The forward-backward asymmetry of charm quark production has been measured at an average of energy of 58.4 GeV with the VENUS detector at the TRISTAN e + e - collider. The charm quarks were identified through reconstruction of charged D ∗ mesons using the mass difference between the D ∗ and D 0 mesons. The measured charge asymmetry, -0.49 +.019 −0.17 ±0.04, is consistent with the prediction of the standard theory. The corresponding axial-vector coupling constant is 1.03 +0.40 −0.35 ±0.07.
No description provided.
The couplings of the Z 0 to charged leptons are studied using measurements of the lepton pair cross sections and forward-backward asymmetries at centre of mass energies near to the mass of the Z 0 . The data are consistent with lepton universality. Using a parametrisation of the lepton pair differential cross section which assumes that the Z 0 has only vector and axial couplings to leptons, the charged leptonic partial decay width of the Z 0 is determined to be Г ol+ol− = 83.1±1.9 MeV and the square of the product of the effective axial vector and vector coupling constants of the Z 0 to charged leptons to be a ̌ 2 ol v ̌ 2 ol = 0.0039± 0.0083 , in agreement with the standard model. A parametrisation in the form of the improved Born approximation gives effective leptonic axial vector and vector coupling constants a ̌ 2 ol = 0.998±0.024 and v ̌ 2 ol = 0.0044±0.0083 . In the framework of the standard model, the values of the parameters ϱ z and sin 2 θ w are found to be 0.998±0.024 and 0.233 +0.045 −0.012 respectively. Using the relationship in the minimal standard model between ϱ z and sin 2 θ w , the results sin 2 θ SM w = 0.233 +0.007 −0.006 is obtained. Our previously published measurement of the ratio of the hadronic to the leptonic partial width of the Z 0 is update: R z = 21.72 +0.71 −0.65 .
Forward-backward asymmetry corrected for kinematic cuts. Errors have systematics folded.
Forward-backward asymmetry. Statistical errors only.
Forward-backward asymmetry. Statistical errors only.
We have tested extra Z models in the reactions e + e − → μ + μ − , τ + τ − and hadrons in the energy range 50< s <64 GeV using the VENUS detector at the TRISTAN e + e − storage ring. Our data are in good agreement with the standard model prediction ( χ 2 N Df = 2.9 31 ) ). We have obtained 90% confidence-level lower limits of 105, 125 and 231 GeV for the masses of Z Ψ , Z η and Z χ bosons which are expected from the E 6 grand unified theory. We also place a 90% confidence-level lower limit of 426 GeV for the mass of an extra-Z boson whose couplings to quarks and leptons are assumed to be the same as those for the standard Z boson. Our results exceed the previous experimental limits from the p p collider experiments, although there have been some combined analyses reporting the limits better than those obtained in the present analysis.
New measurements. Statistical and systematic errors combined in quadrature.
New measurements.
Combination of selected VENUS data from this and previous publications. Statistical and systematic errors combined in quadrature.
We report a new measurement of the parity-violating asymmetry in elastic electron scattering from the proton at backward scattering angles. This asymmetry is sensitive to the strange magnetic form factor of the proton as well as electroweak axial radiative corrections. The new measurement of A=-4.92 +- 0.61 +- 0.73 ppm provides a significant constraint on these quantities. The implications for the strange magnetic form factor are discussed in the context of theoretical estimates for the axial corrections.
Polarized beam. FORMFACTOR(NAME=GM_S) is the strange quark contribution. FORMFACTOR(NAME=GM_S) is in nucleon magnetic FF.
We have measured the parity-violating electroweak asymmetry in the elastic scattering of polarized electrons from the proton. The kinematic point (theta_lab = 12.3 degrees and Q^2=0.48 (GeV/c)^2) is chosen to provide sensitivity, at a level that is of theoretical interest, to the strange electric form factor G_E^s. The result, A=-14.5 +- 2.2 ppm, is consistent with the electroweak Standard Model and no additional contributions from strange quarks. In particular, the measurement implies G_E^s + 0.39G_M^s = 0.023 +- 0.034 (stat) +- 0.022 (syst) +- 0.026 (delta G_E^n), where the last uncertainty arises from the estimated uncertainty in the neutron electric form factor.
Longitudinally polarized beam. C=L and C=R means left- and right polarization. The second systematic uncertainty arises from the estimated uncertainty inthe neutron electromagnetic from factor.
We report the first measurement of the parity-violating asymmetry in elastic electron scattering from the proton. The asymmetry depends on the neutral weak magnetic form factor of the proton which contains new information on the contribution of strange quark-antiquark pairs to the magnetic moment of the proton. We obtain the value $G_M~Z= 0.34 \pm 0.09 \pm 0.04 \pm 0.05$ n.m. at $Q~2=0.1$ (GeV/c)${}~2$.
Polarized beam. FORMFACTOR(NAME=GZM) = (1/4)*(GM_P-GM_N) - SIN2TW*GM_P - (1/4)*GM_S, whereFORMFACTOR(NAME=GM_S) is the strange quark contribution. FORMFACTOR(NAME=GZM) and FORMFACTOR(NAME=GM_S) are in nucleon magnetic FF.
None
No description provided.
No description provided.
The production of $D_s^-$ relative to $D_s^+$ as a function of $x_F $ with 600 GeV/c $\Sigma^-$ beam is measured in the interval $0.15 < x_F < 0.7$ by the SELEX (E781) experiment at Fermilab. The integrated charge asymmetries with 600 GeV/c $\Sigma^-$ beam ($0.53\pm0.06$) and $\pi^-$ beam ($0.06\pm0.11$) are also compared. The results show the $\Sigma^-$ beam fragments play a role in the production of $D_s^-$, as suggested by the leading quark model.
Production asymmetry for the SIGMA- beam.
Integrated asymmetry (with XL > 0.15) for the PI- and SIGMA- beams.
The polarization of tau leptons in the reaction e+ e- --> tau+ tau- has been measured using a e+e- collider, TRISTAN, at the center-of-mass energy of 58 GeV. From the kinematical distributions of daughter particles in tau --> e nu nu-bar, mu nu nu-bar, rho nu or pi(K) nu decays, the average polarization of tau- and its forward-backward asymmetry have been evaluated to be 0.012 +- 0.058 and 0.029 +- 0.057, respectively.
Charged-conjugated states are included. The forward-backward asymmetry of the polarization is defined as (SIG(F)*POL-SIG(B)*POL)/(SIG(F)*POL+SIG(B)*POL). The last value is the combination of the results for all decay modes. The systematic error is not given.
Using 123 multihadronic inclusive muon-production e+e− annihilation events at an average c.m. energy of 55.2 GeV, we extracted the forward-backward charge asymmetry of the e+e−→bb¯ process and the R ratio for bb¯ production. We used an analysis method in which the behavior of the c quark and lighter quarks is assumed, with only that of the b quark left indeterminate. The results, Ab=-0.72±0.28(stat)±0.13(syst) and Rb=0.57±0.16±0.10, are consistent with the standard model.
Asymmetry in BOTTOM quark production.
Forum