arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 199 records · Page 11Linked to original sources

arXiv2012

On ambiguities of sign determination of the S-matrix from energy levels in a finite box

In a recent paper the authors make a study on the determination of the S-matrix elements for scattering of particles in the infinite volume from the energy levels in the finite box for the case of multiple channels. The study is done with a toy model in 1+1 dimension and the authors find that there is some ambiguity in the sign of nondiagonal matrix elements, casting doubts on whether the needed observables in the infinite volume can be obtained from the energy levels of the box. In this paper I present an easy derivation, confirming the ambiguity of the sign and argue that this, however, does not put restrictions in the determination of observables.

hep-lat↗

arXiv2012

Three methods to detect the predicted $D \bar{D}$ scalar meson X(3700)

In analogy to the f_0(500), which appears as a $ππ$ resonance in chiral unitary theory, and the f_0(980), which appears as a quasibound $K \bar K$ state, the extension of this approach to the charm sector also predicts a quasibound $D \bar D $ state with mass around 3720 MeV, named as X(3700), for which some experimental support is seen in the $e^+ e^- \to J/ψD \bar D $ reaction close to the $D \bar D $ threshold. In the present work we propose three different experiments to observe it as a clear peak. The first one is the radiative decay of the $ψ(3770)$, $ψ(3770) \to γX(3700) \to γηη'$. The second one proposes the analogous reaction $ψ(4040) \to γX(3700) \to γηη'$ and the third reaction is the $e^+ e^- \to J/ψX(3700) \to J/ψηη'$. Neat peaks are predicted for all the reactions and the calculated rates are found within measurable range in present facilities.

hep-ph↗

arXiv2012

Strategy to find the two $Λ(1405)$ states from lattice QCD simulations

Theoretical studies within the chiral unitary approach, and recent experiments, have provided evidence of the existence of two isoscalar states in the region of the $Λ(1405)$. In this paper we use the same chiral approach to generate energy levels in a finite box. In a second step, assuming that these energies correspond to lattice QCD results, we devise the best strategy of analysis to obtain the two states in the infinite volume case, with sufficient precision to distinguish them. We find out that using energy levels obtained with asymmetric boxes and/or with a moving frame, with reasonable errors in the energies, one has a successful scheme to get the two $Λ(1405)$ poles.

hep-lat↗

arXiv2012

Interaction of vector mesons with baryons and nuclei

After some short introductory remarks on particular issues on the vector mesons in nuclei, in this paper we present a short review of recent developments concerning the interaction of vector mesons with baryons and with nuclei from a modern perspective using the local hidden gauge formalism for the interaction of vector mesons. We present results for the vector baryon interaction and in particular for the resonances which appear as composite states, dynamically generated from the interaction of vector mesons with baryons, taking also the mixing of these states with pseudoscalars and baryons into account. We then venture into the charm sector, reporting on hidden charm baryon states around 4400 MeV, generated from the interaction of vector mesons and baryons with charm, which have a strong repercussion on the properties of the $J/ΨN$ interaction. We also address the interaction of $K^*$ with nuclei and make suggestions to measure the predicted huge width in the medium by means of the transparency ratio. The formalism is extended to study the phenomenon of $J/ψ$ suppression in nuclei via $J/ψ$ photoproduction reactions.

nucl-th↗

arXiv2012

Isospin breaking and $f_0(980)$-$a_0(980)$ mixing in the $η(1405) \to π^{0} f_0(980)$ reaction

We make a theoretical study of the $η(1405) \to π^{0} f_0(980)$ and $η(1405) \to π^{0} a_0(980)$ reactions with an aim to determine the isospin violation and the mixing of the $f_0(980)$ and $a_0(980)$ resonances. We make use of the chiral unitary approach where these two resonances appear as composite states of two mesons, dynamically generated by the meson-meson interaction provided by chiral Lagrangians. We obtain a very narrow shape for the $f_0(980)$ production in agreement with a BES experiment. As to the amount of isospin violation, or $f_0(980)$ and $a_0(980)$ mixing, assuming constant vertices for the primary $η(1405)\rightarrow π^{0}K\bar{K}$ and $η(1405)\rightarrow π^{0}π^{0}η$ production, we find results which are much smaller than found in the recent experimental BES paper, but consistent with results found in two other related BES experiments. We have tried to understand this anomaly by assuming an I=1 mixture in the $η(1405)$ wave function, but this leads to a much bigger width of the $f_0(980)$ mass distribution than observed experimentally. The problem is solved by using the primary production driven by $η' \to K^* \bar K$ followed by $K^* \to K π$, which induces an extra singularity in the loop functions needed to produce the $f_0(980)$ and $a_0(980)$ resonances. Improving upon earlier work along the same lines, and using the chiral unitary approach, we can now predict absolute values for the ratio $Γ(π^0, π^+ π^-)/Γ(π^0, π^0 η)$ which are in fair agreement with experiment. We also show that the same results hold if we had the $η(1475)$ resonance or a mixture of these two states, as seems to be the case in the BES experiment.

