arXiv subjects

A. Martinez Torres

Publications and source records attributed to A. Martinez Torres.

At least 55 records · Page 3Linked to original sources

arXiv2015

A study of the $KN$-$K^*N$ coupled systems

We study the strangeness $+1$ meson-baryon systems to obtain improved $KN$ and $K^*N$ amplitudes and to look for a possible resonance formation by the $KN$-$K^*N$ coupled interaction. We obtain amplitudes for light vector meson-baryon systems by implementing the $s$-, $t$-, $u$- channel diagrams and a contact interaction. The pseudoscalar meson-baryon interactions are obtained by relying on the Weinberg-Tomozawa theorem. The transition amplitudes between the systems consisting of pseudoscalars and vector mesons are calculated by extending the Kroll-Ruderman term for pion photoproduction replacing the photon by a vector meson. We fix the subtraction constants required to calculate the loops by fitting our $KN$ amplitudes to the data available for the isospin 0 and 1 $s$-wave phase shifts. We provide the scattering lengths and the total cross sections for the $KN$ and $K^* N$ systems obtained in our model, which can be useful in future in-medium calculations. Our amplitudes do not correspond to formation of any resonance in none of the isospin and spin configurations.

nucl-th↗

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

$X(3872)$ production from reactions involving $D$ and $D^*$ mesons

In this proceeding we show the results found for the cross sections of the processes $\bar D D\toπX(3872)$, $\bar D^* D\to πX(3872)$ and $\bar D^* D^*\toπX(3872)$, information needed for calculations of the $X(3872)$ abundance in heavy ion collisions. Our formalism is based on the generation of $X(3872)$ from the interaction of the hadrons $\bar D^0 D^{*0} - \textrm{c.c}$, $D^- D^{*+} - \textrm{c.c}$ and $D^-_s D^{*+}_s - \textrm{c.c}$. The evaluation of the cross section associated with processes having $D^*$ meson(s) involves an anomalous vertex, $X\bar D^* D^*$, which we have determined by considering triangular loops motivated by the molecular nature of $X(3872)$. We find that the contribution of this vertex is important. Encouraged by this finding we estimate the $X\bar D^* D^*$ coupling, which turns out to be $1.95\pm 0.22$. We then use it to obtain the cross section for the reaction $\bar D^* D^*\toπX$ and find that the $X\bar D^* D^*$ vertex is also relevant in this case. We also discuss the role of the charged components of $X$ in the determination of the production cross sections.

hep-ph↗

arXiv2014

$X(3872)$ production in high energy heavy ion collisions

We show the results obtained for the cross sections of the processes $\bar D D$, $\bar D^* D$, $\bar D^* D^*\toπX(3872)$, information which is necessary to determine the $X(3872)$ abundance in heavy ion collisions. Our formalism is based on the generation of $X(3872)$ from the interaction of the hadrons $\bar D^0 D^{*0} - \textrm{c.c}$, $D^- D^{*+} - \textrm{c.c}$ and $D^-_s D^{*+}_s - \textrm{c.c}$ an the calculation of the $X\bar D^* D^*$ anomalous vertex considering $X(3872)$ as a molecule of the above hadrons channels.

hep-ph↗

arXiv2014

Signature of an $h_1$ state from $J/ψ\to ηK^{0}\bar{K}^{0}$ and theoretical description of the $Z_c(3900)$ and $Z_c(4020)$ as $D \bar D^$ and $D^ \bar D^*$ molecular states

In this talk we address two topics: The first one is an empirical explanation in terms of a new state $h_1$ of the peak in the $K^{*0}\bar{K}^{*0}$ invariant mass distribution close to threshold of this channel in the $J/ψ\to ηK^{*0}\bar{K}^{*0}$ decay. The second one is a theoretical description of the isospin $I=1$ $Z_c(3900)$ and $Z_c(4020)$ states in terms of molecular states of $D \bar D^*+ cc$ and $D^* \bar D^*$.

hep-ph↗

arXiv2014

Prediction of an $I=1$ $D \bar D^*$ state and relationship to the claimed $Z_c(3900)$, $Z_c(3885)$

We study here the interaction of $D \bar D^*$ in the isospin $I=1$ channel in the light of recent theoretical advances that allow to combine elements of the local hidden gauge approach with heavy quark spin symmetry. We find that the exchange of light $q \bar q$ is OZI suppressed and, thus, we concentrate on the exchange of heavy vectors and of two pion exchange. The latter is found to be small compared to the exchange of heavy vectors, which then determines the strength of the interaction. A barely $D\bar{D}^*$ bound state decaying into $η_cρ$ and $πJ/ψ$ is found. At the same time we reanalyze the data of the BESIII experiment on $e^+ e^- \to π^{\pm} (D \bar D^*)^\mp$, from where a $Z_c(3885)$ state was claimed, associated to a peak in the $(D \bar D^*)^\mp$ invariant mass distribution close to threshold, and we find the data compatible with a resonance with mass around $3875$ MeV and width around $30$ MeV. We discuss the possibility that this and the $Z_c(3900)$ state found at BESIII, reconfirmed at 3896 MeV at Belle, or 3885 MeV at CLEO, could all be the same state and correspond to the one that we find theoretically.

