arXiv subjects

L. Roca

Publications and source records attributed to L. Roca.

At least 37 records · Page 2Linked to original sources

arXiv2017

Role of a triangle singularity in the $πΔ$ decay of the $N(1700)(3/2^-)$

We show the important role played by the $πΔ(1232)$ channel in the build up of the $N(1700)(3/2^-)$ resonance due to the non-trivial enhancement produced by a singularity of a triangular loop. The $N(1700)$ is one of the dynamically generated resonances produced by the coupled channel vector-baryon interaction. The $πΔ$ channel was neglected in previous works but we show that it has to be incorporated into the coupled channel formalism due to an enhancement produced by a singularity in the triangular loop with $ρ$, nucleon and $π$ as internal loop lines and $π$ and $Δ$ as external ones. The enhancement is of non-resonant origin but it contributes to the dynamical generation of the $N(1700)$ resonance due to the non-linear dynamics involved in the coupled channel mechanisms. We obtain an important increase of the total width of the $N(1700)$ resonance when the $πΔ$ channel is included and provide predictions for the partial widths of the $N(1700)$ decays into $VB$ and $πΔ$.

hep-ph↗

arXiv2016

On the hidden charm pentaquark-s in $Λ_b \to J/ψK^- p$ decay

In a previous work we presented a theoretical analysis of the $Λ_b \to J/ψK^- p$ reaction from where a recent experiment by the LHCb collaboration at CERN claimed the existence of two hidden charm pentaquarks, $P_c(4380)^+$ and $P_c(4450)^+$. In that work we focused only on the $Λ(1405)$ and $P_c(4450)^+$ signals and discussed the possible explanation of this pentaquark state within the picture of a dynamical meson-baryon molecule made up mostly from $\bar D^* Σ_c$ and $\bar D^* Σ^*_c$ components. In the present work we improve upon the previous one by considering the total $K^- p$ and $J/ψp$ data including all the relevant resonances contributing to the spectra, and discuss the possible nature of both $P_c(4380)^+$ and $P_c(4450)^+$. We also discuss several important topics, like the effect of the contact term in the reaction, the viability of reproducing the data without the $P_c(4380)^+$ and the possible quantum numbers assignment to these pentaquarks.

hep-ph↗

arXiv2015

The LHCb pentaquark as a $\bar{D}^Σ_c-\bar{D}^Σ_c^*$ molecular state

We perform a theoretical analysis of the $Λ_b \to J/ψK^- p$ reaction from where a recent LHCb experiment extracts a $Λ(1405)$ contribution in the $K^- p$ spectrum close to threshold and two baryon states of hidden charm in the $J/ψ\,p$ spectrum. We recall that baryon states of this type have been theoretically predicted matching the mass, width and $J^P$ of the experiment, concretely some states built up from the $J/ψ\, N$, $\bar D^* Λ_c$, $\bar D^* Σ_c$, $\bar D Σ^*_c$ and $\bar D^* Σ^*_c$ coupled channels. We assume that the observed narrow state around 4450 MeV has this nature and we are able to describe simultaneously the shapes and relative strength of the the $K^- p$ mass distribution close to threshold and the peak of the $J/ψ\,p$ distribution, with values of the $J/ψ\, p$ coupling to the resonance in line with the theoretical ones. The non trivial matching of many properties gives support to a $J^P=3/2^-$ assignment to this state and to its nature as a molecular state mostly made of $\bar D^* Σ_c$ and $\bar D^* Σ^*_c$.

hep-ph↗

arXiv2015

Two, three, many body systems involving mesons. Multimeson condensates

In this talk we review results from studies with unconventional many hadron systems containing mesons: systems with two mesons and one baryon, three mesons, some novel systems with two baryons and one meson, and finally systems with many vector mesons, up to six, with their spins aligned forming states of increasing spin. We show that in many cases one has experimental counterparts for the states found, while in some other cases they remain as predictions, which we suggest to be searched in BESIII, Belle, LHCb, FAIR and other facilities.