hep-ph↗

arXiv2012

The $DN$, $πΣ_c$ interaction in finite volume and the $Λ_c(2595)$ resonance

In this work the interaction of the coupled channels $DN$ and $πΣ_c$ in an SU(4) extrapolation of the chiral unitary theory, where the $Λ_c(2595)$ resonance appears as dynamically generated from that interaction, is extended to produce results in finite volume. Energy levels in the finite box are evaluated and, assuming that they would correspond to lattice results, the inverse problem of determining the phase shifts in the infinite volume from the lattice results is solved. We observe that it is possible to obtain accurate $πΣ_c$ phase shifts and the position of the $Λ_c(2595)$ resonance, but it requires the explicit consideration of the two coupled channels. We also observe that some of the energy levels in the box are attached to the closed $DN$ channel, such that their use to induce the $πΣ_c$ phase shifts via Lüscher's formula leads to incorrect results.

hep-ph↗

arXiv2012

Narrow bound states of the DNN system

We report on a recent calculation of the properties of the $DNN$ system, a charmed meson with two nucleons. The system is analogous to the $\bar K NN$ system substituting a strange quark by a charm quark. Two different methods are used to evaluate the binding and width, the Fixed Center approximation to the Faddeev equations and a variational calculation. In both methods we find that the system is bound by about 200 MeV and the width is smaller than 40 MeV, a situation opposite to the one of the $\bar K NN$ system and which makes this state well suited for experimental observation.

nucl-th↗

arXiv2012

Scalar mesons moving in a finite volume and the role of partial wave mixing

Phase shifts and resonance parameters can be obtained from finite-volume lattice spectra for interacting pairs of particles, moving with nonzero total momentum. We present a simple derivation of the method that is subsequently applied to obtain the pi pi and pi K phase shifts in the sectors with total isospin I=0 and I=1/2, respectively. Considering different total momenta, one obtains extra data points for a given volume that allow for a very efficient extraction of the resonance parameters in the infinite-volume limit. Corrections due to the mixing of partial waves are provided. We expect that our results will help to optimize the strategies in lattice simulations, which aim at an accurate determination of the scattering and resonance properties.

hep-lat↗

arXiv2012

The $X(3872) \to J/ψγ$ decay in the $D \bar D^*$ molecular picture

From a picture of the X(3872) where the resonance is a bound state of $\bar{D}D^*-c.c.$, we evaluate the decay width into the $J/ψγ$ channel, which is sensitive to the internal structure of this state. For this purpose we evaluate the loops through which the X(3872) decays into its components, and the $J/ψ$ and the photon are radiated from these components. We use the local hidden gauge approach extrapolated to SU(4) with a particular SU(4) breaking. The radiative decay involves anomalous couplings and we obtain acceptable values which are compared to experiments and results of other calculations. Simultaneusly, we evaluate the decay rate for the X(3872) into $J/ψω$ and $J/ψρ$, and the results obtained for the ratio of these decay widths are compatible with the experiment. We also show the grossly unacceptable results that come from taking only the $\bar{D}^0D^{*0}+c.c.$ component.

hep-ph↗

arXiv2012

A prediction of $D^*$-multi-$ρ$ states

We present a study of the many-body interaction between a $D^*$ and multi-$ρ$. We use an extrapolation to SU(4) of the hidden gauge formalism, which produced dynamically the resonances $f_2(1270)$ in the $ρρ$ interaction and $D^*_2(2460)$ in the $ρD^*$ interaction. Then let a third particle, $ρ$, $D^*$, or a resonance collide with them, evaluating the scattering amplitudes in terms of the Fixed Center Approximation of the Faddeev equations. We find several clear resonant structures above $2800\mev$ in the multibody scattering amplitudes. They would correspond to new charmed resonances, $D^*_3$, $D^*_4$, $D^*_5$ and $D^*_6$, which are not yet listed in the PDG, which would be analogous to the $ρ_3(1690)$, $f_4(2050)$, $ρ_5(2350)$, $f_6(2510)$ and $K^*_3(1780)$, $K^*_4(2045)$, $K^*_5(2380)$ described before as multi-$ρ$ and $K^*$-multi-$ρ$ states respectively.