hep-ph↗

arXiv2014

On $X(3872)$ production in high energy heavy ion collisions

We have determined the production cross sections of the $X(3872)$ state in the reactions $\bar D D\toπX$, $\bar D^* D\to πX$ and $\bar D^* D^*\toπX$, information which is useful for studies of the $X(3872)$ meson abundance in heavy ion collisions. We construct a formalism considering $X$ as a molecular bound state of $\bar D^0 D^{*0} - \textrm{c.c}$, $D^- D^{*+} - \textrm{c.c}$ and $D^-_s D^{*+}_s - \textrm{c.c}$. To obtain the amplitudes related to these processes we have made use of effective field Lagrangians. The evaluation of the cross section of the processes involving $D^*$ meson(s) requires the calculation of an anomalous vertex, $X\bar D^* D^*$, which has been obtained by considering triangular loops motivated by the molecular nature of $X(3872)$. Proceeding in this way, we have evaluated the cross section for the reaction $\bar D^* D\to πX$, and find that the diagrams involving the $X\bar D^* D^*$ vertex give a large contribution. Encouraged by this finding we estimate the $X\bar D^* D^*$ coupling, which turns out to be $1.95\pm 0.22$. We then use it to obtain the cross section for the reaction $\bar D^* D^*\toπX$ and find that, in this case too, the $X\bar D^* D^*$ vertex is relevant. We also discuss the role of the charged components of $X$ in the determination of the production cross sections.

hep-ph↗

arXiv2013

Study of the $D^*ρ$ system using QCD sum rules

In this talk I present a study of the $D^* ρ$ system made by using the method of QCD sum rules. Considering isospin and spin projectors, we investigate the different configurations and obtain three $D^*$ mesons with isospin $I=1/2$, spin $S=0$, $1$, $2$ and with masses $2500\pm 67$ MeV, $2523\pm60$ MeV, and $2439\pm119$ MeV, respectively. The last state can be related to $D^*_2(2460)$ (spin 2) listed by the Particle Data Group, while one of the first two might be associated with $D^*(2640)$, whose spin-parity is unknown. In the case of $I=3/2$ we also find evidences of three states with spin 0, 1 and 2, respectively, with masses $2467\pm82$ MeV, $2420\pm128$ MeV, and $2550\pm56$ MeV.

hep-ph↗

arXiv2013

Interpreting the peak structures around 1800 MeV in the BES data on $J/Ψ\to ϕπ^+ π^-$, $J/Ψ\to γωϕ$

In this talk we present an interpretation for the experimental data available on two different processes, namely, $J/Ψ\to ϕπ^+ π^-$, $J/Ψ\to γωϕ$, which seem to indicate existence of two new resonances with the same quantum numbers ($J^{πc}=0^{++}, I = 0$) and very similar mass (~1800 MeV) but with very different decay properties. However, our studies show that the peak structure found in the $ωϕ$ invariant mass, in $J/Ψ\to γωϕ$, is a manifestation of the well known $f_0(1710)$ while the cross section enhancement found in $J/Ψ\to ϕπ^+ π^-$ is indeed a new $f_0$ resonance with mass near 1800 MeV. We present an explanation for the different decay properties of these two scalar resonances.

hep-ph↗

arXiv2013

Relating $D^* \bar{D}^*$ currents with $J^π= 0^+,1^+$ and $2^+$ to $Z_c$ states

In this work we study the $D^* \bar{D}^*$ current with QCD sum rules. We write the correlation function using the general current corresponding to the $D^* \bar{D}^*$ system and then use spin projectors to obtain the correlation function in the $0^+, 1^+$ and $2^+$ spin-parity configurations. The purpose of the present work is to investigate the possibility of explaining the recently reported $Z_c(4025)$ as a $D^* \bar{D}^*$ moleculelike state. As a result we find a state for each spin case with a very similar mass: $M^{S=0} = \left(3943 \pm 104\right)$ MeV, $M^{S=1} = \left(3950 \pm 105\right)$ MeV, $M^{S=2} = \left(3946 \pm 104 \right)$ MeV. We discuss that our mass results, within error bars, for $1^+$ or $2^+$ are both compatible with $Z_c(4025)$. However, our results are also compatible with a possible $D^* \bar{D}^*$ bound state, in agreement with predictions of some previous works. We have also calculated the current-state coupling which turns out to be larger in the $2^+$ case.

hep-ph↗

arXiv2012

A new perspective on the Faddeev equations and the $\bar{K}NN$ system from chiral dynamics and unitarity in coupled channels

