arXiv subjects

Juan Nieves

Publications and source records attributed to Juan Nieves.

At least 73 records · Page 4Linked to original sources

arXiv2013

Heavy Quark Symmetries: Molecular Partners of the X(3872) and $Z_{b}(10610)/Z_{b}'(10650)$

In this work, we have used an Effective Field Theory (EFT) framework based on Heavy Quark Spin (HQSS), Heavy Flavour (HFS) and Heavy Antiquark-Diquark symmetries (HADS). Using a standard lagrangian for the heavy meson-heavy antimeson system, we fit the counter-terms of the model to predict some promising experimental data that can be interpreted as heavy meson-heavy antimeson molecules, that is, the X(3872) and the $Z_{b}(10610)/Z'_{b}(10650)$. Next, and, taking advantage of HADS, we use the same lagrangian to explore the consequences for heavy meson-doubly heavy baryon molecules, which can also be interpreted as triply heavy pentaquarks.

hep-ph↗

arXiv2013

Consequences of Heavy Quark Symmetries for Hadronic Molecules

Among the newly observed structures in the heavy quarkonium mass region, some are proposed to be hadronic molecules. We investigate the consequences of heavy quark flavor symmetry on these heavy meson hadronic molecules. The symmetry allows us to predict new hadronic molecules on one hand, and test the hadronic molecular assumption of the observed structures on the other hand. We explore the consequences of the flavor symmetry assuming the X(3872) and $Z_b(10610)$ as a isoscalar $D\bar D^*$ and isovector $B\bar B^*$ hadronic molecule, respectively. A series of hadronic molecules composed of heavy mesons are predicted. In particular, there is an isoscalar $1^{++}$ $B\bar B^*$ bound state with a mass of 10580 MeV which may be searched for in the $Υ(1S,2S)π^+π^-π^0$ mass distribution; the isovector charmonium partners of the $Z_b(10610)$ and the $Z_b(10650)$ are also predicted, one of which probably corresponds to the very recently observed $Z_c(3900)$ and $Z_c(4025)$ resonances by the BESIII Collaboration.

hep-ph↗

arXiv2013

Heavy Antiquark--Diquark Symmetry and Heavy Hadron Molecules: Are There Triply Heavy Pentaquarks?

We explore the consequences of heavy flavour, heavy quark spin and heavy antiquark-diquark symmetries for hadronic molecules within an effective field theory framework.. Owing to heavy antiquark-diquark symmetry, the doubly heavy baryons have approximately the same light-quark structure as the heavy antimesons. As a consequence, the existence of a heavy meson-antimeson molecule implies the possibility of a partner composed of a heavy meson and a doubly-heavy baryon. In this regard, the D\bar D* molecular nature of the X(3872) will hint at the existence of several baryonic partners with isospin I=0 and J^P = 5/2^- or 3/2^-. Moreover, if the Zb(10650) turns out to be a B*\bar B* bound state, we can be confident of the existence of \Xibb* \bar B* hadronic molecules with quantum numbers I(J^P) = 1(1/2^-) and I(J^P) = 1(3/2^-). These states are of special interest since they can be considered to be triply-heavy pentaquarks.

hep-ph↗

arXiv2013

Hidden charm molecules in finite volume

In the present paper we address the interaction of pairs of charmed mesons with hidden charm in a finite box. We use the interaction from a recent model based on heavy quark spin symmetry that predicts molecules of hidden charm in the infinite volume. The energy levels in the box are generated within this model, and from them some synthetic data are generated. These data are then employed to study the inverse problem of getting the energies of the bound states and phase shifts for $D \bar D$ or $D^* {\bar D}^*$. Different strategies are investigated using the lowest two levels for different values of the box size, carrying a study of the errors produced. Starting from the upper level, fits to the synthetic data are carried out to determine the scattering length and effective range plus the binding energy of the ground state. A similar strategy using the effective range formula is considered with a simultaneous fit to the two levels, one above and the other one below threshold. This method turns out to be more efficient than the other one. Finally, a method based on the fit to the data by means of a potential and a loop function conveniently regularized, turns out to be very efficient and allows to produce accurate results in the infinite volume starting from levels of the box with errors far larger than the uncertainties obtained in the final results. A regularization method based on Gaussian wave functions turns out to be rather efficient in the analysis and as a byproduct a practical and fast method to calculate the Lüscher function with high precision is presented.

hep-lat↗

arXiv2013

Heavy-quark spin symmetry for charmed and strange baryon resonances

We study charmed and strange baryon resonances that are generated dynamically by a unitary baryon-meson coupled-channels model which incorporates heavy-quark spin symmetry. This is accomplished by extending the SU(3) Weinberg-Tomozawa chiral Lagrangian to SU(8) spin-flavor symmetry plus a suitable symmetry breaking. The model generates resonances with negative parity from the s-wave interaction of pseudoscalar and vector mesons with 1/2+ and 3/2+ baryons in all the isospin, spin, and strange sectors with one, two, and three charm units. Some of our results can be identified with experimental data from several facilities, such as the CLEO, Belle, or BaBar Collaborations, as well as with other theoretical models, whereas others do not have a straightforward identification and require the compilation of more data and also a refinement of the model.

