arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 73 records · Page 4Linked to original sources

arXiv2020

Molecular picture for the $X_0(2866)$ as a $D^* \bar{K}^*$ $J^P=0^+$ state and related $1^+,2^+$ states

We recall the predictions made ten years ago about a bound state of $J^P=0^+$ in $I=0 $ of the $D^* \bar{K}^*$ system, which is manifestly exotic, and we associate it to the $X_0(2866)$ state reported in the recent LHCb experiment. Fine tuning the parameters to reproduce exactly the mass and width of the $X_0(2866)$ state, we report two more states stemming from the same interaction, one with $1^+$ and the other with $2^+$. For reasons of parity, the $1^+$ state cannot be observed in $D\bar{K}$ decay, and we suggest to observe it in the $D^*\bar{K}$ spectrum. On the other hand, the $2^+$ state can be observed in $D \bar{K}$ decay but the present experiment has too small statistics in the region of its mass to make any claim. We note that measurements of the $D^*\bar{K}$ spectrum and of the $D \bar{K}$ with more statistics should bring important information concerning the nature of the $X_0(2866)$ and related ones that could be observed.

hep-ph↗

arXiv2020

Few-body systems consisting of mesons

We present a work which is meant to inspire the few-body practitioners to venture into the study of new, more exotic, systems and to hadron physicists, working mostly on two-body problems, to move in the direction of studying related few-body systems. For this purpose we devote the discussions in the introduction to show how the input two-body amplitudes can be easily obtained using techniques of the chiral unitary theory, or its extensions to the heavy quark sector. We then briefly explain how these amplitudes can be used to solve the Faddeev equations or a simpler version obtained by treating the three-body scattering as that of a particle on a fixed center. Further, we give some examples of the results obtained by studying systems involving mesons. We have also addressed the field of many meson systems, which is currently almost unexplored, but for which we envisage a bright future. Finally, we give a complete list of works dealing with unconventional few-body systems involving one or several mesons, summarizing in this way the findings on the topic, and providing a motivation for those willing to investigate such systems.

nucl-th↗

arXiv2020

Tau decay into $ν_τ$ and $a_1(1260)$, $b_1(1235)$, and two $K_1(1270)$

We study the $τ\to ν_τA$ decay, with $A$ an axial-vector meson. We produce the $a_1(1260)$ and $b_1(1235)$ resonances in the Cabibbo favored mode and two $K_1(1270)$ states in the Cabibbo suppressed mode. We take advantage of previous chiral unitary approach results where these resonances appear dynamically from the vector and pseudoscalar meson interaction in s-wave. Actually two different poles were obtained associated to the $K_1(1270)$ quantum numbers. We find that the unmeasured rates for $b_1(1235)$ production are similar to those of the $a_1(1260)$ and for the two $K_1$ states we suggest to separate the present information on the $\bar K ππ$ invariant masses into $\bar K^* π$ and $ρK$ modes, the channels to which these two resonances couple most strongly, predicting that these modes peak at different energies and have different widths. These measurements should shed light on the existence of these two $K_1$ states.

hep-ph↗

arXiv2020

$Ξ_{bb}$ and $Ω_{bbb}$ molecular states

Using the vector-exchange interaction in the local hidden gauge approach, which in the light quark sector generates the chiral Lagrangian, and has produced realistic results for $Ω_c, Ξ_c, Ξ_b$ and the hidden charm pentaquark states, we study the meson-baryon interactions in the coupled channels that lead to the $Ξ_{bb}$ and $Ω_{bbb}$ excited states of the molecular type. We obtain seven states of the $Ξ_{bb}$ type with energies between $10408$ and $10869$ MeV and one $Ω_{bbb}$ state at $15212$ MeV.

hep-ph↗

arXiv2020

Observed $Ω_b$ spectrum and meson-baryon molecular states

We observe that four peaks seen in the high energy part of the $Ω_b$ spectrum of the recent LHCb experiment are in remarkable agreement with predictions made for molecular $Ω_b$ states stemming from the meson-baryon interaction, with an approach that applied to the $Ω_c$ states gave rise to three states in good agreement with experiment in masses and widths. While the statistical significance of the peaks prevents us from claims of states at the present time, the agreement found should be an incentive to look at this experiment with increased statistics to give an answer to this suggestive idea.

hep-ph↗

arXiv2020

Analysis of the $ψ(4040)$ and $ψ(4160)$ decay into $D^{(\ast)} \bar D^{(\ast)}$, $D_s^{(\ast)}\bar D_s^{(\ast)}$