hep-ph↗

arXiv2014

The composite nature of the $Λ(1520)$ resonance

Recently, the Weinberg compositeness condition of a bound state was generalized to account for resonant states and higher partial waves. We apply this extension to the case of the $Λ(1520)$ resonance and quantify the weight of the meson-baryon components in contrast to other possible genuine building blocks. This resonance was theoretically obtained from a coupled channels analysis using the s-waves $πΣ^*$, $KΞ^*$ and the d-waves $\bar{K}N$ and $πΣ$ channels applying the techniques of the chiral unitary approach. We obtain that this resonance is essentially dynamically generated from these meson-baryon channels, leaving room for only $15 \%$ weight of other kind of components into its wave function.

hep-ph↗

arXiv2013

On the isospin 0 and 1 resonances from $πΣ$ photoproduction data

Recently we presented a successful strategy to extract the position of the two $Λ(1405)$ poles from experimental photoproduction data on the $γp \to K^+ π^0 Σ^0 $ reaction at Jefferson Lab. Following a similar strategy, we extend the previous method to incorporate also the isospin 1 component which allows us to consider in addition the experimental data on $γp \to K^+ π^\pm Σ^\mp$. The idea is based on considering a production mechanism as model independent as possible and implementing the final state interaction of the final meson-baryon pair based on small modifications of the unitary chiral perturbation theory amplitudes. Good fits to the data are obtained with this procedure, by means of which we can also predict the cross sections for the $K^- p \to \bar K N$, $πΣ$, $πΛ$ reactions for the different charge channels. Besides the two poles found for the $Λ(1405)$ resonance, we discuss the possible existence of an isospin 1 resonance in the vicinity of the $\bar K N$ threshold.

nucl-th↗

arXiv2013

Finite volume treatment of $ππ$ scattering in the $ρ$ channel

We make a theoretical study of $ππ$ scattering with quantum numbers $J^{PC}=1^{--}$ in a finite box. To calculate physical observables for infinite volume from lattice QCD, the finite box dependence of the potentials is not usually considered. We quantify such effects by means of two different approaches for vector-isovector $ππ$ scattering based on Unitarized Chiral Perturbation Theory results: the Inverse Amplitude Method and another one based on the $N/D$ method. We take into account finite box effects stemming from higher orders through loops in the crossed $t,u-$channels as well as from the renormalization of the coupling constants. The main conclusion is that for $ππ$ phase shifts in the isovector channel one can safely apply Lüscher based methods for finite box sizes of $L$ greater than $2 m_π^{-1}$.

hep-lat↗

arXiv2013

Lambda(1405) poles obtained from pi0-Sigma0 photoproduction data

We present a strategy to extract the position of the two $Λ(1405)$ poles from experimental photoproduction data measured recently at different energies in the $γp \to K^+ π^0 Σ^0 $ reaction at Jefferson Lab. By means of a chiral dynamics motivated potential but with free parameters, we solve the Bethe Salpeter equation in the coupled channels $\bar K N$ and $πΣ$ in isospin I=0 and parameterize the amplitude for the photonuclear reaction in terms of a linear combination of the $πΣ\to πΣ$ and $\bar K N \to πΣ$ scattering amplitudes in I=0, with a different linear combination for each energy. Good fits to the data are obtained with some sets of parameters, by means of which one can also predict the cross section for the $K^- p \to π^0 Σ^0 $ reaction. These later results help us decide among the possible solutions. The result is that the different solutions lead to two poles similar to those found in the chiral unitary approach. With the best result we find the two $Λ(1405)$ poles at $1385-68i\mev$and $1419-22i\mev$.