hep-ph↗

arXiv2013

Review of low-energy interaction of strange and charm hadrons with nucleons and nuclei

The properties of strange and charm mesons in nuclear matter and nuclei are reviewed. Different frameworks are presented and discussed paying a special attention to unitarized coupled-channel approaches. Possible experimental signatures of the in-medium properties of these mesons are also addressed, in particular in connection with the future FAIR facility at GSI.

nucl-th↗

arXiv2012

Strangeness and Charm in Nuclear Matter

The properties of strange ($K$, $\bar K$ and $\bar K^*$) and open-charm ($D$, $\bar D$ and $D^*$) mesons in dense matter are studied using a unitary approach in coupled channels for meson-baryon scattering. In the strangeness sector, the interaction with nucleons always comes through vector-meson exchange, which is evaluated by chiral and hidden gauge Lagrangians. For the interaction of charmed mesons with nucleons we extend the SU(3) Weinberg-Tomozawa Lagrangian to incorporate spin-flavor symmetry and implement a suitable flavor symmetry breaking. The in-medium solution for the scattering amplitude accounts for Pauli blocking effects and meson self-energies. On one hand, we obtain the $K$, $\bar K$ and $\bar K^*$ spectral functions in the nuclear medium and study their behaviour at finite density, temperature and momentum. We also make an estimate of the transparency ratio of the $γA \to K^+ K^{*-} A^\prime$ reaction, which we propose as a tool to detect in-medium modifications of the $\bar K^*$ meson. On the other hand, in the charm sector, several resonances with negative parity are generated dynamically by the s-wave interaction between pseudoscalar and vector meson multiplets with $1/2^+$ and $3/2^+$ baryons. The properties of these states in matter are analyzed and their influence on the open-charm meson spectral functions is studied. We finally discuss the possible formation of $D$-mesic nuclei at FAIR energies.

nucl-th↗

arXiv2012

Recent Developments in Neutrino/Antineutrino - Nucleus Interactions

Recent experimental results and developments in the theoretical treatment of neutrino-nucleus interactions in the energy range of 1-10 GeV are discussed. Difficulties in extracting neutrino-nucleon cross sections from neutrino-nucleus scattering data are explained and significance of understanding nuclear effects for neutrino oscillation experiments is stressed. Detailed discussions of the status of two-body current contribution in the kinematic region dominated by quasi-elastic scattering and specific features of partonic nuclear effects in weak DIS scattering are presented.

hep-ex↗

arXiv2010

Heavy mesons in dense matter

Charmed mesons in dense matter are studied within a unitary coupled-channel approach which takes into account Pauli-blocking effects and meson self-energies in a self-consistent manner. We obtain the open-charm meson spectral functions in this dense medium, and discuss their implications on hidden charm and charm scalar resonances and on the formation of D-mesic nuclei.

nucl-th↗

arXiv2008

|Vub| from Exclusive Semileptonic B--> rho Decays

We use Omnes representations of the form factors V, A_1 and A_2 for exclusive semileptonic B--> rho decays, and apply them to combine experimental partial branching fraction information with theoretical calculations of the three form factors to extract |Vub|. We find a slightly lower result, |Vub|=(2.8 +- 0.2)x 10^{-3}, than the values extracted from exclusive semileptonic B-->pi decays and using all other inputs in CKM fits. The disagreement is greater when we compare to the result extracted from inclusive B -> X_u l nu decays.

hep-ph↗

arXiv2007

Photon induced Lambda(1520) production and the role of the K^* exchange

We study the photon induced Lambda(1520) production in the effective Lagrangian method near threshold, E_γ^{LAB}<2 GeV, and in the quark-gluon string model at higher energies 3 GeV < E_γ^{LAB} < 5 GeV. In particular, we study the role of the K^* exchange for the production of Lambda(1520) within the SU(6) Weinberg-Tomozowa chiral unitary model proposed in Phys. Rev. D74 (2006) 034025. The coupling of the Lambda(1520) resonance to the N \bar K^* pair, which is dynamically generated, turns out to be relatively small and, thus, the K exchange mechanism dominates the reaction. In the higher energy region, where experimental data are available, the quark-gluon string mechanism with the K Regge trajectory reproduces both the energy and the angular distribution dependences of the Lambda(1520) photo-production reaction.

hep-ph↗

arXiv2007

|Vub| from exclusive semileptonic B to pi decays revisited

We update the extraction of |Vub| from exclusive semileptonic B to pi decays, combining experimental partial branching fraction information with theoretical form factor calculations, using the recently revised HPQCD results for the form factors f_+ and f_0. We use Omnes representations to provide the required parametrisations of the form factors. The extracted value is 10^3 |Vub| = 3.47+/-0.29+/-0.03, in striking agreement with |Vub| extracted using all other inputs in CKM fits and showing some disagreement with |Vub| extracted from inclusive semileptonic B to pi decays.

