Search

We have developed a model for neutrino-induced coherent pion production off nuclei in the energy regime of interest for present and forthcoming neutrino oscillation experiments. It is based on a microscopic model for pion production off the nucleon that, besides the dominant Delta pole contribution, takes into account the effect of background terms required by chiral symmetry. Moreover, the model uses a reduced nucleon-to-Delta resonance axial coupling, which leads to coherent pion production cross sections around a factor two smaller than most of the previous theoretical estimates. In the coherent production, the main nuclear effects, namely medium corrections on the Delta propagator and the final pion distortion, are included. We have improved on previous similar models by taking into account the nucleon motion and employing a more sophisticated optical potential. As found in previous calculations the modification of the Delta self-energy inside the nuclear medium strongly reduces the cross section, while the final pion distortion mainly shifts the peak position to lower pion energies. The angular distribution profiles are not much affected by nuclear effects. Nucleon motion increases the cross section by 15% at neutrino energies of 650 MeV, while Coulomb effects on charged pions are estimated to be small. Finally, we discuss at length the deficiencies of the Rein-Sehgal pion coherent production model for neutrino energies below 2 GeV, and in particular for the MiniBooNE and T2K experiments. We also predict flux averaged cross sections for these two latter experiments and K2K., Comment: 19 latex pages, 10 figures, 2 tables. Minor changes. Version accepted for publication in Physical Review D

We review Quasielastic (QE) inclusive and semi--inclusive neutrino/antineutrino Charged Current (CC) and Neutral Current (NC) induced nuclear reactions at intermediate energies. We pay special attention to nuclear corrections besides Pauli blocking: Long and Short range nuclear correlations (RPA and SRC) and particle and hole Spectral Functions (SF). We also critically review the use of the Plane and Distorted Wave Impulse approximations (PWIA and DWIA) to describe inclusive one nucleon knockout reactions off nuclei. In this context, we present results from a Monte Carlo cascade method to account for the rescattering of the outgoing nucleon. Finally, we examine the effects of chiral non-resonant terms in neutrino pion production off the nucleon, and present some preliminary results on nuclear coherent pion production induced by neutrinos., Comment: Talk given at 10th International Workshop on Neutrino Factories, Super beams and Beta beams, June 30 - July 5 2008, Valencia, Spain

We study charmed baryon resonances which are generated dynamically within a unitary meson-baryon coupled channel model that treats the heavy pseudoscalar and vector mesons on equal footing as required by heavy-quark symmetry. It is an extension of recent SU(4) models with t-channel vector meson exchanges to a SU(8) spin-flavor scheme, but differs considerably from the SU(4) approach in how the strong breaking of the flavor symmetry is implemented. Some of our dynamically generated states can be readily assigned to recently observed baryon resonances, while others do not have a straightforward identification and require the compilation of more data as well as an extension of the model to d-wave meson-baryon interactions and p-wave coupling in the neglected s- and u-channel diagrams. Of several novelties, we find that the Lambda_c(2595), which emerged as a ND quasi-bound state within the SU(4) approaches, becomes predominantly a ND* quasi-bound state in the present SU(8) scheme., Comment: 37 pages, 7 figures. Some parameters of the model have been changed, more channels are considered. To appear in PRD

We check a commonly used approximation in which a baryon with a heavy quark is described as a heavy quark-light diquark system. The heavy quark influences the diquark internal motion reducing the average distance between the two light quarks. Besides, we show how the average distance between the heavy quark and any of the light quarks, and that between the heavy quark and the center of mass of the light diquark, are smaller than the distance between the two light quarks, which seems to contradict the heavy quark-light diquark picture. This latter result is in agreement with expectations from QCD sum rules and lattice QCD calculations. Our results also show that the diquark approximations produces larger masses than the ones obtained in a full calculation., Comment: 9 latex pages, 5 figures, 6 tables

We study neutrino induced one-pion production off the nucleon in and around the Delta resonance region. Apart from the Delta-pole mechanism we include background terms required by chiral symmetry. These background terms give sizeable contributions in all channels. To better reproduce the ANL $q^2$-differential cross section data, we make a new fit of the $C_5^A(q^2)$ axial nucleon to Delta form factor. The new result $C_5^A(0)=0.867\pm 0.075$ is some 30% smaller than the commonly accepted value. This correction is compatible with most quark model estimates and a recent lattice calculation, Comment: 4 latex pages, 2 figures. Contribution at Chiral Symmetry in Hadron and Nuclear Physics (CHIRAL07), Osaka, November 13-16, 2007

