arXiv subjects

J. G. Koerner

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

17 recordsLinked to original sources

arXiv2001

Determination of the strange quark mass from Cabibbo-suppressed tau decays with resummed perturbation theory in an effective scheme

We present an analysis of the m_s^2-corrections to Cabibbo-suppressed tau lepton decays employing contour improved resummation within an effective scheme which is an essential new feature as compared to previous analyses. The whole perturbative QCD dynamics of the tau-system is described by the beta-function of the effective coupling constant and by two gamma-functions for the effective mass parameters of the strange quark in different spin channels. We analyze the stability of our results with regard to high-order terms in the perturbative expansion of the renormalization group functions. A numerical value for the strange quark mass in the MS scheme is extracted m_s(M_τ)=130\pm 27_{exp}\pm 9_{th} MeV. After running to the scale 1 GeV this translates into m_s(1 GeV)=176 \pm 37_{exp}\pm 13_{th} MeV.

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arXiv2000

Strong coupling constant from $τ$ decay within renormalization scheme invariant treatment

We extract a numerical value for the strong coupling constant α_s from the τ-lepton decay rate into nonstrange particles. A new feature of our procedure is the explicit use of renormalization scheme invariance in analytical form in order to perform the actual analysis in a particular renormalization scheme. For the reference coupling constant in the \MSsch-scheme we obtain α_s(M_τ)= 0.3184 \pm 0.0060_{exp} which corresponds to \al_s(M_Z)= 0.1184 \pm 0.0007_{exp} \pm 0.0006_{hq mass}. This new numerical value is smaller than the standard value from $τ$-data quoted in the literature and is closer to \al_s(M_Z)-values obtained from high energy experiments.

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arXiv2000

Exclusive and Inclusive Semileptonic Lambda_b-Decays

In this talk we present theoretical evidence that the exclusive/inclusive ratio of semileptonic Lambda_b-decays exceeds that of semileptonic B-decays, where the experimental exclusive/inclusive ratio amounts to about 66%. We start from the observation that the spectator quark model provides a lower bound on the leading order Isgur-Wise function of the Lambda_b -> Lambda_c transition in terms of the corresponding B -> D,D^* mesonic Isgur-Wise function. Using experimental data for the B -> D,D^* mesonic Isgur-Wise functions this bound is established. Applying a QCD sum rule estimate of the Lambda_b -> Lambda_c transition form factor which satisfy the spectator quark model bound we predict the exclusive/inclusive ratio of semileptonic Lambda_b decay rates to lie in a range between 0.81 and 0.89. We also provide an upper bound on the baryonic Isgur-Wise function which is determined from the requirement that the exclusive rate should not exceed the inclusive rate. Our pre-Osaka results are discussed in the light of new recent preliminary experimental results on the pertinent mesonic and baryonic form factors presented at the Osaka ICHEP 2000 Conference.

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arXiv1999

One-pion transitions between heavy baryons in the constituent quark model

Single pion transitions of S wave to S wave, P wave to S wave and P wave to P wave heavy baryons are analyzed in the framework of the Heavy Quark Symmetry limit (HQS). We use a constituent quark model picture for the light diquark system with an underlying SU(2N_{f}) X O(3) symmetry to reduce the number of the HQS coupling factors required to describe these transitions. We also use the quantum theory of angular momentum to rewrite the one-pion transitions constituent quark model results in a more general form using the 6j- and 9j-symbols. We finally estimate the decay rates of some single pion transitions between charm baryon states.

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arXiv1999

Electromagnetic Transitions of Heavy Baryons in the SU(2N_{f}) X O(3) Symmetry

Radiative decays of heavy baryons are analyzed within the Heavy Quark Symmetry (HQS). It is shown that employing the light-diquark symmetries, the number of electromagnetic couplings among S-wave and P-wave states as well as those between P-wave to S-wave transitions can be reduced significantly. Using this constituent quark model picture the phenomenological implications of some of these decay modes are, also, discussed.

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arXiv1999

Asymptotic structure of perturbative series for $τ$ lepton decay observables: $m_s^2$ corrections

In a previous paper we performed an analysis of asymptotic structure of perturbation theory series for semileptonic $τ$-lepton decays in massless limit. We extend our analysis to the Cabibbo suppressed $ΔS=1$ decay modes of the $τ$ lepton. In particular we address the problem of $m_s^2$ corrections to theoretical formulas. The properties of the asymptotic behavior of the finite order perturbation theory series for the coefficient functions of the $m_s^2$ corrections are studied.

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arXiv1999

Asymptotic structure of perturbative series for tau lepton observables

We analyze tau lepton decay observables, namely moments of the hadronic spectral density in the finite energy interval (0,M_τ), within finite order perturbation theory including α_s^4 corrections. The start of asymptotic growth of perturbation theory series is found at this order in a scheme invariant manner. We establish the ultimate accuracy of finite order perturbation theory predictions and discuss the construction of optimal observables.

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arXiv1998

On the running electromagnetic coupling constant at $M_Z$

We present a discussion on how to define the running electromagnetic coupling constant at $M_Z$ or some other intermediate scale as e.g. $m_Υ$. We argue that a natural definition consistent with general requirements of the renormalization group should be based on Euclidean values of the momentum of the photon propagator as the appropriate scale. We demonstrate in an explicit example of evaluating the running coupling constant at the scale of the $Υ$ resonance mass that the usual definition of the hadronic contribution with a principal value prescription is inconsistent. In the determination of the value of $α$ at $M_Z$ the numerical difference due to using a Euclidean definition rather than the principal value one is comparable in size to the errors caused by existing experimental and QCD inputs to the evaluation of $α(M_Z)$.

