arXiv subjects
Publications and source records attributed to C. Albertus.
Heavy quark spin symmetry is discussed in the context of single and doubly heavy baryons. A special attention is paid to the constraints/simplifications that this symmetry imposes on the non-relativistic constituent quark model wave functions and on the b->c semileptonic decays of these hadrons.
We analyze the effects of hyperfine mixing in $b\to c\, $ semileptonic and electromagnetic decays of doubly heavy baryons.
We investigate the role of hyperfine mixing in the electromagnetic decay of ground state doubly heavy $bc$ baryons. As in the case of a previous calculation on $b\to c$ semileptonic decays of doubly heavy baryons, we find large corrections to the electromagnetic decay widths due to this mixing. Contrary to the weak case just mentioned, we find here that one can not use electromagnetic width relations obtained in the infinite heavy quark mass limit to experimentally extract information on the admixtures in a model independent way.
We analyze the effects of hyperfine mixing in $b \to c$ semileptonic decays of doubly heavy baryons. We qualitatively confirm the results by W. Roberts and M. Pervin in Int. J. Mod. Phys. A, 2009, {\bf 24}: 2401-2413, finding that mixing has a great impact on those transitions. However, predictions without mixing differ by a factor of 2 and this discrepancy translates to the mixed case where large differences in decay widths are observed between the two calculations.
We qualitatively corroborate the results of W. Roberts and M. Pervin in Int. J. Mod. Phys. A 24, 2401 (2009) according to which hyperfine mixing greatly affects the decay widths of $b\to c$ semileptonic decays involving doubly heavy $bc$ baryons. However, our predictions for the decay widths of the unmixed states differ from those reported in the work of Roberts and Pervin by a factor of 2, and this discrepancy translates to the mixed case. We further show that the predictions of heavy quark spin symmetry, might be used in the future to experimentally extract information on the admixtures in the actual physical $bc$ baryons, in a model independent manner.
We evaluate static properties and semileptonic decays for the ground state of doubly heavy $Ξ, Ξ', Ξ^*$ and $Ω, Ω', Ω^*$ baryons. Working in the framework of a nonrelativistic quark model, we solve the three--body problem by means of a variational ansazt made possible by heavy quark spin symmetry constraints. To check the dependence of our results on the inter-quark interaction we use five different quark-quark potentials that include a confining term plus Coulomb and hyperfine terms coming from one--gluon exchange. Our results for static properties (masses, charge and mass radii, magnetic moments...) are, with a few exceptions for the magnetic moments, in good agreement with a previous Faddeev calculation. Our much simpler wave functions are used to evaluate semileptonic decays of doubly heavy $Ξ,Ξ'(J=1/2)$ and $Ω, Ω'(J=1/2)$ baryons. Our results for the decay widths are in good agreement with calculations done within a relativistic quark model in the quark--diquark approximation.
We evaluate masses and semileptonic decay widths for the ground state of doubly heavy $Ξ$ and $Ω$ baryons in the framework of a nonrelativistic quark model. We solve the three-body problem by means of a variational ansatz made possible by heavy-quark spin symmetry constraints. Our masses are comparable to the ones obtained in relativistic calculations and we get one of the best agreements with lattice data. Our simple wave functions are used to evaluate semileptonic decays of doubly heavy $Ξ, Ξ'(J=1/2)$ and $Ω, Ω'(J=1/2)$ baryons. Our results for the decay widths are in reasonable agreement with calculations done in a relativistic calculation in the quark-diquark approximation. We also check that our wave functions comply with what it is expected in the infinite heavy quark mass limit.
The semileptonic decay B->pi is studied starting from a simple quark model and taking into account the effect of the B* resonance. A novel, multiply subtracted, Omnès dispersion relation has been implemented to extend the predictions of the quark model to all physical q^2 values. We find |V_{ub}|=0.0034 +/- 0.0003(exp.)+/- 0.0007(theory), in good agreement with experiment.
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 resultson the inter-quark interaction we have used five different quarkquark potentials which include Coulomb and hyperfine terms coming fromone-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 a good agreement with the ones obtained within a relativistic quark model in the quark-diquark approximation.