Consistent SU(6) and SU(8) spin-flavor extensions of the SU(3) flavor Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian are constructed, which incorporate vector meson degrees of freedom. In the charmless sector, the on-shell approximation to the Bethe-Salpeter (BS) approach successfully reproduces previous SU(3) WT results for the lowest-lying s--wave negative parity baryon resonances. It also provides some information on the dynamics of heavier ones and of the lightest d-wave negative parity resonances, as e.g. the Lambda(1520). For charmed baryons the scheme is consistent with heavy quark symmetry, and our preliminary results in the strangeness-less charm C=+1 sector describe the main features of the three-star J^P=1/2^- Lambda_c(2595) and J^P=3/2^- Lambda_c(2625) resonances. We also find a second broad J^P=1/2^- state close to the Lambda_c(2595), Comment: Presented at Chiral07: Chiral Symmetry in Hadron and Nuclear Physics November 13-16, 2007, Osaka University, Japan

We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon pole, pion and contact terms is calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account., Comment: Contribution to the proceedings of Chiral07, RCNP, Osaka, Japan. Corrected version because of problems on some pdf viewers

We discuss the relevance of nuclear medium effects in the analysis of some low and medium energy neutrino reactions of current interest. In particular, we study the Quasi-Elastic (QE) process, where RPA correlations and Final State Interactions (FSI) are shown to play a crucial role. We have also investigated the neutrino induced coherent pion production. We find a strong reduction of the cross section due to the distortion of the pion wave function and the modification of the production mechanisms in the nucleus. The sensitivity of the results to the axial $N\Delta$ coupling $C_5^A(0)$ has been also investigated., Comment: To appear in the proceedings of Chiral Symmetry in Hadron and Nuclear Physics (Chiral07), Osaka, Japan, November 13-16, 2007

Omnes dispersion relations make a connection between form factors for exclusive semileptonic decays and phase shifts in the corresponding elastic scattering channels. We describe two applications. In the first, we use lattice form factor calculations to learn about phase shifts in elastic s-wave isospin-1/2 channels for K pi, B pi, D pi and D K scattering. The aim of the second application is to make the determination of the CKM matrix element magnitude |Vub| from exclusive semileptonic B to pi decays competitive with that from inclusive decays. Here we use many subtractions in an Omnes dispersion relation to motivate a simple fitting function, allowing data to constrain the q^2 shape of the differential decay rate and theory, primarily lattice results, to provide normalisation via form factor values., Comment: 7 pages, 3 figures, LaTeX

The Quasi-Elastic (QE) contribution of the nuclear inclusive electron model developed in Nucl. Phys. A627 543 (1997) is extended to the study of neutrino/antineutrino Charged Current (CC) and Neutral Current (NC) induced nuclear reactions at intermediate energies. Long range nuclear (RPA) correlations, Final State Interaction (FSI) and Coulomb corrections are included within the model. RPA correlations are shown to play a crucial role in the whole range (100--500 MeV) of studied neutrino energies. Results for inclusive muon capture for different nuclei through the Periodic Table are also discussed. In addition, and by means of a Monte Carlo cascade method to account for the rescattering of the outgoing nucleon, we also study the CC and NC inclusive one nucleon knockout reactions off nuclei., Comment: To appear in the proceedings of 9th International Workshop On Neutrino Factories, Superbeams and Betabeams (NuFact07) August 6-11, 2007, Okayama University, Japan

The neutrino pion production off the nucleon is traditionally described in the literature by means of the weak excitation of the Delta(1232) resonance and its subsequent decay into N pi. Here, we present results from a model that includes also some background terms required by chiral symmetry. We show that the contribution of these terms is sizeable and leads to significant effects in total and partially integrated pion production cross sections at intermediate energies of interest for neutrino oscillation experiments. Finally, we discuss parity-violating contributions to the pion angular differential cross section induced by the interference of these non-resonant terms with the Delta piece., Comment: To appear in the proceedings of 9th International Workshop On Neutrino Factories, Superbeams and Betabeams (NuFact07) August 6-11, 2007, Okayama University, Japan

