We report measurements of the two-photon processes e+e−→e+e−π+π− and e+e−→e+e−K+K−, at an e+e− center-of-mass energy of 29 GeV. In the π+π− data a high-statistics analysis of the f(1270) results in a γγ width Γ(γγ→f)=3.2±0.4 keV. The π+π− continuum below the f mass is well described by a QED Born approximation, whereas above the f mass it is consistent with a QCD-model calculation if a large contribution from the f is assumed. For the K+K− data we find agreement of the high-mass continuum with the QCD prediction; limits on f′(1520) and θ(1720) formation are presented.
Data read from graph. Additional overall systematic error 20% not included.
Data read from graph.. Additional overall systematic error 20% not included.
Data read from graph.. Additional overall systematic error 20% not included.. The Q**2 dependence is normalized to unity for the bin centred on Q**2 = 0.
We have measured the processe+e−→e+e−+hadrons, where one of the scattered electrons was detected at large angles, withQ2 ranging from 7 to 70 (VeV/c)2. The photon structure functionF2γ(x, Q2) was determined at an averageQ2 of 23 (GeV/c)2. The measurements were compared to theoretical predictions of the Quark Parton Model and Quantum Chromodynamics. In both models a hadronic part was added. Within the errors the data are in agreement with the QPM using quark masses of 300 MeV/c2 for the light quarks. The data also agree with a QCD calculation including higher order corrections. A fit yielded a\(\Lambda _{\overline {MS} } \) value of 140−65+190 MeV, where the errors include statistical and systematic uncertainties.
No description provided.
BEBC filled in turn with hydrogen, and with a neon-hydrogen mixture, was exposed to the CERN SPS wide band neutrino and antineutrino beams. The ratios of the charged-current cross sections per nucleon, σ(νH 2 ) σ(ν Ne ) and σ( ν H 2 ) σ( ν Ne ) , between 20 and 300 GeV were found to be 0.656 ± 0.020 and 1.425 ± 0.052, respectively. Multiplying these ratios by the revised cross sections in neon, σ(ν Ne ) E = (0.723 ± 0.038) × 10 −38 cm 2 / GeV per nucleon and σ( ν Ne ) E = (0.351 ± 0.019) × 10 −38 cm 2 / GeV per nucleon, and their ratio, σ( ν Ne ) σ(ν Ne ) = 0.485 ± 0.020 ,, yields values for the total charged-current cross sections on protons, σ(νp)/ E and σ( ν p ) E , of (0.474 ± 0.029) × 10 −38 cm 2 /GeV and (0.500 ± 0.032) × 10 −38 cm 2 /GeV. respectively, and a value for the ratio σ( ν p ) σ(ν p ) of 1.053 ± 0.066.
No description provided.
The multiplicities per event of π ± and K ± are measured separately for e + e - annihilation into c c , b b , and light quark pairs at E cm=29 GeV. The K ± multiplicity is higher for heavy quark events than for light quark events. The π ± multiplicity and the π ± scaled differential cross section at low x = E beam/ E beam are found to be higher for b b events than for other events.
Numerical values requested from authors. Data given separately for (b bbar), (c cbar) and light quark jets.
Measured multiplicities for (b bbar) jets.
Measured multiplicities for (c cbar) jets.
We report on the first search with virtual photon-photon collisions for narrow, neutral resonances with even C parity in the mass range 4.5<W<19 GeV. The data were obtained via the process e+e−→e+e−γ*γ*→e e−+R with both the scattered e+ and e− detected. We find upper limits (95% confidence level) for the partial decay width of a resonance into two photons, ranging from 50 keV at W=4.5 GeV to 10 MeV at W=19 GeV. These limits constrain theoretical models involving neutral composite bosons.
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.
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.
The two-photon production of the η meson has been observed, and a value has been determined for the two-photon η decay width by a measurement of the cross section σ(e+e−→e+e−η) where η→γγ. The measurement was made with the TPC/Two-Gamma facility at the SLAC e+e− collider PEP, with an accumulated data sample of 64.5 pb−1. The η→γγ events were both triggered and detected by the pole-tip calorimeter. The measured two-photon η decay width is Γη→γγ=0.64±0.14 (statistical) ±0.13 (systematic) keV, in agreement with earlier similarly determined values.
No description provided.
The production of charmed D* mesons in e+e− annihilations at a center-of-mass energy of 29 GeV has been studied using the time-projection-chamber (TPC) detector at the SLAC storage ring PEP. The production cross section, fragmentation function, and forward-backward asymmetry due to electroweak effects are measured, and a limit on D0-D¯0 mixing is determined.
No description provided.
No description provided.
An analysis of the production ofKS0KS0 andK±Ks0π∓ by two quasi-real photons is presented. The cross section forγγ→K0\(\overline {K^0 } \), which is given for the γγ invariant mass range fromK\(\bar K\) threshold to 2.5 GeV, is dominated by thef′(1525) resonance and an enhancement near theK\(\bar K\) threshold. Upper limits on the product of the two-photon width times the branching ratio intoK\(\bar K\) pairs are given forΘ(1700),h(2030), and ξ(2220). For exclusive two-photon production ofK±Ks0π∓ no significant signal was observed. Upper limits are given on the cross section ofγγ→K+\(\overline {K^0 } \)π− orK−K0π+ between 1.4 and 3.2 GeV and on the product of the γγ width times the branching ratio into theK\(\bar K\)π final states for theηc(2980) and the ι(1440), yieldingΓ(γγ)→i(1440))·BR(i(1440)→K\(\bar K\)π<2.2 keV at 95% C.L.
Data read from graph.. Corrected for the angular distribution, which is assumed to be sin(theta)**4 for W > 1.14 GeV and isotropic in the first bin.
Data read from graph.
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