The semileptonic decay B->pi is studied starting from a simple quark model that takes into account the effect of the B* resonance. A novel, multiply subtracted, Omnes dispersion relation has been implemented to extend the predictions of the quark model to all q^2 values accesible in the physical decay. By comparison to the experimental data, we extract |V_ub|=0.0034 +/- 0.0003(exp.) +/- 0.0007(theory). As a further test of the model, we have also studied D->pi and D->K decays for which we get good agreement with experiment.
Working in the framework of a nonrelativistic quark model we evaluate the widths for the strong one-pion decays $Σ_c\toΛ_c π$, $Σ_c^*\toΛ_c π$ and $Ξ_c^{*}\toΞ_c π$. We take advantage of the constraints imposed by heavy quark symmetry to solve the three-body problem by means of a simple variational ansatz. We use partial conservation of the axial current hypothesis to get the strong vertices from weak axial current matrix elements. Our results are in good agreement with experimental data.
We evaluate the widths for the strong decays $Σ_c\toΛ_c π$, $Σ_c^*\toΛ_c π$ and $Ξ_c^{*}\toΞ_c π$. The calculations have been done within a nonrelativistic constituent quark model with wave functions that take advantage of the constraints imposed by heavy quark symmetry. Partial conservation of axial current hypothesis allows us to determine the strong vertices from an analysis of the weak axial current matrix elements. Our results are in good agreement with experimental data.
We present results for the strong widths corresponding to the $Σ_c\to Λ_c π$, $Σ_c^{*}\to Λ_c π$ and $Ξ_c^{*}\to Ξ_c π$ decays. The calculations have been done in a nonrelativistic constituent quark model with wave functions that take advantage of the constraints imposed by heavy quark symmetry. Partial conservation of axial current hypothesis allows us to determine the strong vertices from an analysis of the axial current matrix elements. Our results \hbox{$Γ(Σ_c^{++}\to Λ_c^+ π^+)=2.41 \pm0.07\pm0.02 \mathrm{MeV}$}, {$Γ(Σ_c^{+}\to Λ_c^+ π^0)=2.79 \pm0.08\pm0.02 \mathrm{MeV}$}, {$Γ(Σ_c^{0}\to Λ_c^+ π^-)=2.37 \pm0.07\pm0.02 \mathrm{MeV}$}, {$Γ(Σ_c^{* ++}\to Λ_c^+ π^+)=17.52\pm0.74\pm0.12 \mathrm{MeV}$}, {$Γ(Σ_c^{* +}\to Λ_c^+ π^0)=17.31\pm0.73\pm0.12 \mathrm{MeV}$}, {$Γ(Σ_c^{* 0}\to Λ_c^+ π^-)=16.90\pm0.71\pm0.12 \mathrm{MeV}$}, {$Γ(Ξ_c^{* +}\to Ξ_c^0 π^++Ξ_c^+π^0)=3.18\pm0.10\pm0.01 \mathrm{MeV}$} and {$Γ(Ξ_c^{* 0}\to Ξ_c^+ π^-+Ξ_c^0π^0)=3.03\pm0.10\pm0.01 \mathrm{MeV}$} are in good agreement with experimental determinations.
The semileptonic $B\to πl^+ ν_l$ 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 $q^2_{\rm max}=(m_B-m_π)^2$ to all $q^2$ values accessible in the physical decay, we use a novel multiply-subtracted Omnès dispersion relation, which considerably diminishes the form factor dependence on the elastic $πB \to πB$ scattering amplitudes at high energies. By comparison to the experimental branching fraction we extract $|V_{ub}| = 0.0034 \pm 0.0003 ({\rm exp}) \pm 0.0007 ({\rm theory})$. To further test our framework, we also study $D\to π$ and $D\to K$ decays and find excellent results $\frac{f^+_π(0)}{f^+_K(0)} = 0.80 \pm 0.03, \quad \frac{{\cal B}(D^0\to π^- e^+ ν_e)}{{\cal B}(D^0\to K^- e^+ ν_e)}= 0.079 \pm 0.008$. In particular for the $D\to π$ case, we reproduce, with high accuracy, the three-flavor lattice QCD results recently obtained by the Fermilab-MILC-HPQCD Collaboration. While for the $D\to K$ case, we successfully describe the data for $f^+(q^2)/f^+(0)$ recently measured by the FOCUS Collaboration.
