Two-photon production of the hadronic final states K + K − π + π − and K + K − π + π 0 π − has been studied using the ARGUS detector at the e + e − storage ring DORIS II at DESY. The cross sections of the reactions γγ → øϱ 0 and γγ → øω have been measured for the first time. In addition, angular distrubutions have been determined for the reaction γγ → øϱ 0 → K + K − π + π − .
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A measurement of the cross section for the combined two-photon production of charged pion and kaon pairs is performed using 1.2~$\rm fb^{-1}$ of data collected by the CLEO~II detector at the Cornell Electron Storage Ring. The cross section is measured at invariant masses of the two-photon system between 1.5 and 5.0 GeV/$c^2$, and at scattering angles more than $53^\circ$ away from the $\gamma\gamma$ collision axis in the $\gamma\gamma$ center-of-mass frame. The large background of leptonic events is suppressed by utilizing the CsI calorimeter in conjunction with the muon chamber system. The reported cross section is compared with leading order QCD models as well as previous experiments. In particular, although the functional dependence of the measured cross section disagrees with leading order QCD at small values of the two-photon invariant mass, the data show a transition to perturbative behavior at an invariant mass of approximately 2.5 GeV/$c^2$. hardcopies with figures can be obtained by writing to to: Pam Morehouse preprint secretary Newman Lab Cornell University Ithaca, NY 14853 or by sending mail to: preprints@lns62.lns.cornell.edu
There is an additional 10 pct point-to-point systematic error as well as the overall uncertainty given above.
The total and the differential cross sections for the reaction e + e − → γγ ( γ ) have been measured with the DELPHI detector at LEP using an integrated luminosity of 36.9 pb −1 . The results agree with the QED predictions and consequently there is no evidence for non-standard channels with the same experimental signature. The lower limits obtained on the QED cutoff parameters are Λ + > 143 GeV and Λ − > 120 GeV, and the lower bound on the mass of an excited electron with an effective coupling constant λ γ = 1 is 132 GeV/ c 2 . Upper limits on the branching ratios for the decays Z 0 → γγ , Z 0 → π 0 γ , Z 0 → ηγ and Z 0 → γγγ have been determined to be 5.5 × 10 −5 , 5.5 × 10 −5 , 8.0 × 10 −5 , and 1.7 × 10 −5 respectively. All the limits are at the 95% confidence level.
1990 energies are 88.223, 89.222, 90.217, 91.217, 92.209, 93.208 and 94.202 GeV.. 1991 energies are 88.465, 89.460, 90.208, 91.225, 91.954, 92.953, and 93.703 GeV.. 1992 energy is 91.278 GeV.
Average of all data.
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During the 1992 running period of the LEP e + e − collider, the DELPHI experiment accumulated approximately 24 pb − of data at the Z 0 peak. The decays into hadrons and charged leptons have been analysed to give values for the cross sections and leptonic forward-backward asymmetries which are significantly improved with respect to those previously published by the DELPHI collaboration. Incorporating these new data, more precise values for the Z 0 resonance parameters are obtained from model-independent fits. The results are interpreted within the framework of the Standard Model, yielding for the top quark mass m t = 157 −48 +36 (expt.) −20 +19 (Higgs) GeV, and for the effective mixing angle sin 2 θ eff lept = 0.2328 ± 0.0013 (expt.) −0.0003 +0.0001 (Higgs), where (Higgs) represents the variation due to Higgs boson mass in the range 60 to 1000 GeV, with central value 300 GeV.
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First result corresponds to the total cross section (i.e. S+T channel), while second one corresponds to S-channel only. An acollinearity less that 10 deg.
Forward-backward asymmetry within the polar angular range 44 < THETA < 136 degrees and acollinearity < 10 degrees.. First result corresponds to the total cross section (i.e. S+T channel), while second one corresponds to S-channel only.
We present a measurement of the ratio σB(W→eν)σB(Z0→e+e−) in p¯p collisions at s=1.8 TeV The data represent an integrated luminosity of 21.7 pb−1 from the 1992-1993 run of the Collider Detector at Fermilab. We find σB(W→eν)σB(Z0→e+e−)=10.90±0.32(stat)±0.29(syst). From this value, we extract a value for the W width, Γ(W)=2.064±0.061(stat)±0.059(syst) GeV, and the branching ratio, Γ(W→eν)Γ(W)=0.1094±0.0033(stat)±0.0031(syst), and we set a decay-mode-independent limit on the top quark mass mtop>62 GeV/c2 at the 95% C.L.
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The s dependence of the electromagnetic proton form factors in the time-like region has been determined from the threshold ( s = 4 M p 2 ) up to s = 4.2 GeV 2 . Data were collected in a dedicated experiment performed at the LEAR antiproton ring at CERN, increasing by one order of magnitude the available statistics. Total and differential cross section of the p p → e − e + reaction have been measured. The electric and magnetic form factors are found to have comparable value. The observed form factor shows a clear steep s dependence close to the threshold.
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The φπ + /ωπ + ratio from n¯p annihilations on a liquid hydrogen target, for n¯ momenta between 64 and 297 MeV/ c , was measured using the OBELIX spectrometer at LEAR. The ratio R(ϕπ/ωπ)=σ(n¯p→ϕπ+)/σ(n¯p→ωπ+) turned out 0.110±0.015 stat ±0.006 syst . Implications of this result on the OZI rule are discussed.
Assumes branching ratios of (49.1 +- 0.8)% for phi --> K+ K- and (88.8 +- 0.6)% for omega --> pi+ pi- pi0.
The total cross section of the pp→ pp η reaction has been measured at incident proton energies of 1.265, 1.3, 1.4 and 1.5 GeV by detecting the two photons from the η decay in the PINOT spectrometer. The data are compared with other near-threshold measurements and with the predictions of existing theoretical calculations.
Value given at 1263 MeV assumes energy 2 MeV lower than nominal value. This uncertainty only affects this lowest energy point.
A liquid hydrogen target was used to study the nuclear fragmentation of beams of relativistic heavy ions, Ne22 to Ni58, over an energy range 400 to 900 MeV/nucleon. The experiments were carried out at the Lawrence Berkeley Laboratory Bevalac HISS facility, using the charge-velocity-rigidity method to identify the charged fragments. Here we describe the general concept of the experiment and present total charge-changing cross sections obtained from 17 separate runs. These new measured cross sections display an energy dependence which follows semiempirical model predictions. The mass dependence of the cross sections behaves as predicted by optical models, but within the experimental energy range, the optical model parameters display a clear energy dependence. The isospin of the projectile nuclei also appears to be an important factor in the interaction process.
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Annihilation cross-sections σann for antineutrons on some nuclei (C, Al, Cu, Sn and Pb) at three antineutron momenta (180, 240 and 280 MeV/c) were measured at LEAR (CERN) with the OBELIX spectrometer. A behaviour σann=σ0Aν has been found withν≈2/3. The data are discussed following some models for antineutron-nucleus interaction.
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