We have performed an analysis of the $e^+ e^- \to D^{(*)} \bar D^{(*)}$ data in the region of the $ψ(4040)$ and $ψ(4160)$ resonances which have a substantial overlap and require special care. By using the $^3 P_0$ model to relate the different $D^{(*)} \bar D^{(*)}$ production modes, we make predictions for production of these channels and compare with experiment and other theoretical approaches. As a side effect we find that these resonances qualify largely as $c \bar c$ states and the weight of the meson-meson components in the wave function is very small.

hep-ph↗

arXiv2020

$J/ψ\to γππ$, $γπ^0η$ reactions and the $f_0(980)$ and $a_0(980)$ resonances

We study the $J/ψ\to γπ^+ π^-$, $γπ^0 η$ reactions from the perspective that they come from the $J/ψ\to ϕ(ω) π^+ π^-, ρ^0π^0 η$ reactions, where the $ρ^0$, $ω$, and $ϕ$ get converted into a photon via vector meson dominance. Using models successfully used previously to study the $J/ψ\to ω(ϕ) ππ$ reactions, we make determinations of the invariant mass distributions for $π^+ π^-$ in the regions of the $f_0(500)$, $f_0(980)$, and for $π^0 η$ in the region of the $a_0(980)$. The integrated differential widths lead to branching ratios below present upper bounds, but they are sufficiently large for future check in updated facilities.

hep-ph↗

arXiv2020

Testing the origin of the "$f_1(1420)$" with the $\bar K p \to Λ(Σ) K\bar K π$ reaction

We study the $\bar K p \to Y K\bar K π$ reactions with $\bar K = \bar K^0, K^-$ and $Y=Σ^0, Σ^+, Λ$, in the region of $K\bar K π$ invariant masses of $1200-1550$ MeV. The strong coupling of the $f_1(1285)$ resonance to $K^* \bar K$ makes the mechanism based on $K^*$ exchange very efficient to produce this resonance observed in the $K\bar K π$ invariant mass distribution. In addition, in all the reactions one observes an associated peak at $1420$ MeV which comes from the $K^* \bar K$ decay mode of the $f_1(1285)$ when the $K^*$ is placed off shell at higher invariant masses. We claim this to be the reason for the peak of the $K^* \bar K$ distribution seen in the experiments which has been associated to the "$f_1(1420)$" resonance.

hep-ph↗

arXiv2019

Molecular $Ξ_{bc}$ states from meson-baryon interaction

We have studied the meson-baryon interaction in coupled channels with the same quantum numbers of $Ξ_{bc}$. The interaction is attractive in some channels and of sufficient intensity to lead to bound states or resonances. We use a model describing the meson-baryon interaction based on an extrapolation of the local hidden gauge approach to the heavy sector, which has been successfully used in predicting $Ω_c$ and hidden charm states. We obtain many states, some of them narrow or with zero width, as a consequence of the interaction, which qualify as molecular states in those channels. The success in related sectors of the picture used should encourage the experimental search for such states.

hep-ph↗

arXiv2019

$J/ψ$ decay into $ϕ(ω)$ and vector-vector molecular states

Based on the picture that the $ f_0(1370), f_0(1710), f_2(1270), f'_2(1525), \bar{K}^{*0}_2(1430)$ resonances are dynamically generated from the vector-vector interaction, we study the decays $J/ψ\to ϕ(ω) f_0(1370) [f_0(1710)]$, $J/ψ\to ϕ(ω) f_2(1270) [f'_2(1525)]$, and $J/ψ\to K^{*0} \bar{K}^{*0}_2(1430)$ and make predictions for seven independent ratios that can be done among them. The starting mechanism is that the $J/ψ$ decays into three vectors, followed by the final state interaction of a pair of them. The weights of the different three vector primary channels are obtained from the basic assumption that the $J/ψ$ ($c \bar c$) is an SU(3) singlet. By means of only one free parameter we predict four ratios in good agreement with experiment, make two extra predictions for rates yet unmeasured, and disagree on one data for which only upper bounds are reported. Further measurements are most welcome to complete the information required for these ratios that are testing the nature of these resonances as dynamically generated.