We study the threshold production of two pions induced by neutrinos in nucleon targets. The contribution of nucleon, pion and contact terms are calculated using a chiral Lagrangian. The contribution of the Roper resonance, neglected in earlier studies, has also been taken into account. The numerical results for the cross sections are presented and compared with the available experimental data. It has been found that in the two pion channels with $\pi^+\pi^-$ and $\pi^0\pi^0$ in the final state, the contribution of the $N^*(1440)$ is quite important and could be used to determine the $N^*(1440)$ electroweak transition form factors if experimental data with better statistics become available in the future., Comment: This version corrects a mistake on the helicity amplitudes sign. Additional comments on resonance-background relative sign are added. Other minor corrections. Matches published version. 17 pages, 7 figures

We show how heavy quark symmetry constraints on doubly heavy baryon semileptonic decay widths can be used to test the validity of different quark model calculations. The large discrepancies in the results observed between different quark model approaches can be understood in terms of a severe violation of heavy quark spin symmetry constraints by some of those models., Comment: 10 LaTex pages, 3 figures, 6 tables. Corrected and enlarged version

We construct a model for the weak pion production off the nucleon, which in addition to the weak excitation of the $\Delta(1232)$ resonance and its subsequent decay into $N\pi$, it includes also some background terms required by chiral symmetry. We re-fit the $C_5^A(q^2)$ form factor to the flux averaged $\nu_\mu p \to \mu^-p\pi^+$ ANL $q^2-$differential cross section data, finding a substantially smaller contribution of the $\Delta$ pole mechanism than traditionally assumed in the literature. We also show that the interference between the Delta pole and the background terms produces parity-violating contributions to the pion angular differential cross section., Comment: To appear in the proceedings of Fifth International Workshop on. Neutrino-Nucleus Interactions in the Few-GeV Region. May 30, 2007 - June 3, 2007. Fermilab, Batavia, Illinois USA

We evaluate masses and semileptonic decay widths for the ground state of doubly heavy $\Xi$ and $\Omega$ 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 $\Xi, \Xi'(J=1/2)$ and $\Omega, \Omega'(J=1/2)$ 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., Comment: 3 latex pages, two tables. To appear in the INPC07 proceedings

We develop a model for the weak pion production off the nucleon, which besides the Delta pole mechanism (weak excitation of the $\Delta(1232)$ resonance and its subsequent decay into $N\pi$), includes also some background terms required by chiral symmetry. We re-fit the $C_5^A(q^2)$ form factor to the flux averaged $\nu_\mu p \to \mu^-p\pi^+$ ANL $q^2-$differential cross section data, finding a substantially smaller contribution of the Delta pole mechanism than traditionally assumed in the literature. Within this scheme, we calculate several differential and integrated cross sections, including pion angular distributions, induced by neutrinos and antineutrinos and driven both by charged and neutral currents. In all cases we find that the background terms produce quite significant effects and that they lead to an overall improved description of the data, as compared to the case where only the Delta pole mechanism is considered. We also show that the interference between the Delta pole and the background terms produces parity-violating contributions to the pion angular differential cross section, which are intimately linked to $T-$odd correlations in the contraction between the leptonic and hadronic tensors. However, these latter correlations do not imply a genuine violation of time reversal invariance because of the existence of strong final state interaction effects., Comment: Typos corrected; comments added

Starting from a consistent SU(6) extension of the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian (Phys. Rev. D74 (2006) 034025), we study the s-wave meson-baryon resonances in the strangeness S=-3 and negative parity sector. Those resonances are generated by solving the Bethe-Salpeter equation with the WT interaction used as kernel. The considered mesons are those of the 35-SU(6)-plet, which includes the pseudoscalar (PS) octet of pions and the vector (V) nonet of the rho meson. For baryons we consider the 56-SU(6)-plet, made of the 1/2+ octet of the nucleon and the 3/2+ decuplet of the Delta. Quantum numbers I(J^P)=0(3/2^-) are suggested for the experimental resonances Omega*(2250)- and Omega*(2380)-. Among other, resonances with I=1 are found, with minimal quark content sss\bar{l}l', being s the strange quark and l, l' any of the the light up or down quarks. A clear signal for such a pentaquark would be a baryonic resonance with strangeness -3 and electric charge of -2 or 0, in proton charge units. We suggest looking for K- Xi- resonances with masses around 2100 and 2240 MeV in the sector 1(1/2^-), and for pi Omega- and K- Xi*- resonances with masses around 2260 MeV in the sector 1(3/2^-)., Comment: 3 pages, 1 Postscript figure, 7 tables