We review recent work concerning the $\bar{K}N$ interaction and Faddeev equations with chiral dynamics which allow us to look at the $\bar{K}NN$ from a different perspective and pay attention to problems that have been posed in previous studies on the subject. We show results which provide extra experimental evidence on the existence of two $Λ(1405)$ states. We then show the findings of a recent 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. With this information in mind we use an approximation to the Faddeev equations within the fixed center approximation to study the $\bar{K}NN$ system, providing answers within this approximation to questions that have been brought before and evaluating binding energies and widths of this three body system. As a novelty with respect to recent work on the topic we find a bound state of the system with spin S=1, like a bound state of $\bar{K}$-deuteron, less bound that the one of S=0, where all recent efforts have been devoted. The width is relatively large in this case, suggesting problems in a possible experimental observation.

hep-ph↗

arXiv2012

Interaction of vector mesons with baryons and vectors in the nuclear medium

In this talk we present a short review of recent developments concerning the interaction of vector mesons with baryons and with nuclei. We begin with the hidden gauge formalism for the interaction of vector mesons, then review results for vector baryon interaction and in particular the resonances which appear as composite states, dynamically generated from the interaction of vector mesons with baryons. New developments concerning the mixing of these states with pseudoscalars and baryons are also reported. We include some discussion on the $5/2^+$ $Δ$ resonances around 2000 MeV, where we suggest that the $Δ(2000)5/2^+$ resonance, which comes in the PDG from averaging a set of resonances appearing around 1700 MeV and another one around 2200 MeV, corresponds indeed to two distinct resonances. We also report on a hidden charm baryon state around 4400 MeV coming from the interaction of vector mesons and baryons with charm, and how this state has some repercussion in the $J/ψ$ suppression in nuclei. The interaction of $K^*$ in nuclei is also reported and suggestions are made to measure by means of the transparency ratio the huge width in the medium that the theoretical calculations predict. The formalism is extended to $J/ψ$ interaction with nuclei and the transparency ratio for $J/ψ$ photoproduction in nuclei is studied and shown to be a good tool to find possible baryon states which couple to $J/ψN$.

nucl-th↗

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

Delta rho pi interaction leading to N* and Delta* resonances

We have performed a calculation for the three body $Δρπ$ system by using the fixed center approximation to Faddeev equations, taking the interaction between $Δ$ and $ρ$, $Δ$ and$π$, and $ρ$ and $π$ from the chiral unitary approach. We find several peaks in the modulus squared of the three-body scattering amplitude, indicating the existence of resonances, which can be associated to known $I=1/2, 3/2$ and $J^P=1/2^+, 3/2^+$ and $5/2^+$ baryon states.

nucl-th↗

arXiv2010

Critical view of the claimed $Θ^+$ pentaquark

We use a theoretical model of the $γ~d \to ~K^+ K^- ~n ~p $ reaction adapted to the experiment done at LEPS where a peak was observed and associated to the $Θ^{+}(1540)$ pentaquark. The study shows that the method used in the experiment to associate momenta to the undetected proton and neutron, together with the chosen cuts, necessarily creates an artificial broad peak in the assumed $K^+ n$ invariant mass in the region of the claimed $Θ^{+}(1540)$. It is shown that the LEPS fit to the data, used to make the claim of the $Θ^{+}(1540)$, grossly distorts the background. An alternative fit, assuming a background plus a fluctuation, returns a background practically equal to the theoretical one and a fluctuation identical to the one seen in the experimental $K^- p$ spectrum of 2$σ$ significance.

nucl-th↗

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.

nucl-th↗

arXiv2010

Review on dynamically generated resonances

We present recent results on the vector meson-vector meson and vector meson-baryon interaction using a unitary approach based on the hidden-gauge Lagrangians. For the vector-vector case we find that 11 states get dynamically generated, corresponding to poles of the scattering matrices on the second Riemann sheet. In the vector-baryon sector we also find 9 states dynamically generated from the vector-baryon octet interaction and 10 from the vector-baryon decuplet interaction. We also report on baryon states found from the interaction of two mesons and a baryon.

hep-ph↗

arXiv2010

Study of the $J/ψ\to ϕ(ω) f_2(1270)$, $J/ψ\to ϕ(ω) f'_2(1525)$ and $J/ψ\to K^{0}(892) \bar{K}^{ 0}_2(1430)$ decays

We present an approach to study the decay modes of the $J/ψ$ into a vector meson and a tensor meson, taking into account the nature of the $f_2(1270)$, $f'_2(1525)$, $\bar{K}^{* 0}_2(1430)$ resonances as dynamically generated states from the vector meson-vector meson interaction. We evaluate four ratios of partial decay widths in terms of a flavor dependent OZI breaking parameter and the results obtained compare favorably with experiment. The fit to the data is possible due to the particular strength and sign of the couplings of the resonances to pairs of vector mesons given by the theory, thus providing a nontrivial test for the idea of these tensor states as dynamically generated from the vector-vector interaction.

nucl-th↗