No Arabic abstract
We examine the O(alpha_s) forward-backward asymmetries for the production process e+ e- --> gamma,Z --> q qbar (g), tagging the outgoing heavy-quark jet at center-of-momentum energies off the Z-peak. The complicated analytic results are reduced to simple polynomial forms that provide excellent approximations. For charm and bottom quark, a full dynamical cancellation gives O(alpha_s) zeros in the forward-backward asymmetry close to the Z-peak. We conclude with a detailed numerical analysis of our results.
Preliminary but close to final results on the Z lineshape and Forward-Backward asymmetries from the four LEP experiments are presented. Combined values extracted from ALEPH. DELPHI, L3 and OPAL data recorded at energies around the Z pole are discussed.
The massive one-loop {it QCD} corrections to the production cross sections of We present the massive one-loop {it QCD} corrections to the production cross sections of polarized quarks in the annihilation process $e^+e^-to qbar{q}(g)$ for bottom, top, and charm quarks. From the full analytical expressions for the production cross sections, Schwinger-type interpolation formulae for all parity-parity combinations $(VV, V!A, AA)$ are derived. The parity-odd interpolation formula contains the correct limit for vanishing quark masses taking into account a residual coupling of left- and right-chiral states in the massless theory. Numerical results for the total cross section and the longitudinal spin polarization demonstrate the accuracy of the interpolation formulae.
We review in some detail the QCD corrections to the measurement of the forward-backward charge asymmetry of heavy quarks in the $mathrm{e^+e^-rightarrow Qoverline{Q}(g)}$ process at the Z pole. We show that the size of these corrections can be reduced by an order of magnitude by using simple cuts on jet acollinearity. Such a reduction is expected to lead to systematic uncertainties at the $Delta mathrm{A_{FB}^{0,Q}} approx 10^{-4}$ level, opening up the path to high precision electroweak measurements with heavy flavors at future high luminosity $mathrm{e^+e^-}$ colliders like the FCC-ee.
In the asymptotic limit $Q^2 gg m^2$, the heavy flavor Wilson coefficients for deep--inelastic scattering factorize into the massless Wilson coefficients and the universal heavy flavor operator matrix elements resulting from light--cone expansion. In this way, one can calculate all but the power corrections in $(m^2/Q^2)^k, k > 0$. The heavy flavor operator matrix elements are known to ${sf NLO}$. We present the last 2--loop result missing in the unpolarized case for the renormalization at 3--loops and first 3--loop results for terms proportional to the color factor $T_F^2$ in Mellin--space. In this calculation, the corresponding parts of the ${sf NNLO}$ anomalous dimensions cite{LARIN,MVVandim} are obtained as well.
We calculate the longitudinal contribution to the alignment polarization $Pl$ of quarks produced in $e^+e^-$ annihilation. In the Standard Model, the longitudinal alignment polarization vanishes at the Born term level and thus receives its first non-zero contribution from the $O(as)$ tree graph process. We provide analytical and numerical results for the longitudinal alignment polarization of massless and massive quarks, in particular for the recently discovered top quark.