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, Omn\`es 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., Comment: Three pages, two figures. To appear in the proceedings of Quark Confinament and Hadron Spectrum VII. Azores, September 2006

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., Comment: 3 pages, no figures. Presented at the IVth International Conference on Quarks and Nuclear Physics, Madrid, June 5th-10th 2006

Vector meson degrees of freedom are incorporated into the Weinberg-Tomozawa (WT) meson-baryon chiral Lagrangian by using a scheme which relies on spin--flavor SU(6) symmetry. The corresponding Bethe-Salpeter approximation successfully reproduces previous SU(3)--flavor WT results for the lowest-lying s--wave negative parity baryon resonances, and it also provides some information on the dynamics of the heavier ones. Moreover, it also predicts the existence of an isoscalar spin-parity $\frac32^-$ $K^*N$ bound state (strangeness +1) with a mass around 1.7--1.8 GeV, unstable through $K^*$ decay. Neglecting d-wave KN decays, this state turns out to be quite narrow ($\Gamma \le 15$ MeV) and it might provide clear signals in reactions like $\gamma p \to \bar K^0 p K^+\pi^-$ by looking at the three body $p K^+\pi^-$ invariant mass., Comment: Talk given at the IVth International Conference on Quarks an Nuclear Physics, Madrid, June 5th-10th 2006. Minor corrections

Working in the framework of a nonrelativistic quark model we evaluate the spectra and semileptonic decay widths for the ground state of doubly heavy $\Xi$ and $\Omega$ 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., Comment: Talk given at the IVth International Conference on Quarks an Nuclear Physics (QNP06), Madrid, June 5th-10th 2006

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., Comment: Talk given at the IVth International Conference on Quarks an Nuclear Physics, Madrid, June 5th-10th 2006

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., Comment: 3 pages, 5 figures. Talk given at the IV International Conference on Quarks and Nuclear Physics (QNP06), Madrid, June 5th - 10th 2006

Working in the framework of a nonrelativistic quark model we evaluate the widths for the strong one-pion decays $\Sigma_c\to\Lambda_c \pi$, $\Sigma_c^*\to\Lambda_c \pi$ and $\Xi_c^{*}\to\Xi_c \pi$. 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., Comment: 3 latex pages. Contribution to the Proceedings of the Quark Confinement and the Hadron Spectrum VII Conference (QCHS7) Ponta Delgada (PT) Sept 2-7, 2006

We evaluate static properties and semileptonic decays for the ground state of doubly heavy $\Xi, \Xi', \Xi^*$ and $\Omega, \Omega', \Omega^*$ 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 $\Xi,\Xi'(J=1/2)$ and $\Omega, \Omega'(J=1/2)$ baryons. Our results for the decay widths are in good agreement with calculations done within a relativistic quark model in the quark--diquark approximation., Comment: 23 latex pages, 7 figures, 11 tables. Corrected version according to the discussion in the erratum to be published in Eur. Phys. J. A. Eur. Phys. J. A 32, 183 (2007); erratum Eur. Phys. J. A in press, available as online first

A potential way to distinguish tau-neutrinos from antineutrinos, below the tau-production threshold, but above the pion production one, is presented. It is based on the different behavior of the neutral current pion production off the nucleon, depending on whether it is induced by neutrinos or antineutrinos. This procedure for distinguishing tau-neutrinos from antineutrinos neither relies on any nuclear model, nor it is affected by any nuclear effect (distortion of the outgoing nucleon waves, etc...). We show that neutrino-antineutrino asymmetries occur both in the totally integrated cross sections and in the pion azimuthal differential distributions. To define the asymmetries for the latter distributions we just rely on Lorentz-invariance. All these asymmetries are independent of the lepton family and can be experimentally measured by using electron or muon neutrinos, due to the lepton family universality of the neutral current neutrino interaction. Nevertheless and to estimate their size, we have also used the chiral model of hep-ph/0701149 at intermediate energies. Results are really significant since the differences between neutrino and antineutrino induced reactions are always large in all physical channels., Comment: Revised version. 8 pages, 3 figures. The abstract has been changed and discussion extended