hep-ph↗

arXiv2019

Comments on the dispersion relation method to vector-vector interaction

We study in detail the method proposed recently to study the vector-vector interaction using the $N/D$ method and dispersion relations, which concludes that, while for $J=0$, one finds bound states, in the case of $J=2$, where the interaction is also attractive and much stronger, no bound state is found. In that work, approximations are done for $N$ and $D$ and a subtracted dispersion relation for $D$ is used, with subtractions made up to a polynomial of second degree in $s-s_\mathrm{th}$, matching the expression to $1-VG$ at threshold. We study this in detail for the $ρ- ρ$ interaction and to see the convergence of the method we make an extra subtraction matching $1-VG$ at threshold up to $(s-s_\mathrm{th})^3$. We show that the method cannot be used to extrapolate the results down to 1270 MeV where the $f_2(1270)$ resonance appears, due to the artificial singularity stemming from the "on shell" factorization of the $ρ$ exchange potential. In addition, we explore the same method but folding this interaction with the mass distribution of the $ρ$, and we show that the singularity disappears and the method allows one to extrapolate to low energies, where both the $(s-s_\mathrm{th})^2$ and $(s-s_\mathrm{th})^3$ expansions lead to a zero of $\mathrm{Re}\,D(s)$, at about the same energy where a realistic approach produces a bound state. Even then, the method generates a large $\mathrm{Im}\,D(s)$ that we discuss is unphysical.

hep-ph↗

arXiv2019

Helicity amplitudes in the $\bar{B} \to D^{*} \barν_ττ$ decay with $V-A$ breaking in the quark sector

In view of the recent measurement of the $F_L^{D^*}$ magnitude in the $\bar{B} \to D^{*} \barν_ττ$ reaction we evaluate this magnitude within the standard model and for a family of models with the $γ^μ-αγ^μγ_5$ current structure for the quarks for different values of $α$. At the same time we evaluate also the transverse contributions, $M=-1$, $M=+1$, and find that the difference between the $M=-1$ and $M=+1$ contributions is far more sensitive to changes in $α$ than the longitudinal component.

hep-ph↗

arXiv2019

The $χ_{cJ}$ decay to $ϕK^* \bar K, ϕh_1(1380)$ testing the nature of axial vector meson resonances

We perform a theoretical study of the $χ_{cJ} \to ϕK^* \bar K \to ϕKπ\bar K$ reaction taking into account the $K^* \bar K$ final state interaction, which in the chiral unitary approach is responsible, together with its coupled channels, for the formation of the low lying axial vector mesons, in this case the $h_1(1380)$ given the selection of quantum numbers. Based on this picture we can easily explain why in the $χ_{c0}$ decay the $h_1(1380)$ resonance is not produced, and, in the case of $χ_{c1}$ and $χ_{c2}$ decay, why a dip in the $K^+ π^0 K^-$ mass distribution appears in the 1550-1600 MeV region, that in our picture comes from a destructive interference between the tree level mechanism and the rescattering that generates the $h_1(1380)$ state. Such a dip is not reproduced in pictures where the nominal $h_1(1380)$ signal is added incoherently to a background, which provides support to the picture where the resonance appears from rescattering of vector-pseudoscalar components.

hep-ph↗

arXiv2019

Discerning the two $K_1(1270)$ poles in $D^0\to π^+ V P$ decay

Within the chiral unitary approach, the axial-vector resonance $K_1(1270)$ has been predicted to manifest a two-pole nature. The lowest pole has a mass of 1195 Mev and a width of 246 Mev and couples mostly to $K^*π$, and the highest pole has a mass of 1284 Mev and a width of 146 Mev and couples mostly to $ρK$. We analyze theoretically how this double-pole structure can show up in the $D^0\to π^+ VP$ decays by looking at the vector-pseudoscalar ($VP$) invariant mass distribution for different $VP$ channels, exploiting the fact that each pole couples differently to different $VP$ pairs. We find that the final $\bar K^*π$ and $ρ\bar K$ channels are sensible to the different poles of the $K_1(1270)$ resonance and hence are suitable reactions to analyze experimentally the double pole nature of this resonance.

hep-ph↗

arXiv2019

Prediction of hidden charm strange molecular baryon states with heavy quark spin symmetry

