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J. G. Körner

Publications and source records attributed to J. G. Körner.

82 records · Page 5Linked to original sources
arXiv1996

Transverse Polarization of Top Quarks Produced in e+e- Annihilation at O(alpha_s)

We present the results of an O(alpha_s) calculation of the transverse polarization of top quarks produced in e+e- annihilation. In a first step we determine the transverse polarization of the top with regard to the hadron plane spanned by the (q,bar q,g) system. We then rotate the transverse components of the polarization to the lepton plane spanned by the (q,e+,e-) system. After azimuthal averaging we determine the three remaining inclusive transversely polarized structure functions. Together with the one-loop and Born term contributions they determine the sin(theta) and sin(2*theta) beam-quark polar angle dependence of the transverse polarization. We present analytic and numerical results for the polarized structure functions and the polar angle dependence of the transverse polarization. We briefly comment on the transverse polarization of bottom quarks produced in e+e- annihilation.

hep-ph↗
arXiv1996

QCD Sum Rules for Heavy Baryons at Next-to-Leading Order in alpha_s

We derive QCD sum rules for heavy baryons at leading order in $1/m_Q$ and at next-to-leading order in $α_s$. The calculation involves the evaluation of four different perturbative three-loop diagrams which determine the $α_s$-corrections to the Wilson coefficients of the leading term in the Operator Product Expansion (OPE). From the sum rules we obtain estimates for the masses and the residues of the heavy baryons $Λ_Q$ and $Σ_Q$. The perturbative $O(α_s)$ corrections to the leading order spectral function amount to about $100%$, and they shift the calculated values for the baryon masses slightly upward. The residues are shifted upward by about $20-50%$. For the bound state energy $\barΛ$ given by the difference of the heavy baryon mass and the pole mass of the heavy quark $m_Q$ we obtain $m_{Λ_Q}-m_Q=780 MeV$ and $m_{Σ_Q}-m_Q=950 MeV$. For the residues we find $|F_Λ|=0.028 GeV^3$ and $|F_Σ|=0.039 GeV^3$.

hep-ph↗
arXiv1996

Constituent Quark Model Approach to Heavy Baryon Transitions

I discuss the structure of current-induced bottom baryon to charm baryon transitions, and the structure of pion and photon transitions between heavy charm or bottom baryons in the Heavy Quark Symmetry (HQS) limit as $m_Q\rightarrow\infty$. By doing a spin-parity analysis I derive a general formula which allows one to enumerate the independent HQS amplitudes in the three types of transitions. I go on to show that use of the constituent quark model for the light-side diquark transitions leads to a considerable reduction in the number of independent amplitudes derived in the HQS limit. The discussion includes the ground state $s$-wave as well as the $p$-wave heavy baryons.

hep-ph↗
arXiv1996

Two-loop Anomalous Dimensions of Heavy Baryon Currents in Heavy Quark Effective Theory

We present results on the two-loop anomalous dimensions of the heavy baryon HQET currents $J=(q^TCΓτq)Γ'Q$ with arbitrary Dirac matrices $Γ$ and $Γ'$. From our general result we obtain the two-loop anomalous dimensions for currents with quantum numbers of the ground state heavy baryons $Λ_Q$, $Σ_Q$ and $Σ_Q^*$. As a by-product of our calculation and as an additional check we rederive the known two-loop anomalous dimensions of mesonic scalar, pseudoscalar, vector, axial vector and tensor currents $(J=\bar qΓq)$ in massless QCD as well as in HQET.

hep-ph↗
arXiv1995

Improved variables for measuring the $Lambda_b$ polarization

We discuss a few possible strategies for measuring the polarization of the $Λ_{\mathrm{b}}$ baryons produced in $e^+e^-$-annihilation at the $\mathrm{Z}$ resonance through their inclusive semileptonic decays. After reviewing the existing methods, a new method is proposed, based on the ratio of the averages of the squared electron and neutrino energy, including both perturbative and nonperturbative corrections. This variable minimizes the statistical error on the $Λ_{\mathrm{b}}$ polarization, while keeping the systematic theoretical errors at the level of 1-2%. A number of other polarization-sensitive variables are also discussed, such as averages of ratios of the electron and neutrino energy and the distribution in the difference of the electron and neutrino rapidities.

hep-ph↗
arXiv1995

Two -loop $O(G_F{M_H}^2)$ radiative corrections to the Higgs decay width $H \to γγ$ for large Higgs boson masses

This note is devoted to the calculation of the two-loop $O(G_F {M_H}^2)$ radiative corrections to the Higgs decay width $H \to γγ$ for large values of the Higgs boson mass $M_H$ within the Minimal Standard Model. The use of the Equivalence Theorem makes it possible to reduce the problem to the consideration of the physical Higgs boson field and the Goldstone bosons $w^{+},w^{-},z$. We present analytical results for the various two- and three-particle absorptive parts of two-loop contributions, using dispersive techniques, analytic results for all but one of the dispersive contributions. The typical size of the correction is $\sim ~30 $ percent for a Higgs boson mass of order $1~TeV$.

hep-ph↗
arXiv1995

$SU(2N_{f})\otimes O(3)$ light diquark symmetry and current-induced heavy baryon transition form factors

We study the current-induced bottom baryon to charm baryon transitions in the Heavy Quark Symmetry limit as $m_{q}\rightarrow \infty$. Our discussion involves $s$-wave to $s$-wave as well as $s$-wave to $p$-wave transitions. Using a constituent quark model picture for the light diquark system with an underlying $SU(2N_{f})\otimes O(3)$ symmetry and the heavy quark symmetry we arrive at a number of new predictions for the reduced form factors that describe these transitions.

hep-ph↗
arXiv1995

QCD Radiative Correction to Zero Recoil Sum Rules for Heavy Flavor Transitions in the Small Velocity Limit.

We consider the small velocity sum rules for heavy flavour semileptonic transitions that are used to estimate the zero recoil values of semileptonic heavy flavour form factors. We analyze the complete O($α_S$) radiative correction to these sum rules. The corrections are universal and influence all "model-independent" bounds previously derived for semileptonic form factors at zero recoil.

hep-ph↗
arXiv1993

QCD corrections to decays of polarised charm and bottom quarks

Distributions of charged leptons in semileptonic $Λ_c$ and $Λ_b$ decays can be used as spin analysers for the corresponding charm and bottom quarks. QCD corrections to the energy spectra of charged leptons have been given in the literature as well as the corrections to the angular dependence for polarised up-type quarks. The analogous formulae are derived also for polarised down-type quarks. These results are applied to the decays of polarised charm and bottom quarks. The corrections to the asymmetries are found to be small for charm decays. For bottom decays they exhibit a non-trivial dependence on the energy of the charged lepton.

hep-ph↗