arXiv subjects

Jürgen G. Körner

Publications and source records attributed to Jürgen G. Körner.

28 records · Page 2Linked to original sources

arXiv2017

Analyzing New Physics in $\bar{B}^0 \to D^{(\ast)}τ^-\barν_τ$

We discuss possible new physics (NP) effects beyond the standard model (SM) in the exclusive decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$. Starting with a model-independent effective Hamiltonian including non-SM four-Fermi operators, we show how to obtain experimental constraints on different NP scenarios and investigate their effects on a large set of physical observables. The $\bar{B}^0 \to D^{(\ast)}$ transition form factors are calculated in the full kinematic $q^2$ range by employing the covariant confined quark model developed by our group.

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arXiv2017

Probing new physics in $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$ using the longitudinal, transverse, and normal polarization components of the tau lepton

We study the longitudinal, transverse, and normal polarization components of the tau lepton in the decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$ and discuss their role in searching for new physics (NP) beyond the standard model (SM). Starting with a model-independent effective Hamiltonian including non-SM four-Fermi operators, we obtain experimental constraints on different NP scenarios and investigate their effects on the polarization observables. In the SM the longitudinal and transverse polarizations of the tau lepton differ substantially from the corresponding zero lepton mass values of $P_L=-1$ and $P_T=0$. In addition, $P_L$ and $P_T$ are very sensitive to NP effects. For the transverse polarization this holds true, in particular, for the effective tensor operator in the case of $\bar{B}^0 \to D^\ast$ and for the scalar operator in the case of $\bar{B}^0 \to D$. The $T$-odd normal polarization $P_N$, which is predicted to be negligibly small in the SM, can be very sizable assuming NP complex Wilson coefficients. We also discuss in some detail how the three polarization components of the tau lepton can be measured with the help of its subsequent leptonic and semihadronic decays.

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arXiv2016

Analyzing new physics in the decays $\bar{B}^0 \to D^{(\ast)}τ^-\barν_τ$ with form factors obtained from the covariant quark model

We study possible New Physics (NP) effects in the exclusive decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$. We extend the Standard Model (SM) by taking into account right-handed vector (axial), left- and right-handed (pseudo)scalar, and tensor current contributions. The $\bar{B}^0 \to D^{(\ast)}$ transition form factors are calculated in the full kinematic $q^2$ range by employing a covariant quark model developed by us. We provide constraints on NP operators based on measurements of the ratios of branching fractions $R(D^{(\ast)}) \equiv \mathcal{B}(\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ)/ \mathcal{B}(\bar{B}^0 \to D^{(\ast)} μ^- \barν_μ)$ and consider the effects of these operators on physical observables in different NP scenarios. We also derive the four-fold angular distribution for the cascade decay $\bar {B}^0\to D^{\ast\,+}(\to D^0π^+)τ^-\barν_τ$ which allows one to analyze the polarization of the $D^{\ast}$ meson in the presence of NP effects. We discuss several strategies to distinguish between various NP contributions.

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arXiv2015

Exclusive decays $B \to \ell^-\barν$ and $B \to D^{(\ast)}\ell^-\barν$ in the covariant quark model

We study the exclusive leptonic and semileptonic $B$ decays $B \to \ell^- \barν$ and $B \to D^{(\ast)} \ell^-\barν$ in the framework of the covariant quark model with built-in infrared confinement. We compute the relevant form factors in the full kinematical momentum transfer region. The calculated form factors are used to evaluate branching fractions and polarization observables of the above transitions. We compare our results with experimental data and results from other theoretical studies.

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arXiv2015

Physical observables in the decay $Λ_b \to Λ_c (\to Λ+π)+τ^{-}+\bar ν_τ$

We analyze the tauonic semileptonic baryon decays $Λ^0_b \to Λ^+_c + τ^{-} +\bar ν_τ$ with particular emphasis on the lepton helicity flip contributions which vanish for zero lepton masses. We calculate the total rate, differential decay distributions, the longitudinal and transverse polarization components of the $Λ^+_c$ and the $τ^-$, and the lepton-side forward-backward asymmetries. We use the covariant confined quark model to provide numerical results on these observables.