hep-ph↗

arXiv2012

Wave functions of composite hadron states and relationship to couplings of scattering amplitudes for general partial waves

In this paper we present the connection between scattering amplitudes in momentum space and wave functions in coordinate space, generalizing previous work done for s-waves to any partial wave. The relationship to the wave function of the residues of the scattering amplitudes at the pole of bound states or resonances is investigated in detail. A sum rule obtained for the couplings provides a generalization to coupled channels, any partial wave and bound or resonance states, of Weinberg's compositeness condition, which was only valid for weakly bound states in one channel and s-wave. An example, requiring only experimental data, is shown for the $ρ$ meson indicating that it is not a composite particle of $ππ$ but something else.

hep-ph↗

arXiv2012

$J/ψ$ reaction mechanisms and suppression in the nuclear medium

Recent studies of the interaction of vector mesons with nuclei make possible and opportune the study of the interaction of the $J/ψ$ with nuclei and the investigation of the origin of the $J/ψ$ suppression in its propagation thorough a nuclear medium. We observe that the transition of $J/ψN$ to $VN$ with $V$ being a light vector, $ρ, ω,ϕ$, together with the inelastic channels, $J/ψN \to \bar D Λ_c$ and $J/ψN \to \bar D Σ_c$ leads to a particular shape of the inelastic cross section. Analogously, we consider the mechanisms where the exchanged $D$ collides with a nucleon and gives $πΛ_c$ or $πΣ_c$. The cross section has a peak around $\sqrt s=4415$ MeV, where the $J/ψN$ couples to a resonance predicted recently. We study the transparency ratio for electron induced $J/ψ$ production in nuclei at about 10 GeV and find that 30 - 35% of the $J/ψ$ produced in heavy nuclei are absorbed inside the nucleus. This ratio is in line with depletions of $J/ψ$ though matter observed in other reactions.

nucl-th↗

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

Improved Fixed Center Approximation of the Faddeev equations for the $\bar{K}NN$ system with S=0

We extend the Fixed Center Approximation (FCA) to the Faddeev Equations for the $\bar{K} NN$ system with S=0, including the charge exchange mechanisms in the $\bar{K}$ rescattering which have been ignored in former works within the FCA. We obtain similar results to those found before, but the binding is reduced by 6 MeV. At the same time we also evaluate the explicit contribution the $πN Σ$ intermediate state in the three body system and find that it produces and additional small decrease in the binding of about 3 MeV. The system appears bound by about 35 MeV and the width omitting two body absorption, is about 50 MeV.

nucl-th↗

arXiv2012

A narrow $DNN$ quasi-bound state

The energies and widths of $DNN$ quasi-bound states with isospin I=1/2 are evaluated in two methods, the fixed center approximation to the Faddeev equation and the variational method approach to the effective one-channel Hamiltonian. The $DN$ interactions are constructed so that they dynamically generate the $Λ_c(2595)$ (I=0, $J^π =1/2^-$) resonance state. We find that the system is bound by about 250 MeV from the $DNN$ threshold, $\sqrt{s} \sim 3500$ MeV. Its width including both the mesonic decay and the $D$ absorption, is estimated to be about 20-40 MeV. The I=0 $DN$ pair in the $DNN$ system is found to form a cluster that is similar to the $Λ_c(2595)$.

hep-ph↗

arXiv2012

Transparency ratio in γA -> η' A' and the in-medium η' width

The photoproduction of η'-mesons off different nuclei has been measured with the CBELSA/TAPS detector system for incident photon energies between 1500 - 2200 MeV. The transparency ratio has been deduced and compared to theoretical calculations describing the propagation of η'-mesons in nuclei. The comparison indicates a width of the η' -meson of the order of Γ= 15-25 MeV at ρ=ρ_0 for an average momentum p_{η'} = 1050 MeV/c, at which the η'-meson is produced in the nuclear rest frame. The inelastic η' N cross section is estimated to be 3 - 10 mb. Parameterizing the photoproduction cross section of η'-mesons by σ(A) = σ_0 A^α, a value of α= 0.84\pm0.03 has been deduced.

nucl-ex↗

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↗