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)%.
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Corrected for radiative effects and background contributions.
The reactione+e−→µ+µ− has been studied at centre of mass energies between 35.0 and 46.8 GeV using the TASSO detector at PETRA. We present measurements of the forward-backward charge asymmetry (Aμμ) and cross section σμμ for this reaction at three energies. At 35.0 GeV we obtain a cross section relative to the QED prediction ofRμμ=σμμ/σo=0.932±0.018±0.044 andAμμ=(−10.6−2.3+2.2±0.5)%. At 38.3 GeV we findRμμ=0.951±0.072−0.057+0.063 andAμμ=(+1.7−8.6+8.5±0.5)%. At 43.6 GeV we measureRμμ=0.921±0.037±0.055 andAμμ=(−17.6−4.3+4.4±0.5)%. Our results are in good agreement with the predictions of the standard model. Including previous TASSO data we present improved determinations of muonic electroweak parameters. We also report on lower limits of possible contributions from contact interactions.
If only one error is given, this is the sum of the statistical and systematic errors in quadrature.
The data are corrected for 'reduced QED' radiative corrections. Statistical errors only.
The data are corrected for 'reduced QED' radiative corrections. Statistical errors only.
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Using data from Fermilab fixed-target experiment E769, we have measured particle-antiparticle production asymmetries for Lambda0 hyperons in 250 GeV/c pi+-, K+- and p -- nucleon interactions. The asymmetries are measured as functions of Feynman-x (x_F) and p_t^2 over the ranges -0.12<=x_F<=0.12 and 0<=p_t^2<=3 (GeV/c)^2 (for positive beam) and -0.12<=x_F<=0.4 and 0<=p_t^2<=10 (GeV/c)^2 (for negative beam). We find substantial asymmetries, even at x_F around zero. We also observe leading-particle-type asymmetries. These latter effects are qualitatively as expected from valence-quark content of the target and variety of projectiles studied.
LAMBDA production asymmetries versus XL for the positive beams.
LAMBDA production asymmetries versus PT**2 for the positive beams.
LAMBDA production asymmetries versus XL for the negative beams.
We have measured, at an average centre-of-mass energy of 34.22 GeV a forward-backward charge asymmetry in the reaction e + e − → μ + μ − of value −0.161 ± 0.032. This demonstrates the existence of an axial vector neutral current with coupling strength of g e a g μ a =0.53 ± 0.10. We have also obtained a limit on the vector coupling strength of g e v g μ v <0.12. The Weinberg angle is found to be sin 2 θ W =0.29 +0.09 −0.11 . From the reaction e + e − → τ + τ − we have found g e a g τ a <0.34, g e v g τ v <0.55.
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The dissociation of virtual photons, $\gamma^{\star} p \to X p$, in events with a large rapidity gap between $X$ and the outgoing proton, as well as in events in which the leading proton was directly measured, has been studied with the ZEUS detector at HERA. The data cover photon virtualities $Q^2>2$ GeV$^2$ and $\gamma^{\star} p$ centre-of-mass energies $40<W<240$ GeV, with $M_X>2$ GeV, where $M_X$ is the mass of the hadronic final state, $X$. Leading protons were detected in the ZEUS leading proton spectrometer. The cross section is presented as a function of $t$, the squared four-momentum transfer at the proton vertex and $\Phi$, the azimuthal angle between the positron scattering plane and the proton scattering plane. It is also shown as a function of $Q^2$ and $\xpom$, the fraction of the proton's momentum carried by the diffractive exchange, as well as $\beta$, the Bjorken variable defined with respect to the diffractive exchange.
The differential cross section DSIG/DT for the LRG and the LPS data samples.
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The fitted exponential slope of the T distribution as a function of X(NAME=POMERON).
The Mark J Collaboration at the DESY e+e− collider PETRA presents results on the electroweak reactions e+e−→μ+μ−τ+τ−,μ+μ−γ, and e+e−μ+μ−. The c.m. energy range is 12 to 46.78 GeV. In the μ+μ− and τ+τ− channels the total cross sections and the forward-backward asymmetries are reported and compared with other experiments. The results are in excellent agreement with the standard model. The weak-neutral-current vector and axial-vector coupling constants are determined. The values for muons and τ’s are compatible with universality and with the predictions of the standard model. In the μ+μ−γ channel, all measured distributions, including the forward-backward muon asymmetry, are in excellent agreement with the electroweak theory. Our data on the two-photon process, e+e−μ+μ−, agrees with QED to order α4 over the entire energy range and the Q2 range from 0.7 to 166 GeV2.
SIG(QED) = 86.85/S.
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We measure forward cross sections for production of D+, D0, Ds, D*+, and Λc in collisions of π±, K±, and p on a nuclear target. Production induced by different beam particles is found to be the same within statistics. Strange and baryonic final states are seen to contribute appreciably to the total charm cross section, which our measurements indicate is larger than but consistent with QCD predictions. The energy dependence mapped out by these and previous measurements is consistent with theory. Leading-particle asymmetry measurements for K and p-induced charm production are also presented.
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We use the reaction e+e−→μ+μ−, in the Mark J detector at the DESY high-energy e+e− collider PETRA, to test the standard electroweak theory and find good agreement. We also set limits on the parameters of several extended gauge theories.
CROSS SECTION MEASUREMENT RELATIVE TO PREDICTED QED CROSS SECTION.
FORWARD-BACKWARD ASYMMETRY. THE SYSTEMATIC ERROR IN THE ASYMMETRY IS <0.5 PCT.
ANGULAR DISTRIBUTIONS NOT GIVEN IN PAPER. SUPPLIED BY E.DEFFUR.
The reaction (e+e−→μ+μ−) has been measured between\(\sqrt S= 14.0\) and\(\sqrt S= 36.4\). The total cross section result is in good agreement with the QED prediction and the following Λ values have been obtained:Λ+=186 GeV,Λ−=101 GeV. The angular distribution at high energy (\(\left( {\left. {\left\langle {\sqrt S } \right.} \right\rangle= 34.2 GeV} \right)\)) shows a fitted charge asymmetry of −0.064±0.064 in agreement with theW-S model prediction of −0.092, corresponding to an axial coupling parametera2=4ga2=0.69±0.69.
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Errors include contribution from systematics. Result based on fit(1 + cos(theta)**2 + q cos(theta)) to corrected angular distribution.
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