We have studied the meson-baryon $S-$wave interaction, using coupled channels, in the isoscalar hidden-charm strange sector and $J^P = 1/2^-,3/2^-$ and $5/2^-$. We impose constraints of heavy quark spin symmetry in the interaction and obtain the non vanishing matrix elements from an extension of the local hidden gauge approach to the charm sector. The ultraviolet divergences are renormalized using the same meson-baryon-loops regulator previously employed in the non-strange hidden charm sector, where a good reproduction of the properties of the newly discovered pentaquark states is obtained. We obtain five states of $1/2^-$, four of $3/2^-$ and one of $5/2^-$, which could be compared in the near future with forthcoming LHCb experiments. The $5/2^-$, three of the $3/2^-$ and another three of the $1/2^-$ resonances are originated from isoscalar $\bar D^{(*)}Ξ_c^\prime$ and $\bar D^{(*)}Ξ_c^*$ interactions. They should be located just few MeV below the corresponding thresholds (4446, 4513, 4588 and 4655 MeV), and would be SU(3)-siblings of the isospin 1/2 $\bar D^{(*)} Σ_c^{(*)}$ quasi-bound states previously found, and that provided a robust theoretical description of the $P_c(4440)$, $P_c(4457)$ and $P_c(4312)$ LHCb exotic states. The another two $1/2^-$ and $3/2^-$ states obtained in this work are result of the $\bar D^{(*)}Ξ_c-D^{(*)}_sΛ_c$ coupled-channels isoscalar interaction, are significantly broader than the others, with widths of the order of 15 MeV, being $\bar D^{(*)}_sΛ_c$ the dominant decay channel.

hep-ph↗

arXiv2019

Heavy quark spin symmetric molecular states from ${\bar D}^{()}Σ_c^{()}$ and other coupled channels in the light of the recent LHCb pentaquarks

We consider the ${\bar D}^{(*)}Σ_c^{(*)}$ states, together with $J/ψN$ and other coupled channels, and take an interaction consistent with heavy quark spin symmetry, with the dynamical input obtained from an extension of the local hidden gauge approach. By fitting only one parameter to the recent three pentaquark states reported by the LHCb collaboration, we can reproduce the three of them in base to the mass and the width, providing for them the quantum numbers and approximate molecular structure as $1/2^-$ $\bar{D} Σ_c$, $1/2^-$ $\bar{D}^* Σ_c$, and $3/2^-$ $\bar{D}^* Σ_c$, and isospin $I=1/2$. We find another state around 4374 MeV, of $3/2^-$ $\bar{D} Σ_c^*$ structure, for which indications appear in the experimental spectrum. Two other near degenerate states of $1/2^-$ $\bar{D}^* Σ_c^*$ and $3/2^-$ $\bar{D}^* Σ_c^*$ nature are also found around 4520 MeV, which although less clear, are not incompatible with the observed spectrum. In addition, a $5/2^-$ $\bar D^* Σ_c^*$ state at the same energy appears, which however does not couple to $J/ψp$ in $S-$wave, and hence it is not expected to show up in the LHCb experiment.

hep-ph↗

arXiv2019

Theoretical description of the $\boldsymbol{J/ψ\to η(η') h_1(1380)}$, $\boldsymbol{J/ψ\to η(η') h_1(1170)}$ and $\boldsymbol{J/ψ\to π^0 b_1(1235)^0}$ reactions

We have made a study of the $J/ψ\to η' h_1, ηh_1$ (with $h_1$ being $h_1(1170)$ and $h_1(1380)$) and $J/ψ\to π^0 b_1(1235)^0$ assuming the axial vector mesons to be dynamically generated from the pseudoscalar-vector meson interaction. We have taken the needed input from previous studies of the $J/ψ\to ϕππ, ωππ$ reactions. We obtain fair agreement with experimental data and provide an explanation on why the recent experiment on $J/ψ\to η' h_1(1380), h_1(1380) \to K^{*+} K^- +c.c.$ observed in the $K^+ K^- π^0$ mode observes the peak of the $h_1(1380)$ at a higher energy than its nominal mass.

hep-ph↗

arXiv2019

Line shape and $D^{(\ast)}\bar D^{(\ast)}$ probabilities of $ψ(3770)$ from the $e^+e^-\to D\bar D$ reaction

We have performed a calculation of the $D\bar D$, $D\bar D^\ast$, $D^\ast\bar D$, $D^\ast\bar D^\ast$ components in the wave function of the $ψ(3770)$. For this we make use of the $^3P_0$ model to find the coupling of $ψ(3770)$ to these components, that with an elaborate angular momentum algebra can be obtained with only one parameter. Then we use data for the $e^+e^-\to D\bar D$ reaction, from where we determine a form factor needed in the theoretical frame work, as well as other parameters needed to evaluate the meson-meson selfenergy of the $ψ(3770)$. Once this is done we determine the $Z$ probability to still have a vector core and the probability to have the different meson components. We find $Z$ about $80\sim85\%$, and the individual meson-meson components are rather small, providing new empirical information to support the largely $q\bar q$ component of vector mesons, and the $ψ(3770)$ in particular.

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