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arXiv1998

Single Pion Transitions of Charmed Baryons

The $SU(2N_{f}) X O(3)$ constituent quark model symmetry of the light diquark system are used to analyze single pion transitions of S-wave to S-wave and P-wave to S-wave heavy baryons. We show that the Heavy Quark Symmetry (HQS) coupling factors are given in terms of the three independent couplings $g_{Σ_Q Λ_Q π}, f_{Λ_{Q1} Σ_Q π}$ and $f_{Λ^{*}_{Q1} Σ_Q π}$. Light-Front quark model spin wave functions are, then, employed to calculate these couplings and to predict decay rates of single pion transitions between charm baryon states.

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arXiv1998

Charmed Baryon Strong Coupling Constants in a Light-Front Quark Model

Light-Front quark model spin wave functions are employed to calculate the three independent couplings g_{Σ_c Λ_c π}, f_{Λ_{c1} Σ_c π} and f_{Λ^{*}_{c1} Σ_c π} of S-wave to S-wave and P-wave to S-wave one-pion transitions. It is found that g_{Σ_c Λ_c π}=6.81 MeV^{-1}, f_{Λ_{c1} Σ_c π}=1.16 and f_{Λ^{*}_{c1} Σ_c π}=0.96 . 10^{-4} MeV^{-2}. We also predict decay rates for specific strong transitions of charmed baryons.

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arXiv1994

Heavy Baryons: Current, Pion and Photon Transtions

We 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 ${\scriptstyle m_Q\rightarrow \infty}$. Our discussion involves the ground state $s$-wave heavy baryons as well as the excited $p$-wave heavy baryon states.

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arXiv1994

Heavy baryons

We review the experimental and theoretical status of baryons containing one heavy quark. The charm and bottom baryon states are classified and their mass spectra are listed. The appropriate theoretical framework for the description of heavy baryons is the Heavy Quark Effective Theory, whose general ideas and methods are introduced and illustrated in specific examples. We present simple covariant expressions for the spin wave functions of heavy baryons including p--wave baryons. The covariant spin wave functions are used to determine the Heavy Quark Symmetry structure of flavour--changing current--induced transitions between heavy baryons as well as one--pion and one--photon transitions between heavy baryons of the same flavour. We discuss $1/m_Q$ corrections to the current--induced transitions as well as the structure of heavy to light baryon transitions. Whenever possible we attempt to present numbers to compare with experiment by making use of further model--dependent assumptions as e.g. the constituent picture for light quarks. We highlight recent advances in the theoretical understanding of the inclusive decays of hadrons containing one heavy quark including polarization. For exclusive semileptonic decays we discuss rates, angular decay distributions and polarization effects. We provide an update of the experimental and theoretical status of lifetimes of heavy baryons and of exclusive nonleptonic two body decays of charm baryons.

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arXiv1994

l=0 to l=1 Transition Form Factors

A method is proposed to extend the hard scattering picture of Brodsky and Lepage to transitions between hadrons with orbital angular momentum l=0 and l=1. The use of covariant spin wave functions turns out to be very helpful in formulating that method. As a first application we construct a light-cone wave function of the nucleon resonance $N^*(1535)$ in the quark-diquark picture. Using this wave function and the extended hard scattering picture, the $N$--$N^*$ transition form factors are calculated at large momentum transfer and the results compared to experimental data. As a further application of our method we briefly discuss the $π$--$a_1$ form factors in an appendix.

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arXiv1993

Hadrons of Arbitrary Spin and Heavy Quark Symmetry

We present a general construction of the spin content of the Bethe-Salpeter amplitudes (covariant wave functions) for heavy hadrons with arbitrary orbital excitations, using representations of the Lorentz group. These wave functions incorporate the symmetries manifest in the heavy quark limit. In the baryonic sector we clearly differentiate between the $Λ$ and $Σ$ type excited baryons. We then use the trace formalism to evaluate the weak transitions of ground state heavy hadrons to arbitrary excited heavy hadrons. The contributions of excited states to the Bjorken sum rule are also worked out in detail.

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arXiv1993

Complete angular analysis of the decay cascade $B \rightarrow D^{**}( \rightarrow D^*(\rightarrow D π) + π) + W(\rightarrow l ν)$

We develop a general algorithm for describing angular decay distributions in cascade decay chains of arbitrary length. The general algorithm is used to study joint angular decay distributions for the cascade decay $B\rightarrow D^{**}( \rightarrow D^*(\rightarrow D π)+π) + W(\rightarrow lν)$ where the $D^{**}$ is a generic $P$-wave charm meson state. Lepton mass effects are fully incorporated

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arXiv1993

Leptonic Flavor-changing Z0 Decays in SU(2)xU(1) Theories with Right- handed Neutrinos

We analyze possible lepton-flavor-violating decays of the $Z^0$ particle in a minimal extension of the Standard Model, in which one right-handed neutral field for each family has been introduced. Such rare leptonic decays are induced by Majorana neutrinos at the first electroweak loop level and are generally not suppressed by the ordinary "see-saw" mechanism. In particular, we find that experimental bounds on branching ratios of the order of $10^{-5}-10^{-6}$ attainable at $LEP$ may impose constraints on lepton-flavor-mixing parameters and the masses of the heavy Majorana neutrinos.

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arXiv1993

Leptonic CP Asymmetries in Flavor-changing H0 Decays

Leptonic flavor-changing $H^0$ decays with branching ratios of the order of $10^{-5}-10^{-6}$ may constitute an interesting framework when looking for large $CP$-violating effects. We show that leptonic $CP$~asymmetries of an intermediate $H^0$ boson can be fairly large in natural scenarios of the minimal Standard Model ($SM$) with right-handed neutrinos, at a level that may be probed at future $H^0$~factories.

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