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Register a new userO(alpha_s) Spin-Spin Correlations for Top and Bottom Quark Production in e+ e- Annihilation
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We present the full O(alpha_s) longitudinal spin-spin correlations for heavy-quark pair production at e+ e- high-energy colliders in closed analytical form. In such reactions, quark and antiquark have strongly correlated spins, and the longitudinal components are dominant. For the explicit computation of the QCD bremsstrahlung contributions, new phase-space integrals are derived. Explicit numerical estimates are given for t t_bar and b b_bar production. Around the Z-peak, QCD one-loop corrections depolarize the spin-spin asymmetry for bottom quark pairs by approximately -4%. For top pair production, we find at 350GeV a 0.6% increased polarization over a value of 0.4 in the longitudinal correlation. For more than 1 TeV the O(alpha_s) corrections enhance depolarization to -2% in the top-pair case.
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We present a new derivation of the O(alpha_s) angular distribution of the outgoing $q$-quark in the production process $e^+ e^- togamma,Zto q,bar{q}(g)$. In our calculation, we express the three-particle phase-space integration of the gluon-bremsstrahlung process in terms of a general set of analytic integral solutions. A consistent treatment of the QCD one-loop corrections to the axial-vector current deserves special attention. This is relevant in the derivation of the forward-backward asymmetry predicted by the standard model. Finally, we provide the full analytical solutions for the differential rates in closed form and conclude with numerical estimates for bottom and top quark production.
We present a detailed investigation of the NLO polarization of the top quark in t t-bar production at a polarized linear e^+ e^- collider with longitudinally polarized beams. By appropiately tuning the polarization of the beams one can achieve close to maximal values for the top quark polarization over most of the forward hemisphere for a large range of energies. This is quite welcome since the rate is largest in the forward hemisphere. One can also tune the beam polarization to obtain close to zero polarization over most of the forward hemisphere.
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.
In this talk I first present a short review of fluctuations in $e^+e^-$-annihilations. I then describe some new results on FD correlations. Experimental analyses of $pp$ and $LambdaLambda$ correlations indicate a very small production radius. This result relies very strongly on comparisons with MC simulations. A study of the approximations and uncertainties is these simulations imply that it is premature to draw such a conclusion from the data.
We point out that the fragmentation of a strange quark into nucleons versus antinucleons is not necessarily identical $D_{p/s}(z,Q^2) eq D_{bar p/s}(z,Q^2)$, even though the perturbative contributions from gluon splitting and evolution are $p leftrightarrow bar p$ symmetric. The observation of such asymmetries in the hadronization of strange and other heavy quarks can provide insight into the nonperturbative mechanisms underlying jet fragmentation in QCD.
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