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arXiv2015

Lepton-mass effects in the decays $H \to ZZ^{\ast} \to \ell^{+} \ell^{-} τ^{+} τ^{-}$ and $H \to WW^{\ast} \to \ell ντν_τ$

We consider lepton-mass effects in the cascade decays $H\to Z(\to \ell^{+} \ell^{-})+Z^{\ast}(\to τ^{+}τ^{-})$ and $H\to W^{-}(\to \ell^{-}\bar ν_{\ell})+W^{+\ast}(\to τ^{+}ν_τ)$. Since the scale of the problem is set by the off-shellness $q^{2}$ of the respective gauge bosons in the limits $(m_{\ell}+m_{\ell'})^{2} \le q^{2} \le (m_{H}-m_{W,Z})^{2}$ and not by $m_{W,Z}^{2}$, lepton-mass effects are non-negligible for the $τ$ modes in particular close to the threshold of the off-shell decays. Lepton-mass effects show up e.g.\ in the three-fold joint angular decay distribution for the decays. Nonzero lepton masses lead to leptonic helicity-flip contributions which in turn can generate novel angular dependencies in the respective three-fold angular decay distributions. Lepton-mass effects are more pronounced in the $H \to Z(\to \ell\ell)Z^{\ast}(\toττ)$ mode which, in part, is due to the fact that the ratio of lepton helicity flip/nonflip contributions in the decay $Z^{\ast} \to \ell^{+}\ell^{-}$ is four times larger than in the decay $W^{+\ast}\to \ell^{+}ν$. We also briefly consider the corresponding off-shell -- off-shell decays $H\to Z^{\ast}(\to \ell^{+}\ell^{-})+Z^{\ast}(\to τ^{+}τ^{-})$ and $H\to W^{-\ast}(\to \ell^{-}\bar ν_{\ell})+W^{+\ast}(\to τ^{+}ν_τ)$.

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arXiv2004

Towards a NNLO calculation in hadronic heavy hadron production

We calculate the Laurent series expansion up to ${\cal O}(ε^2)$ for all scalar one-loop one-, two-, three- and four-point integrals that are needed in the calculation of hadronic heavy flavour production. The Laurent series up to ${\cal O}(ε^2)$ is needed as input to that part of the NNLO corrections to heavy hadron production at hadron colliders where the one-loop integrals appear in the loop-by-loop contributions. The four-point integrals are the most complicated. The ${\cal O}(ε^2)$ expansion of the four-point integrals contains polylogarithms up to $ Li_4$ and the multiple polylogarithms.

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arXiv2004

Complete O(α) solution of the μ-decay problem

In this talk I report on the results of a complete O(α) calculation of leptonic μ-decay. The calculation is complete in the sense that all polarization and mass effects have been included in the radiative corrections. I mostly concentrate on the longitudinal polarization of the electron which considerably differs from the naive value P_e^l=-1 in the threshold region, both for the Born term and more so for the radiatively corrected case. I also discuss the role of the O(α) anomalous spin-flip contribution and its description in terms of the equivalent particle approach which survives the m_e -> 0 limit. Finally, I provide a brief account of the history of the O(α) radiative corrections to leptonic μ-decay. I trace the error done in the first (wrong) 1956 calculation of Behrends, Finkelstein and Sirlin. My account of this historical error differs from that recently given in a talk by Kinoshita on the occasion of the 70th birthday of Sirlin.

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arXiv1999

Spin-Momentum Correlations in Inclusive Semileptonic Decays of Polarized $Λ_b$ Baryons

We consider spin-momentum correlations between the spin of the bottom baryon $Λ_{\mathrm{b}}$ and the momenta of its decay products in its inclusive semileptonic decay. We define several polar and azimuthal spin-momentum correlation measures in different event coordinate systems. The values of the spin-momentum correlation measures are calculated up to ${\cal O}(1/m_b^2)$ using the standard OPE und HQET methods. Some of the measures turn out to be sufficiently large to make them good candidates for a determination of the polarization of the $Λ_{\mathrm{b}}$ in e.g. $\mathrm{Z}$ decays.

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arXiv1996

Issues in Heavy Flavour Baryons

I present a mini-review on the physics of heavy flavour baryons where I concentrate on the HQET description of their exclusive decay modes. In particular 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 limit as m_Q->\infty. The emphasis is on the structural similarity of the Heavy Quark Symmetry predictions for the three types of transitions. The requisite coupling expressions are discussed both in the covariant framework as well as in terms of Clebsch-Gordan coefficients and 6-j symbols. At the end of my review I touch on some unresolved issues in exclusive nonleptonic charm and bottom baryon decays which serve to highlight our present lack of understanding of nonleptonic heavy baryon decays.

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