed hadrons, and a subset of identified pions, were measured in the momentum range 10<P<30 GeV at 2.75 and 5.5 degrees. Small non-zero asymmetries are observed for the proton, while the deuteron results are consistent with zero. Recent calculations do not describe the data well.
The asymmetry for polarized photoproduction of inclusive hadrons from a polarized proton target. The errors are statistical only.
The asymmetry for polarized photoproduction of inclusive identified pions from a polarized proton target. The errors are statistical only.
The asymmetry for polarized photoproduction of inclusive hadrons from a polarized deuteron target. The errors are statistical only.
We examine the negative 3π final state produced in association with Δ++(1232) in the reaction γp→Δ++π+π−π− at an incident photon energy of 19.3 GeV. The most prominent enhancement in the 3π spectrum occurs at a mass and with a width consistent with the parameters of the a2(1320). This identification is confirmed by the various angular distributions. The a2 production cross section, corrected for efficiencies and alternate a2 decay modes, is 0.45±0.05 μb.
No description provided.
The reaction γγ → ϱ + ϱ − → π + π − π 0 π 0 has been studied with the ARGUS detector at the e + e − storage ring DORIS II at DESY. Near threshold, the cross section for this reaction is about four times smaller than for the reaction γγ → ϱ 0 ϱ 0 .
Data read from graph.
Data read from graph.
Data read from graph.
This paper reports studies of the reactions γp→ρ π π πp and γp→ρ ρ πp. In particular a peak is reported in the ρ ρ π mass spectrum with closely similar mass and width to those of the ω ρ π peak previously reported in the reaction γp→ω ρ πp. The ratio of production cross sections is found to be ρ ρ π/ω ρ π=0.96±0.19, in serious disagreement with the expectation from Vector Meson Dominance. A possible explanation is indicated.
No description provided.
Numerical values requested from authors.
Inclusive photoproduction of ϕ,K*0(890),\(\bar K*^0 \) andK*0(1420),\(\bar K*^0 \) has been studied in γp collisions with photons of energy 20 to 70 GeV and in the range 0.1≦xF≦0.95 [0.4≦xF≦0.8 for the\(\mathop K\limits^{( - )} *\)(1420)],xF being the Feynman variable of the vector/tensor meson. The cross-sections for these processes, averaged over the photon energy range and integrated overxF are given. The inclusive ϕ production in the forward direction can be described quantitatively by a triple-Regge model calculation. The remaining ϕ production and the totalK*0(890) and\(\bar K*^0 \) production are consistent with a quark fusion picture.
No description provided.
In diffractive photoproduction ofηπ+π−, the two-body substatesηρ0 andA2π are found to contribute significantly to the cross-section forηπ+π− masses below 2.4 GeV. From a spin-parity analysis the branching ratio, ρ′(1600)→ηρ/ρ′(1600)→, is determined to be <0.02 at the 68.3% confidence level. TheA2π component shows an enhancement around 1.7 GeV. The spin-parity analysis indicates a probable contribution to this signal from exclusive photoproduction of theg(1690).
No description provided.
Not corrected for 35% background under the eta --> gamma gamma peak.
Not corrected for 35% background under the ETA --> GAMMA GAMMA peak.
The photoproduction of the final state ω π+π−π0 has been studied as part of a survey of photoproduction in the energy range 20–70 GeV in the Omega spectrometer at CERN. The π+π−π0 system produced with the ω meson has a strongρ±π± component which is predominantlyI=1 andJπ=1+. For theωρ±π∓ state a spin-parity analysis favoursJπ=1−, and the mass spectrum peaks at 2.28±0.05 GeV. The fitted width is Γ=0.44±0.11 GeV. The photoproduction cross-section of theωρ±π∓ state, averaged over the energy range 25–60 GeV, is 150±50 nb.
Figure gives data in 7 momenta bins. Averaged result is given here.
Seventy-one events containing charmed-particle decays have been observed in an experiment using the SLAC Hybrid Facility exposed to a backward-scattered photon beam. Several improvements were made to the apparatus since the previous experiment on charm photoproduction. Results for the charmed-meson lifetimes are consistent with the published results from the previous experiment and the two data samples have been combined yielding a total sample of 136 charm events. After imposing rigorous cuts, 50 neutral, 48 charged, and 2 charged/neutral ambiguous decays remain. From these, the charmed-meson lifetimes are measured to be &=(8.6±1.3−0.3+0 .7)×10−13 sec, &=(6.1±0.9±0.3)×10 −13 sec, and their ratio &=1.4±0.3− 0.1+0.2. The total charm cross section at a photon energy of 20 GeV has been measured to be (62±8−10+15) nb. There is evidence for both DD¯X and D¯Λc+X production with σD¯Λc+X/σcharm=(71± 11±6)%.
No description provided.
Cross sections are presented for the inclusive photoproduction of KS0, Λ, Λ¯, Ξ−, Ξ¯−, Σ0, and Σ*±(1385) at 20 GeV. An upper limit to Ω− production is also given. The data come from 284 000 hadronic events photoproduced in the SLAC 1-m hydrogen-bubble-chamber hybrid facility exposed to a nearly monochromatic, polarized 20-GeV backscattered photon beam. A comparison of the KS0, Λ, Λ¯, and Ξ− rates per inelastic event to π±p data show that γp rates are consistent with being higher than the π±p rates, providing evidence of an ss¯ component of the photon. The pair cross sections for KS0KS0, KS0Λ, KSoΛ¯, and ΛΛ¯ are presented. The xF distributions of the Λ, Λ¯, and Ξ− are compared to a quark-diquark fusion model, giving information on strange-baryon photoproduction mechanisms.
No description provided.
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