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., Comment: 41 latex pages, 14 figures, 21 tables.Version accepted for publication in Phys. Rev. D

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 $\tau$ polarization in tau-neutrino induced reactions for several kinematics of relevance for neutrino oscillation experiments., Comment: 13 pages, 8 figures

We compare local Fermi gas and shell model in muon capture in nuclei in order to estimate the effect of finite nuclear size in low energy weak reactions., Comment: 6 pages, 8 figures. To be published in the Proceedings of 20th Max Born Symposium, Wroclaw (Poland), December 7-10, 2005

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., Comment: 5 pages, 4 figures. Contribution to 20th Max Born Symposium, Wroclaw Poland), December 7-10, 2005

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., Comment: 21 pages, 3 figures, requires wick.sty and young.sty. Subsection added. Conclusions revised. To appear in Physical Review D

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 \sigma(\mu)/\sigma(e) of interest for experiments on atmospheric neutrinos. We show that uncertainties affecting this ratio are likely smaller than 5%, Comment: 10 pages, 6 figures. Few errors corrected. Accepted in Physics Letters B

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$(\nu_\mu,\mu^-)X$ and $^{12}$C$(\nu_e,e^-)X$ near threshold are also given., Comment: 8 pages, 5 figures; To appear in the proceedings of Medex'05 Meeting (Corfu, Greece September 2005) (Czech. J. Phys.)

We evaluate the widths for the strong decays $\Sigma_c\to\Lambda_c \pi$, $\Sigma_c^*\to\Lambda_c \pi$ and $\Xi_c^{*}\to\Xi_c \pi$. 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., Comment: 3 latex pages. Contribution to the Proceedings of the Particles and Nuclei International Conference (PANIC05). Santa Fe (NM) Oct 24-28, 2005

We study the quasi--elastic contribution to the inclusive $(\nu_l,\nu_l N)$, $(\nu_l,l^- N)$, $({\bar \nu}_l,{\bar \nu}_l N)$ and $({\bar \nu}_l,l^+ N)$ 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., Comment: 23 pages, 17 figures; Version 2: few typos corrected

We present results for the strong widths corresponding to the $\Sigma_c\to \Lambda_c \pi$, $\Sigma_c^{*}\to \Lambda_c \pi$ and $\Xi_c^{*}\to \Xi_c \pi$ 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{$\Gamma(\Sigma_c^{++}\to \Lambda_c^+ \pi^+)=2.41 \pm0.07\pm0.02 \mathrm{MeV}$}, {$\Gamma(\Sigma_c^{+}\to \Lambda_c^+ \pi^0)=2.79 \pm0.08\pm0.02 \mathrm{MeV}$}, {$\Gamma(\Sigma_c^{0}\to \Lambda_c^+ \pi^-)=2.37 \pm0.07\pm0.02 \mathrm{MeV}$}, {$\Gamma(\Sigma_c^{* ++}\to \Lambda_c^+ \pi^+)=17.52\pm0.74\pm0.12 \mathrm{MeV}$}, {$\Gamma(\Sigma_c^{* +}\to \Lambda_c^+ \pi^0)=17.31\pm0.73\pm0.12 \mathrm{MeV}$}, {$\Gamma(\Sigma_c^{* 0}\to \Lambda_c^+ \pi^-)=16.90\pm0.71\pm0.12 \mathrm{MeV}$}, {$\Gamma(\Xi_c^{* +}\to \Xi_c^0 \pi^++\Xi_c^+\pi^0)=3.18\pm0.10\pm0.01 \mathrm{MeV}$} and {$\Gamma(\Xi_c^{* 0}\to \Xi_c^+ \pi^-+\Xi_c^0\pi^0)=3.03\pm0.10\pm0.01 \mathrm{MeV}$} are in good agreement with experimental determinations., Comment: 8 latex pages. Shortened version accepted for publication in Physical Review D

