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J. Nieves

Publications and source records attributed to J. Nieves.

At least 181 records · Page 10Linked to original sources
arXiv2006

Study of exclusive semileptonic and nonleptonic decays of $B_c^-$ in a nonrelativistic quark model

We present results for different observables measured in semileptonic and non-leptonic decays of the $B_c^-$ meson. The calculations have been done within the framework of a nonrelativistic constituent quark model. In order to check the sensitivity of all our results against the inter-quark interaction we use five different quark--quark potentials. We obtain form factors, decay widths and asymmetry parameters for semileptonic $B_c^-\to c\bar c$ and $B_c^-\to \bar B$ decays. In the limit of infinite heavy quark mass our model reproduces the constraints of heavy quark spin symmetry. For the actual heavy quark masses we find nonetheless large corrections to that limiting situation for some form factors. We also analyze exclusive non-leptonic two--meson decay channels within the factorization approximation.

hep-ph↗
arXiv2006

Large $N$ Weinberg-Tomozawa interaction and spin-flavor symmetry

The construction of an extended version of the Weinberg-Tomozawa Lagrangian, in which baryons and mesons form spin-flavor multiplets, is reviewed and some of its properties discussed, for an arbitrary number of colors and flavors. The coefficient tables of spin-flavor irreducible representations related by crossing between the $s$-, $t$- and $u$-channels are explicitly constructed.

hep-ph↗
arXiv2006

Doubly heavy quark baryon spectroscopy and semileptonic decay

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.

hep-ph↗
arXiv2006

Study of semileptonic and nonleptonic decays of the $B_c^-$ meson

We evaluate semileptonic and two--meson nonleptonic decays of the $B_c^-$ meson in the framework of a nonrelativistic quark model. The former are done in spectator approximation using one--body current operators at the quark level. Our model reproduces the constraints of heavy quark spin symmetry obtained in the limit of infinite heavy quark mass. For the two--meson nonleptonic decays we work in factorization approximation. We compare our results to the ones obtained in different relativistic approaches.

hep-ph↗
arXiv2006

Study of the semileptonic decays B->pi, D->pi and D->K

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.

hep-ph↗
arXiv2006

Strong one-pion decay of $Σ_c$, $Σ_c^*$ and $Ξ_c^*$

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.

hep-ph↗
arXiv2006

Large Nc Weinberg-Tomozawa interaction and negative parity s--wave baryon resonances

It is shown that in the 70 and 700 SU(6) irreducible spaces, the SU(6) extension of the Weinberg-Tomozawa (WT) s-wave meson-baryon interaction incorporating vector mesons ({\it hep-ph/0505233}) scales as ${\cal O}(N_c^0)$, instead of the well known ${\cal O}(N_c^{-1})$ behavior for its SU(3) counterpart. However, the WT interaction behaves as order ${\cal O}(N_c^{-1})$ within the 56 and 1134 meson-baryon spaces. Explicit expressions for the WT couplings (eigenvalues) in the irreducible SU(2$N_F$) spaces, for arbitrary $N_F$ and $N_c$, are given. This extended interaction is used as a kernel of the Bethe-Salpeter equation, to study the large $N_c$ scaling of masses and widths of the lowest--lying negative parity s-wave baryon resonances. Analytical expressions are found in the $N_c\to \infty$ limit, from which it can be deduced that resonance widths and excitation energies $(M_R-M)$ behave as order ${\cal O} (N^0_c)$, in agreement with model independent arguments, and moreover they fall in the 70-plet, as expected in constituent quark models for an orbital excitation. For the 56 and 1134 spaces, excitation energies and widths grow ${\cal O} (N_c^{1/2})$ indicating that such resonances do not survive in the large $N_c$ limit. The relation of this latter $N_c$ behavior with the existence of exotic components in these resonances is discussed. The interaction comes out repulsive in the 700.

hep-ph↗
arXiv2006

Nuclear effects on lepton polarization in charged-current quasielastic neutrino scattering

We use a correlated local Fermi gas (LFG) model, which accounts also for long distance corrections of the RPA type and final-state interactions, to compute the polarization of the final lepton in charged-current quasielastic neutrino scattering. The present model has been successfully used in recent studies of inclusive neutrino nucleus processes and muon capture. We investigate the relevance of nuclear effects in the particular case of $τ$ polarization in tau-neutrino induced reactions for several kinematics of relevance for neutrino oscillation experiments.