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arXiv2012

Isospin violation in J/Psi to phi pi0 eta decay and the f0-a0 mixing

The isospin violating $J/Ψ\to ϕπ^0 η$ decay is thought to be dominated by the mixing of the $f_0(980)$ and $a_0(980)$ scalar resonances. We make a theoretical evaluation of the $J/Ψ\to ϕπ^0 η$ decay extending our own previous model for other $J/Ψ$ decays into one vector meson and two pseudoscalars using the techniques of the chiral unitary approach. The scalar resonances are dynamically generated through the final state interaction of the pseudoscalar mesons implementing unitarity from the lowest order ChPT amplitudes. Besides the direct $J/ΨϕPP$ vertex, other mechanisms like the sequential exchange of vector and axial-vector mesons are shown to be important in order to obtain the actual strength of the mixing. We get a very good agreement with the $π^0 η$ invariant mass distribution and branching ratio with recent BESIII data. Quantification of the $f_0(980)-a_0(980)$ mixing is done and compared with results from several experiments.

hep-ph↗

arXiv2012

Finite volume treatment of pi pi scattering and limits to phase shifts extraction from lattice QCD

We study theoretically the effects of finite volume for pipi scattering in order to extract physical observables for infinite volume from lattice QCD. We compare three different approaches for pipi scattering (lowest order Bethe-Salpeter approach, N/D and inverse amplitude methods) with the aim to study the effects of the finite size of the box in the potential of the different theories, specially the left-hand cut contribution through loops in the crossed t,u-channels. We quantify the error made by neglecting these effects in usual extractions of physical observables from lattice QCD spectra. We conclude that for pipi phase-shifts in the scalar-isoscalar channel up to 800 MeV this effect is negligible for box sizes bigger than 2.5m_pi^-1 and of the order of 5% at around 1.5-2m_pi^-1. For isospin 2 the finite size effects can reach up to 10% for that energy. We also quantify the error made when using the standard Luscher method to extract physical observables from lattice QCD, which is widely used in the literature but is an approximation of the one used in the present work.

hep-lat↗

arXiv2012

Momentum dependence of the phi-meson nuclear transparency

The production of phi mesons in proton collisions with C, Cu, Ag, and Au targets has been studied via the phi -> K+K- decay at an incident beam energy of 2.83 GeV using the ANKE detector system at COSY. For the first time, the momentum dependence of the nuclear transparency ratio, the in-medium phi width, and the differential cross section for phi meson production at forward angles have been determined for these targets over the momentum range of 0.6 - 1.6 GeV/c. There are indications of a significant momentum dependence in the value of the extracted phi width, which corresponds to an effective phi-N absorption cross section in the range of 14 - 21 mb.

nucl-ex↗

arXiv2012

Scattering of unstable particles in a finite volume: the case of pi rho scattering and the a1(1260) resonance

We present a way to evaluate the scattering of unstable particles quantized in a finite volume with the aim of extracting physical observables for infinite volume from lattice data. We illustrate the method with the $πρ$ scattering which generates dynamically the axial-vector $a_1(1260)$ resonance. Energy levels in a finite box are evaluated both considering the $ρ$ as a stable and unstable resonance and we find significant differences between both cases. We discuss how to solve the problem to get the physical scattering amplitudes in the infinite volume, and hence phase shifts, from possible lattice results on energy levels quantized inside a finite box.

hep-lat↗

arXiv2011

Two, three, many body systems involving mesons

In this talk we show recent developments on few body systems involving mesons. We report on an approach to Faddeev equations using chiral unitary dynamics, where an explicit cancellation of the two body off shell amplitude with three body forces stemming from the same chiral Lagrangians takes place. This removal of the unphysical off shell part of the amplitudes is most welcome and renders the approach unambiguous, showing that only on shell two body amplitudes need to be used. Within this approach, systems of two mesons and one baryon are studied, reproducing properties of the low lying $1/2^+$ states. On the other hand we also report on multirho and $K^*$ multirho states which can be associated to known meson resonances of high spin.

