We have searched for a neutral $H$ dibaryon decaying via $H\rightarrow\Lambda n$ and $H\rightarrow\Sigma~0 n$. Our search has yielded two candidate events from which we set an upper limit on the $H$ production cross section. Normalizing to the inclusive $\Lambda$ production cross section, we find $(d\sigma_H/d\Omega)\,/\,(d\sigma_\Lambda/d\Omega) < 6.3\times 10~{-6}$ at 90\% C.L., for an $H$ of mass $\approx$\,2.15GeV/$c~2$.
No description provided.
The reactions γp→K+ Λ and γp→K+ Σ0 have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the Λ polarization and, for the first time, the Σ0 polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both Λ and Σ0 is substantial at all energies and varies strongly with the production angle.
Differential cross sections.
Total cross sections.
Differential cross sections.
The differential cross sections for antiproton elastic scattering on 4 He at 192.8 MeV/ c are measured. The annihilation cross section σ a = (377.6 ± 8.0) mb, the elastic cross section σ el = (206.3 ± 6.6) mb and the total p 4 He interaction cross section σ tot = (583.9 ± 10.4) mb are determined. The ratio of the real to imaginary part of the forward p 4 He amplitude is found: π =−0.17± 0.33 0.24 . Partial wave analysis reveals that the S, P and D waves are essential in this energy region.
Charged prong multiplicity distributions in pbar HE annihilation.
Mean charged particle multiplicity in pbar HE4 annihilations.
No description provided.
The reaction e + e − → τ + τ − has been studied at centre of mass energies between 14.0 and 46.8 GeV with the CELLO detector at the PETRA e + e − collider. We present results for the cross section σ τ and the charge asymmetry A τ . The results are in good agreement with the standard model. We have also measured the topological decay rates BR 1 , BR 3 and BR 5 for the inclusive decay of the τ lepton into one, three and five charge particles. The results confirm and improve earlier CELLO measurements at other energies. We find for the combined values at all energies BR 1 = (84.9 ± 0.4 ± 0.3)%, BR 3 = (15.0 ± 0.4 ± 0.3)% and BR 5 = (0.16 ± 0.13 ± 0.04)%.
No description provided.
No description provided.
Corrected for radiative effects and background contributions.
The e + e − → μ + μ − reaction has been studied at centre of mass energies ranging between 38.3 abd 46.8 GeV with the CELLO detector at PETRA. We present results on the cross section and the charge asymmetry for this channel. Combining all the data at the average energy 〈 s 〉=43 GeV we obtain R μμ =〈 σ μμ / σ 0 〉=0.98±0.04±0.04, 〈 A μμ 〉=(−14.1±3.7±1.0)%, where σ 0 is the QED cross section and A μμ is the charge asymmetry corrected for pure radiative effects. These results are in good agreement with the expected values of R μμ =1.01 and A μμ =−14.5% at that energy.
Mu-pair cross sections.
Corrected angular distributions with data sample divided into two energy regions with means 39 and 44 GeV and total energy region.
Forward-backward asymmetry.
We have studied 419 τ pair events produced in the reactione+e−→τ+ τ− at a c.m. energy of 34.6 GeV. We measure the cross section and angular distribution, as well as the decay branching ratios. The production characteristics are consistent with the Standard Electroweak Model predictions of γ andZ0 interference. The branching ratios are generally consistent with the τ decaying according to standard weak interaction principles, but we observe somewhat more decays resulting in single charged hadrons plus neutrals than are predicted by present theory.
Corrected for radiative effects.
Measured cross section relative to Standard Model Prediction.
Asymmetry based on fits to angular distribution.
The differential cross section of the reactione+e−→e+e− at a c.m. energy of 34.7 GeV has been measured. The result, together with our previously measurede+e−→α+α− data, are compared with the standard model predictions. We obtain for the weak neutral current couplings the valuesgv2=0.09×0.06,ga2=0.38×0.08. A fit of the Weinberg mixing angle gives the valuegv2=0.09×0.06,ga2=0.038×0.08. The data are also used to set limits on possible deviations from the pointlike structure of leptons. An upper limit for thee+e− coupling to a heavy spin 0 boson is also given.
Fully corrected results for Bhabha scattering.
The differential cross section for Bhabha scattering.
??? CONSTANTS ???.
We have studied the reactions e + e − → e + e − , e + e − → γγ , e + e − → μ + μ − , and e + e − → τ + τ − in the centre-of-mass (CM) energy range from 39.8 to 45.2 GeV using the CELLO detector at PETRA. Upper limits on the partial widths for new spin 0 bosons with masses both within and above the energy range covered are determined. No evidence for contributions of such new particles has been observed up to the highest PETRA energies in a model independent way. Under the assumptions of recently suggested models relating the existence of spin 0 bosons to the radiative width Γ τ of the Z 0 we exclude such bosons at the 95% confidence level for masses below the Z 0 -mass if Γ τ > 20 MeV.
No description provided.
Figure actually gives the 95 PCT CL upper limits of the coupling constants for each process as a function of the mass of the intermediate spin zero boson.
We report measurements of the electroproduction of single charged pions from hydrogen and deuterium targets for values of ε in the range 0.35<ε<0.45. Data were taken with a hydrogen target at the (W, Q2) points (2.15 GeV, 1.2 GeV2), (2.65, 2.0), (2.65, 3.4), (2.65, 6.0), and (2.65, 10.0). Data were taken with a deuterium target at the (W, Q2) points (2.15, 1.2) and (2.65, 2.0). The transverse cross section obtained by using these data in conjunction with earlier data at high ε to separate the longitudinal and transverse components is used in conjunction with the new data and the t-channel Born term to determine the pion form factor and to re-evaluate previously reported measurements. In the range 0.15 GeV2<Q2<10.0 GeV2 the pion form factor can be described by the simple pole form [1+Q2(0.462±0.024)]−1.
SEPARATED TRANSVERSE AND LONGITUDINAL VIRTUAL-PHOTON CROSS SECTIONS PREVIOUSLY PUBLISHED IN C. J. BEBEK ET AL., PRL 37, 1326 (1976).
DATA POINT 1 (HYDROGEN TARGET).
DATA POINT 1 (HYDROGEN TARGET).
We present evidence for a large scalar contribution to the cross section for the reaction ep→eK+Λ. No evidence for a scalar contribution is found for the reaction ep→eK+Σ0. This is reminiscent of the results for the π+n and π+Δ0 final states.
AVERAGED OVER PHI. FOR LOW EPSILON, SOME DEUTERIUM DATA ARE INCLUDED. INCLUDING EARLIER MEASUREMENTS AT HIGH EPSILON.
AVERAGED OVER PHI. INCLUDING EARLIER MEASUREMENTS AT HIGHER EPSILON.
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