hep-ph↗

arXiv2007

Semileptonic bc to cc Baryon Decay and Heavy Quark Spin Symmetry

We study the semileptonic decays of the lowest-lying bc baryons to the lowest-lying cc baryons (Xi_{bc}^{(\prime*)}--> Xi_{cc}^{(*)} and Omega_{bc}^{(\prime*)}--> Omega_{cc}^{(*)}), in the limit m_b, m_c >> Lambda_{QCD} and close to the zero recoil point. The separate heavy quark spin symmetries make it possible to describe all these decays using a single form factor. We recover results derived previously by White and Savage in a manner which we think is more straightforward and parallels the method applied later to study Bc semileptonic decays. We further discuss the resemblance between the bc baryon decays and those of Bc mesons to eta_c and J/ψmesons and comment on the relation between the slopes of the single functions describing each set of decays. Our results can straightforwardly be applied to the decays of bb baryons to bc baryons.

hep-ph↗

arXiv2007

|Vub| from Exclusive Semileptonic B to pi Decays

We use Omnes representations of the form factors f_+ and f_0 for exclusive semileptonic B to pi decays, paying special attention to the treatment of the B* pole and its effect on f_+. We apply them to combine experimental partial branching fraction information with theoretical calculations of both form factors to extract |Vub|. The precision we achieve is competitive with the inclusive determination and we do not find a significant discrepancy between our result, |Vub| =(3.90+/-0.32+/-0.18)10^(-3), and the inclusive world average value, (4.45+/-0.20+/-0.26)10^(-3).

hep-ph↗

arXiv2007

Elastic s-wave B pi, D pi, D K and K pi scattering from lattice calculations of scalar form factors in semileptonic decays

We show how theoretical, principally lattice, calculations of the scalar form factors in semileptonic pseudoscalar-to-pseudoscalar decays can be used to extract information about the corresponding elastic s-wave scattering channels. We find values for the scattering lengths m_pi a = 0.179(17)(14), 0.26(26) and 0.29(4) for elastic s-wave isospin-1/2 K pi, B pi and D pi channels respectively. We also determine phase shifts. For the D K channel we find hints that there is a bound state which can be identified with the recently discovered D_{s0}^+(2317).

hep-ph↗

arXiv2006

Extracting |V(ub)| from B->pi l nu Decays Using a Multiply-subtracted Omnes Dispersion Relation

We use a multiply-subtracted Omnes dispersion relation for the form factor f^+ in B->pi semileptonic decay, allowing the direct input of experimental and theoretical information to constrain its dependence on q^2. Apart from these inputs we use only unitarity and analyticity properties. We obtain |V(ub)|=(4.02 \pm 0.35)\times 10^{-3}, improving the agreement with the value determined from inclusive methods, and competitive in precision with them.

hep-ph↗

arXiv2001

The $S_{11}- N$(1535) and $-N$(1650) Resonances in Meson-Baryon Unitarized Coupled Channel Chiral Perturbation Theory

The $s-$wave meson-baryon scattering is analyzed for the strangeness S=0 sector in a Bethe-Salpeter coupled channel formalism incorporating Chiral Symmetry. Four channels have been considered: $πN$, $ηN$, $K Λ$, $K Σ$. The needed two particle irreducible matrix amplitude is taken from lowest order Chiral Perturbation Theory in a relativistic formalism and low energy constants are fitted to the elastic $πN $ phase-shifts and the $π^- p \to ηn$ and $π^- p \to K^0 Λ$ cross section data. The position of the complex poles in the second Riemann sheet of the scattering amplitude determine masses and widths of the $S_{11}-$ $N$(1535) and $-N$(1650) resonances, in reasonable agreement with experiment. A good overall description of data, from $πN$ threshold up to 2 GeV, is achieved keeping in mind that the two pion production channel has not been included.

hep-ph↗

arXiv1999

Bethe-Salpeter Approach for Meson-Meson Scattering in Chiral Perturbation Theory

The Bethe-Salpeter equation restores exact elastic unitarity in the s- channel by summing up an infinite set of chiral loops. We use this equation to show how a chiral expansion can be undertaken by successive approximations to the potential which should be iterated. Renormalizability of the amplitudes in a broad sense can be achieved by allowing for an infinite set of counter-terms as it is the case in ordinary Chiral Perturbation Theory. Within this framework we calculate the $ππ$ scattering amplitudes both for s- and p-waves at lowest order in the proposed expansion where a successful description of the low-lying resonances ($σ$ and $ρ$) and threshold parameters is obtained. We also extract the SU(2) low energy parameters ${\bar l}_{1,2,3,4}$ from our amplitudes.

nucl-th↗