A high-precision measurement of the differential cross section for Bhabha scattering (e+e−→e+e−) is presented. The measurement was performed with the MAC detector at the PEP storage ring of the Stanford Linear Accelerator Center, at a center-of-mass energy of 29 GeV. Effects due to electroweak interference are observed and agree well with the predictions of the Glashow-Salam-Weinberg model. The agreement between the data and the electroweak prediction rules out substructure of the electron up to mass scales of 1 TeV.
Error contains both statistics and systematics.
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A high-statistics measurement has been made of the process e+e−→μ+μ− at s=29 GeV with the MAC detector at the SLAC storage ring PEP. The electroweak forward-backward charge asymmetry for a sample of approximately 16 000 events was measured to be Aμμ=−0.063±0.008±0.002. The ratio of the cross section to the lowest-order QED cross section was measured to be Rμμ=1.01±0.01±0.03. From these results the weak neutral axial-vector and vector couplings are determined to be gAegAμ=0.25±0.03±0.01 and gVegVμ=−0.02±0.03±0.09.
Data are fully corrected, including radiative effects.
Asymmetry determined from a two parameter fit to the angular distribution proportional to R*(1 + cos(theta)**2 + (8/3)*A*cos(theta)). R is then the total ratio relative to the lowest order QED cross section and A is the forward-backward asymmetry.
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A high-statistics measurement is presented of the cross section for the process e+e−→τ+τ− at s=29 GeV from the MAC detector at PEP. A fit to the angular distribution of our sample of 10 153 events with |cosθ|<0.9 gives an asymmetry Aττ=−0.055±0.012±0.005 from which we find the product of electron and tau axial-vector weak neutral couplings gAegAτ=0.22±0.05.
Data fully corrected up to O(ALPHA**3) radiative effects. Data requested from authors.
Data extrapolated to full acceptance.
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We report a high-precision measurement of the ratio R of the total cross section for e+e−→hadrons to that for e+e−→μ+μ−, at a center-of-mass energy of 29.0 GeV using the MAC detector. The result is R=3.96±0.09. This value of R is used to determine a value of the strong coupling constant αs of 0.23±0.06, nearly independent of fragmentation models. Two different analysis methods having quite different event-selection criteria have been used and the results are in agreement. Particular attention has been given to the study of systematic errors. New higher-order QED calculations are used for the luminosity determination and the acceptance for hadrons.
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A measurement of the cross section for production of collinear muon pairs based upon a sample of about 3000 events observed in the MAC detector at the storage ring PEP is presented. From the angular asymmetry Aμμ=0.076±0.018 the axial-vector weak neutral coupling is found to be given by gAegAμ=0.31±0.08.
Data on non-collinearity and angular distribution.
Asymmetry measurement based on extrapolation of number of events to 4 PI acceptance.
A study of the lateral development of jets of hadrons produced in electron-positron annihilation has been used to determine the strong coupling constant αs. Data were obtained with the MAC detector at the SLAC e+e− storage ring PEP at s=29 GeV. Based on the parton calculations of Gottschalk and Shatz, a value for αs of 0.133±0.005(stat)±0.009(syst) has been determined for string fragmentation, and 0.112±0.008(stat)±0.007(syst) for an independent-jet model.
JET FRACTION MEASURED. FIT ACCORDING TO:. T.D. GOTTSCHALK AND M.P.SCHATZ CALT-68-1172 (1985).
JET FRACTION MEASURED. FIT ACCORDING TO INDEPENTENT JET MODEL.
We present measurements of forward-backward energy asymmetries of τ-lepton decay products from the reaction e+e−→τ+τ− in data collected with the MAC detector operating at the SLAC storage ring PEP at a center-of-mass energy of 29 GeV. The energy asymmetries for the decays τ→ντeν¯e, τ→ντμν¯μ, τ→ντπ, and τ→ντρ are interpreted as effects caused by the combination of maximally parity-violating weak τ decays and a longitudinal polarization produced by the interference of electromagnetic and weak processes. From the forward-backward polarization asymmetry AP=(0.06±0.07)×(1±0.011), we determine the coupling-constant product gaegvτ=(0.26 ±0.31)×(1±0.011). Assuming gae=-(1/2 as expected, we find gvτ=(-0.52±0.62)×(1±0.011), consistent with the prediction of the Glashow-Weinberg-Salam model of electroweak interactions. Alternatively, assuming the standard-model prediction of negligible polarization in τ-pair production, the leptonic energy spectra are used to measure the Michel parameter to be 0.79±0.10±0.10, consistent with the V-A hypothesis for the τν¯τ-W vertex.
No description provided.
A charge asymmetry has been observed in final-state jets from e+e− annihilation into hadrons at √s =29 GeV. The measured asymmetry is consistent with the prediction of electroweak theory. The product of axial-vector weak coupling constants, averaged over all quark flavors, is determined to be 〈gAegAq〉=-0.34±0.06±0.05.
Measured differential cross section after efficiency and radiative cross sections. THETA is the polar-angle of the thrust axis defined to be the angle between the direction of the incident positron and the thrust axis taken in the direction of the positron jet. Numerical values requested from the authors. Data are normalised to the total expected QED cross section.
High-precision measurements of electron-positron annihilation into final states of two, three, and four photons are presented. The data were obtained with the MAC detector at the PEP storage ring of the Stanford Linear Accelerator Center, at a center-of-mass energy of 29 GeV. The measured e+e−→γγ differential cross section is used to test the validity of quantum electrodynamics (QED) in this energy range; it agrees well with QED, and the limit on cutoff parameters for the electron propagator is Λ>66 GeV. The measurement of e+e−→γγγ is used to test the QED calculations of order α3 and to search for anomalies that would indicate the existence of new particles; the agreement with QED is excellent and no anomalies are found. Two events from the reaction e+e−→γγγγ are found, in agreement with the QED prediction.
Errors are combined statistical and systematics.
No description provided.
Two 4gamma events are observed corresponding to a cross section of 0.02 PB.
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No description provided.