nucl-th↗
arXiv2006

Charged and Neutral Current Neutrino Induced Nucleon Emission Reactions

By means of a Monte Carlo cascade method, to account for the rescattering of the outgoing nucleon, we study the charged and neutral current inclusive one nucleon knockout reactions off nuclei induced by neutrinos. The nucleon emission process studied here is a clear signal for neutral--current neutrino driven reactions, and can be used in the analysis of future neutrino experiments.

hep-ph↗
arXiv2006

Theoretical uncertainties on quasielastic charged-current neutrino-nucleus cross sections

We estimate the theoretical uncertainties of the model developed in Phys. Rev. C70 055503 for inclusive quasielastic charged-current neutrino-nucleus reactions at intermediate energies. Besides we quantify the deviations of the predictions of this many body framework from those obtained within a simple Fermi gas model. An special attention has been paid to the ratio σ(μ)/σ(e) of interest for experiments on atmospheric neutrinos. We show that uncertainties affecting this ratio are likely smaller than 5%

hep-ph↗
arXiv2006

SU(6) Extension of the Weinberg-Tomozawa Meson-Baryon Lagrangian

A consistent SU(6) extension of the Weinberg-Tomozawa meson-baryon chiral Lagrangian is constructed which incorporates vector meson and baryon decuplet degrees of freedom. The corresponding Bethe-Salpeter approximation predicts the existence of an isoscalar spin-parity ${3/2}^-$ $K^*N$ bound state (strangeness +1) with a mass around 1.7--1.8$ $GeV. It is the highest hypercharge state of an antidecuplet SU(3) representation and it is unstable through $K^*$ decay. The estimated width of this state (neglecting d-wave $KN$ decay) turns out to be small ($Γ\le 15 $MeV). Clear signals of this resonance would be found in reactions like $γp \to {\bar K}^0 p K^+ π^-$ by looking at the three body $p K^+ π^-$ invariant mass.

hep-ph↗
arXiv2006

Inclusive Nucleon Emission Induced by Quasi--Elastic Neutrino--Nucleus Interactions

We study the quasi--elastic contribution to the inclusive $(ν_l,ν_l N)$, $(ν_l,l^- N)$, $({\bar ν}_l,{\bar ν}_l N)$ and $({\bar ν}_l,l^+ N)$ reactions in nuclei using a Monte Carlo simulation method to account for the rescattering of the outgoing nucleon. As input, we take the reaction probability from the microscopical many body framework developed in Phys. Rev. {\bf C70} (2004) 055503 for charged-current induced reactions, while for neutral currents we use results from a natural extension of the model described in that reference. The nucleon emission process studied here is a clear signal for neutral--current neutrino driven reactions, that can be used in the analysis of future neutrino experiments.

hep-ph↗
arXiv2006

Quasi-Elastic Neutrino-Nucleus Reactions

The quasi-elastic contribution of the nuclear inclusive electron scattering model developed in A. Gil, J. Nieves, and E. Oset: Nucl. Phys. A 627 (1997) 543; is extended to the study of electroweak Charged Current (CC) induced nuclear reactions at intermediate energies of interest for future neutrino oscillation experiments. The model accounts for long range nuclear (RPA) correlations, Final State Interaction and Coulomb corrections. RPA correlations are shown to play a crucial role in the whole range of neutrino energies, up to 500 MeV, studied in this work. Predictions for inclusive muon capture for different nuclei, and for the reactions $^{12}$C$(ν_μ,μ^-)X$ and $^{12}$C$(ν_e,e^-)X$ near threshold are also given.

hep-ph↗
arXiv2005

Strong one-pion decay of ground state charmed baryons

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.

hep-ph↗
arXiv2005

Study of the strong $Σ_c\to Λ_c π$, $Σ_c^{*}\to Λ_c π$ and $Ξ_c^{*}\to Ξ_c π$ decays in a nonrelativistic quark model

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.

hep-ph↗
arXiv2005

Semileptonic $B\to π$ Decays from an Omnès Improved Nonrelativistic Constituent Quark Model

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.

hep-ph↗