nucl-th↗

arXiv2011

Pseudotensor mesons as three-body resonances

We show that the lightest pseudotensor mesons J^{PC}=2^-+ can be regarded as molecules made of a pseudoscalar (P) 0^-+ and a tensor 2^++ meson, where the latter is itself made of two vector (V) mesons. The idea stems from the fact that the vector-vector interaction in s-wave and spin 2 is very strong, to the point of generating the 2^++ tensor mesons. On the other hand the interaction of a pseudoscalar with a vector meson in s-wave is also very strong and it generates dynamically the lightest axial-vector mesons. Therefore we expect the PVV interaction to be strongly attractive and thus able to build up quasibound PVV resonances. We calculate the three body PVV interaction by using the fixed center approximation to the Faddeev equations where the two vectors are clustered forming a tensor meson. We find clear resonant structures which can be identified with the pi_2(1670), eta_2(1645) and K^*_2(1770) (2^-+) pseudotensor mesons.

hep-ph↗

arXiv2011

Selected topics on Hadrons in Nuclei

In this talk we report on selected topics on hadrons in nuclei. The first topic is the renormalization of the width of the $Λ(1520)$ in a nuclear medium. This is followed by a short update of the situation of the $ω$ in the medium. The investigation of the properties of $\bar{K}$ in the nuclear medium from the study of the $(K_{flight},p)$ reaction is also addressed, as well as properties of X,Y,Z charmed and hidden charm resonances in a nuclear medium. Finally we address the novel issue of multimeson states.

nucl-th↗

arXiv2010

Hadron resonances generated from the dynamics of the lightest scalar ones

We have studied the interactions of the scalar resonances f_0(980) and a_0(980) with the vector resonance ϕ(1020) and with the lightest pseudoscalars π, K, ηand η'. We first obtain the interaction kernels without including any new free parameter. Afterwards, the interaction kernels are unitarized and the final S-wave amplitudes result. We find that these interactions are very rich and generate a large amount of pseudoscalar resonances including the K(1460), π(1300), π(1800), η(1475) and X(1835) resonances. The f_0(980)ϕ(1020) self-interactions give rise to the ϕ(2170) resonance. For realistic choices of the parameters we also obtain an isovector companion in the same mass region from the a_0(980) ϕ(1020) interactions.

hep-ph↗

arXiv2010

Dynamical generation of pseudoscalar resonances

We study the interactions between the f_0(980) and a_0(980) scalar resonances and the lightest pseudoscalar mesons. We first obtain the elementary interaction amplitudes, or interacting kernels, without including any ad hoc free parameter. This is achieved by using previous results on the nature of the lightest scalar resonances as dynamically generated from the rescattering of S-wave two-meson pairs. Afterwards, the interaction kernels are unitarized and the final S-wave amplitudes result. We find that these interactions are very rich and generate a large amount of pseudoscalar resonances that could be associated with the K(1460), π(1300), π(1800), η(1475) and X(1835). We also consider the exotic channels with isospin 3/2 and 1, having the latter positive G-parity. The former could be also resonant in agreement with a previous prediction.

hep-ph↗

arXiv2010

Three body systems with strangeness and exotic systems

We report on four $Σ$'s and three $Λ$'s, in the 1500 - 1800 MeV region, as two meson - one baryon S-wave $(1/2)^+$ resonances found by solving the Faddeev equations in the coupled channel approach, which can be associated to the existing $S$ = -1, $J^P= 1/2^+$ low lying baryon resonances. On the other hand we also report on a new, hidden strangeness $N^*$ state, mostly made of $K \bar{K} N$, with mass around 1920 MeV, which we think could be responsible for the peak seen in the $γp \to K^+ Λ$ around this energy. Finally we address a very novel topic in which we show how few body systems of several $ρ$ mesons can be produced, with their spins aligned up to J=6, and how these states found theoretically can be associated to several known mesons with spins J=2,3,4,5,6.

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