C. Albertus

Charmed and bottom baryons: A Variational approach based on heavy quark symmetry

Abstract The use of heavy quark symmetry to study bottom and charmed baryons leads to important simplifications of the non-relativistic three body problem, which turns out to be easily solved by a simple variational ansatz. Our simple scheme reproduces previous results (baryon masses, charge and mass radii, …) obtained by solving the Faddeev equations with simple non-relativistic quark–quark potentials, adjusted to the light and heavy–light meson spectra. Wave functions, parameterized in a simple manner, are also given and thus they can be easily used to compute further observables. Our method has been also used to find the predictions for strangeness-less baryons of the SU(2) chirally inspired quark–quark interactions. We find that the one pion exchange term of the chirally inspired interactions leads to relative changes of the Λ b and Λ c binding energies as large as 90%.

Semileptonic B -> pi decays from an Omnès improved nonrelativistic constituent quark model

The semileptonic B{yields}{pi}l{sup +}{nu}{sub l} decay is studied starting from a simple quark model which includes the influence of the B* pole. To extend the predictions of a nonrelativistic constituent quark model from its region of applicability near q{sub max}{sup 2}=(m{sub B}-m{sub {pi}}){sup 2} to all q{sup 2} values accessible in the physical decay, we use a novel multiply subtracted Omnes dispersion relation, which considerably diminishes the form-factor dependence on the elastic {pi}B{yields}{pi}B scattering amplitudes at high energies. By comparison to the experimental branching fraction we extract |V{sub ub}|=0.0034{+-}0.0003(exp){+-}0.0007(theory). To further test our framework, we also study D{yields}{pi} and D{yields}K decays and find excellent results f{sub {pi}}{sup +}(0)/f{sub K}{sup +}(0)=0.80{+-}0.03, B(D{sup 0}{yields}{pi}{sup -}e{sup +}{nu}{sub e})/B(D{sup 0}{yields}K{sup -}e{sup +}{nu}{sub e})=0.079{+-}0.008. In particular for the D{yields}{pi} case, we reproduce, with high accuracy, the three-flavor lattice QCD results recently obtained by the Fermilab-MILC-HPQCD Collaboration. While for the D{yields}K case, we successfully describe the data for f{sup +}(q{sup 2})/f{sup +}(0) recently measured by the FOCUS Collaboration.

What does the free space Lambda Lambda interaction predict for Lambda Lambda hypernuclei

Data on LambdaLambda hypernuclei provide a unique method to learn details about the strangeness S = -2 sector of the baryon-baryon interaction. From the free space Bonn-Jülich potentials, determined from data on baryon-baryon scattering in the S = 0,-1 channels, we construct an interaction in the S = -2 sector to describe the experimentally known LambdaLambda hypernuclei. After including short-range (Jastrow) and RPA correlations, we find masses for these LambdaLambda hypernuclei in a reasonable agreement with data, taking into account theoretical and experimental uncertainties. Thus, we provide a natural extension, at low energies, of the Bonn-Jülich one-boson exchange potentials to the S = -2 channel.

What Does the Free SpaceΛΛInteraction Predict forΛΛHypernuclei

Data on LambdaLambda hypernuclei provide a unique method to learn details about the strangeness S = -2 sector of the baryon-baryon interaction. From the free space Bonn-Jülich potentials, determined from data on baryon-baryon scattering in the S = 0,-1 channels, we construct an interaction in the S = -2 sector to describe the experimentally known LambdaLambda hypernuclei. After including short-range (Jastrow) and RPA correlations, we find masses for these LambdaLambda hypernuclei in a reasonable agreement with data, taking into account theoretical and experimental uncertainties. Thus, we provide a natural extension, at low energies, of the Bonn-Jülich one-boson exchange potentials to the S = -2 channel.

Doubly heavy-quark baryon spectroscopy and semileptonic decay

Abstract.Working in the framework of a nonrelativistic quark model we evaluate the spectra and semileptonic decay widths for the ground state of doubly heavy Ξ and Ω baryons. We solve the three-body problem using a variational ansatz made possible by the constraints imposed by heavy-quark spin symmetry. In order to check the dependence of our results on the inter-quark interaction, we have used five different quark-quark potentials which include Coulomb and hyperfine terms coming from one-gluon exchange, plus a confining term. Our results for the spectra are in good agreement with a previous calculation done using a Faddeev approach. For the semileptonic decay our results for the total decay widths are in good agreement with the ones obtained within a relativistic quark model in the quark-diquark approximation.

Combined nonrelativistic constituent quark model and heavy quark effective theory study of semileptonic decays of {lambda}{sub b} and {xi}{sub b} baryons

We present the results of a nonrelativistic constituent quark model study of the semileptonic decays {lambda}{sub b}{sup 0}{yields}{lambda}{sub c}{sup +}l{sup -}{nu}{sub l} and {xi}{sub b}{sup 0}{yields}{xi}{sub c}{sup +}l{sup -}{nu}{sub l} (l=e,{mu}). We work on coordinate space, with baryon wave functions recently obtained from a variational approach based on heavy quark symmetry. We develop a novel expansion of the electroweak current operator, which supplemented with heavy quark effective theory constraints, allows us to predict the baryon form factors and the decay distributions for all q{sup 2} (or equivalently w) values accessible in the physical decays. Our results for the partially integrated longitudinal and transverse decay widths, in the vicinity of the w=1 point, are in excellent agreement with lattice calculations. Comparison of our integrated {lambda}{sub b}-decay width to experiment allows us to extract the V{sub cb} Cabbibo-Kobayashi-Maskawa matrix element for which we obtain a value of |V{sub cb}|=0.040{+-}0.005(stat){sub -0.002}{sup +0.001}(theory) also in excellent agreement with a recent determination by the DELPHI Collaboration from the exclusive B{sub d}{sup 0}{yields}D*{sup +}l{sup -}{nu}{sub l} decay. Besides for the {lambda}{sub b}({xi}{sub b})-decay, the longitudinal and transverse asymmetries and the longitudinal to transverse decay ratio are =-0.954{+-}0.001(-0.945{+-}0.002), =-0.665{+-}0.002(-0.628{+-}0.004), and R{sub L/T}=1.63{+-}0.02(1.53{+-}0.04), respectively.

Relativistic effects in two-particle emission for electron and neutrino reactions

Two-particle two-hole contributions to electroweak response functions are computed in a fully relativistic Fermi gas, assuming that the electroweak current matrix elements are independent of the kinematics. We analyze the genuine kinematical and relativistic effects before including a realistic meson-exchange current (MEC) operator. This allows one to study the mathematical properties of the non-trivial seven-dimensional integrals appearing in the calculation and to design an optimal numerical procedure to reduce the computation time. This is required for practical applications to CC neutrino scattering experiments, where an additional integral over the neutrino flux is performed. Finally we examine the viability of this model to compute the electroweak 2p-2h response functions.

Pionic decay of Λ hypernuclei in a continuum shell model

We evaluate pionic decay widths of \ensuremath{\Lambda} hypernuclei using a shell model for both the nuclear bound and continuum nucleon wave functions in the final state and distorted waves for the outgoing pion. An excellent agreement with the recent KEK measurement of

Angular distribution in two-particle emission induced by neutrinos and electrons

{\ensuremath{\pi}}^{\ensuremath{-}}

Exclusive

-decay widths of