We present results for different observables in weak decays of pseudoscalar and vector mesons with a heavy $c$ or $b$ quark. The calculations are done in a nonrelativistic constituent quark model improved at some instances by heavy quark effective theory constraints. We determine pseudoscalar and vector meson decay constants that within a few per cent satisfy $f_V M_V/f_P M_P=1$, a result expected in heavy quark symmetry when the heavy quark masses tend to infinity. We also analyze the semileptonic $B\to D$ and $B\to D^*$ decays for which we evaluate the different form factors. Here we impose heavy quark effective theory constraints among form factors that are not satisfied by a direct quark model calculation. The value of the form factors at zero recoil allows us to determine, by comparison with experimental data, the value of the $|V_{cb}|$ Cabbibo-Kobayashi-Maskawa matrix element. From the $B\to D$ semileptonic decay we get $|V_{cb}|=0.040\pm0.006$ in perfect agreement with our previous determination based on the study of the semileptonic $Λ_b\to Λ_c$ decay and also in excellent agreement with a recent experimental determination by the DELPHI Collaboration. We further make use of the partial conservation of axial current hypothesis to determine the strong coupling constants $g_{B^*Bπ}(0)=60.5\pm 1.1$ and $g_{D^*Dπ}(0)=22.1\pm0.4$. The ratio $R=(g_{B^*Bπ}(0) f_{B^*}\sqrt{M_D})/ (g_{D^*Dπ}(0) f_{D^*}\sqrt{M_B})=1.105\pm0.005$ agrees with the heavy quark symmetry prediction of 1.
We evaluate different properties of baryons with a heavy c or b quark. The use of Heavy Quark Symmetry (HQS) provides with an important simplification of the non relativistic three body problem which can be solved by means of a simple variational approach. This scheme is able to reproduce previous results obtained with more involved Faddeev calculations. The resulting wave functions are parametrized in a simple manner, and can be used to calculate further observables.
We present the results of a nonrelativistic constituent quark model study of the semileptonic decays $Λ_b^0 \to Λ_c^+ l^- {\bar ν}_l$ and $Ξ_b^0 \to Ξ_c^+ l^- {\bar ν}_l$. 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 $q^2$ (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 $Λ_b-$decay width to experiment allows us to extract the $V_{cb}$ Cabbibo-Kobayashi-Maskawa matrix element for which we obtain a value of $|V_{cb}| = 0.040\pm 0.005 ({\rm stat}) ^{+0.001}_{-0.002} ({\rm theory})$ also in excellent agreement with a recent determination by the DELPHI Collaboration from the exclusive ${\bar {\rm B}^0_{\rm d}} \to {\rm D}^{*+}l^-{\bar ν}_l$ decay. Besides for the $Λ_b (Ξ_b)-$decay, the longitudinal and transverse asymmetries, and the longitudinal to transverse decay ratio are $ =-0.954\pm 0.001 (-0.945\pm 0.002)$, $ =-0.665\pm 0.002 (-0.628\pm 0.004)$ and $R_{L/T}=1.63\pm 0.02 (1.53\pm 0.04)$, respectively.
Within the framework of a nonrelativistic quark model we evaluate the six form factors associated to the Λ_b^0 \to Λ_c^+ l^- \barν_l semileptonic decay. The baryon wave functions were evaluated using a variational approach applied to a family of trial functions constrained by Heavy Quark Symmetry (HQS). We use a spectator model with only one-body current operators. For these operators we keep up to first order terms on the internal (small) heavy quark momentum, but all orders on the transferred (large) momentum. Our result for the partially integrated decay width is in good agreement with lattice calculations. Comparison of our total decay width to experiment allows us to extract the V_{cb} Cabbibo-Kobayashi-Maskawa matrix element for which we obtain a value of |V_{cb}|=0.047\pm 0.005 in agreement with a recent determination by the DELPHI Collaboration. Furthermore, we obtain the universal Isgur-Wise function with a slope parameter ρ^2=0.98 in agreement with lattice results.