The semileptonic $B\to \pi l^+ \nu_l$ 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 $q^2_{\rm max}=(m_B-m_\pi)^2$ to all $q^2$ values accessible in the physical decay, we use a novel multiply-subtracted Omn\`es dispersion relation, which considerably diminishes the form factor dependence on the elastic $\pi B \to \pi B$ 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 $D\to \pi$ and $D\to K$ decays and find excellent results $\frac{f^+_\pi(0)}{f^+_K(0)} = 0.80 \pm 0.03, \quad \frac{{\cal B}(D^0\to \pi^- e^+ \nu_e)}{{\cal B}(D^0\to K^- e^+ \nu_e)}= 0.079 \pm 0.008$. In particular for the $D\to \pi$ case, we reproduce, with high accuracy, the three-flavor lattice QCD results recently obtained by the Fermilab-MILC-HPQCD Collaboration. While for the $D\to K$ case, we successfully describe the data for $f^+(q^2)/f^+(0)$ recently measured by the FOCUS Collaboration., Comment: 17 pages, minor modifications. Accepted in PRD

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 ($\Gamma \le 15 $MeV). Clear signals of this resonance would be found in reactions like $\gamma p \to {\bar K}^0 p K^+ \pi^-$ by looking at the three body $p K^+ \pi^-$ invariant mass., Comment: 5 pages, REVTex, 1 Figure, discussion and references added

The Quasi-Elastic contribution of the nuclear inclusive electron scattering model developed in Nucl. Phys. A 627 (1997) 543 is extended to the study of electroweak Charged Current 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$(\nu_\mu,\mu^-)X$ and $^{12}$C$(\nu_e,e^-)X$ near threshold are also given., Comment: 11 pages, 10 figures. To appear in the proceedings of RCCN workshop on "Sub-Dominant Oscillation Effects in Atmospheric Neutrino Experiment"

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 $\Lambda_b\to \Lambda_c$ 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 $g_{B^*B\pi}(0)=60.5\pm 1.1$ and $g_{D^*D\pi}(0)=22.1\pm0.4$. The ratio $R=(g_{B^*B\pi}(0) f_{B^*}\sqrt{M_D})/ (g_{D^*D\pi}(0) f_{D^*}\sqrt{M_B})=1.105\pm0.005$ agrees with the heavy quark symmetry prediction of 1., Comment: 19 Latex pages,6 figures, references added, corrected typos, content enlarged

In this talk I report on selected topics of hadron modification in the nuclear medium using the chiral unitary approach to describe the dynamics of the problems. I shall mention how antikaons, $\eta$, and $\phi$ are modified in the medium and will report upon different experiments done or planned to measure the $\phi$ width in the medium., Comment: 10 pgs, 3 figs. Invited talk in the Workshop on in Medium Hadron Physics, Giessen, Nov 2004

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., Comment: 4 pages. Contribution to the Proceedings of the 10th International Conference on Baryons (Baryons04). Paris, Oct. 25-29, 2004

We present the results of a nonrelativistic constituent quark model study of the semileptonic decays $\Lambda_b^0 \to \Lambda_c^+ l^- {\bar \nu}_l$ and $\Xi_b^0 \to \Xi_c^+ l^- {\bar \nu}_l$. 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 $\Lambda_b-$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 ${\bar {\rm B}^0_{\rm d}} \to {\rm D}^{*+}l^-{\bar \nu}_l$ decay. Besides for the $\Lambda_b (\Xi_b)-$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., Comment: 17 latex pages, 4 figures. Minor changes with respect to the previous version. Accepted for publication in Physical Review D

Motivated by recent studies of inclusive neutrino nucleus processes and muon capture within a correlated local Fermi gas model (LFG), we discuss the relevance of nuclear finite size effects in these reactions at low energy, in particular for muon capture. To disentangle these effects from others coming from the reaction dynamics we employ here a simple uncorrelated shell model that embodies the typical finite size content of the problem. The integrated decay widths of muon atoms calculated with this shell model are then compared for several nuclei with those obtained within the uncorrelated LFG, using in both models exactly the same theoretical ingredients and parameters. We find that the two predictions are in quite good agreement, within 1--7%, when the shell model density and the correct energy balance is used as input in the LFG calculation. The present study indicates that, despite the low excitation energies involved in the reaction, integrated inclusive observables, like the total muon capture width, are quite independent of the fine details of the nuclear wave functions., Comment: 11 pages, 8 figures. Final version to be published in EPJA