arXiv subjects

Eulogio Oset

Publications and source records attributed to Eulogio Oset.

At least 73 records · Page 4Linked to original sources

arXiv2024

A note on the tensor and vector exchange contributions to $K \bar K \to K \bar K, D \bar D \to D \bar D $ and $π^+ π^-\to π^+ π^-$ reactions

In this note we study the tensor and vector exchange contributions to the elastic reactions involving the pseudoscalars mesons $π^+ π^-$, $K^{+}K^{-}$ and $D^{+}D^{-}$. In the case of the tensor-exchange contributions we assume that an intermediate tensor $f_2(1270)$ is dynamically generated from the interaction of two virtual $ρ$ mesons, with the use of a pole approximation. The calculation of the two-loop amplitude is facilitated since the triangle loops can be factorized and computed separately. The results show very small contributions coming from the tensor-exchange mechanisms when compared with those from the vector-exchange processes. We compare our results for $ππ$ and $K\bar{K}$ scattering with those obtained in other works where the $f_2(1270)$ is considered as an ordinary $q\bar{q}$ meson. Our picture provides a smaller contribution but of similar order of magnitude for pion scattering and stabilizes the results in the case of $K\bar{K}$, allowing us to make estimates for $D\bar{D}$ scattering.

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arXiv2024

Correlation functions for the $N^*(1535)$ and the inverse problem

The $N^*(1535)$ can be dynamically generated in the chiral unitary approach with the coupled channels, $K^0 Σ^+, K^+ Σ^0, K^+ Λ$ and $ηp$. In this work we evaluate the correlation functions for every channel and face the inverse problem. Assuming the correlation functions to correspond to real measurements, we conduct a fit to the data within a general framework in order to extract the information contained in these correlation functions. The bootstrap method is used to determine the uncertainties of the different observables, and we find that, assuming errors of the same order than in present measurements of correlation functions, one can determine the scattering length and effective range of all channels with a very good accuracy. Most remarkable is the fact that the method predicts the existence of a bound state of isospin $\frac{1}{2}$ nature around the mass of the $N^*(1535)$ with an accuracy of $6\; \rm MeV$. These results should encourage the actual measurement of these correlation functions (only the $K^+ Λ$ one is measured so far), which can shed valuable light on the relationship of the $ N^*(1535)$ state to these coupled channels, a subject of continuous debate.

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arXiv2024

$D^+ \to K_s^0 π^+ η$ reaction and $a_0(980)^+$

We study the $D^+ \to \bar K^0 π^+ η$ reaction where the $a_0(980)$ excitation plays a dominant role. We consider mechanisms of external and internal emission at the quark level, hadronize the $q \bar q$ components into two mesons and allow these mesons to undergo final state interaction where the $a_0(980)$ state is generated. While the $a_0(980)$ production is the dominant term, we also find other terms in the reaction that interfere with this production mode and, through interference with it, lead to a shape of the $a_0(980)$ significantly different from the one observed in other experiments, with an apparently much larger width.

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arXiv2024

$J/ψ$ decays into $ω(ϕ) f_1(1285)$ and $ω(ϕ) \,''f_1(1420)''$

We perform a theoretical study of the $J/ψ\to ω(ϕ) K^* \bar{K} + c.c. \to ω(ϕ) K^0 π^+ K^-$ reactions with the assumption that the $f_1(1285)$ is dynamically generated from a single channel $K^* \bar{K} + c.c$ interaction in the chiral unitary approach. Two peaks in the $K^0 π^+ K^-$ invariant mass distribution are observed, one clear peak locates at the $f_1(1285)$ nominal mass, the other peak locates at around $1420\; \rm MeV$ with about $70 \;\rm MeV$ width. We conclude that the former peak is associated with the $f_1(1285)$ and the latter peak is not a genuine resonance but a manifestation of the kinematic effect in the higher energy region caused by the $K^* \bar{K} + c.c.$ decay mode of the $f_1(1285)$.

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arXiv2024

On the molecular nature of the $Ω_c(3120)$ and its analogy with the $Ω(2012)$

We make a study of the $Ω_c(3120)$, one of the five $Ω_c$ states observed by the LHCb collaboration, which is well reproduced as a molecular state from the $Ξ^*_c \bar K$ and $Ω^*_c η$ channels mostly. The state with $J^P = 3/2^-$ decays to $Ξ_c \bar K$ in $D$-wave and we include this decay channel in our approach, as well as the effect of the $Ξ^*_c$ width. With all these ingredients, we determine the fraction of the $Ω_c(3120)$ width that goes into $Ξ_c π\bar K$, which could be a measure of the $Ξ^*_c \bar K$ molecular component, but due to a relatively big binding, compared to its analogous $Ω(2012)$ state, we find only a small fraction of about 3%, which makes this measurement difficult with present statistics. As an alternative, we evaluate the scattering length and effective range of the $Ξ^*_c \bar K$ and $Ω^*_c η$ channels which together with the binding and width of the $Ω_c(3120)$ state, could give us an answer to the issue of the compositeness of this state when these magnitudes are determined experimentally, something feasible nowadays, for instance, measuring correlation functions.

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arXiv2023

Model independent analysis of femtoscopic correlation functions: An application to the $D_{s0}^*(2317)$

We face the inverse problem of obtaining the interaction between coupled channels from the correlation functions of these channels. We apply the method to the interaction of the $D^0 K^+$, $D^+ K^0$, and $D^+_s η$ channels, from where the $D^*_{s0}(2317)$ state emerges. We use synthetic data extracted from an interaction model based on the local hidden gauge approach and find that the inverse problem can determine the existence of a bound state of the system with a precision of about 20 MeV. At the same time, we can determine the isospin nature of the bound state and its compositeness in terms of the channels. Furthermore, we evaluate the scattering length and effective range of all three channels, as well as the couplings of the bound state found to all the components. Lastly, the size parameter of the source function, $R$, which in principle should be a magnitude provided by the experimental teams, can be obtained from a fit to the data with relatively high accuracy. These findings show the value of the correlation function to learn about the meson-meson interaction for systems which are difficult to access in other present facilities.

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arXiv2023

$J/ψ$ decay to $ ϕ,ω, K^{0}$ plus $f_0(1370)$, $f_0(1710)$, $K_0^(1430)$, $f_2(1270)$, $f'_2(1525)$ and $K_2^*(1430)$: role of the $D$-wave for tensor production

We reassess the decay of the $J/ψ$ into an $ω, ϕ, K^{*0}$ and one of the $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f'_2(1525)$, $K_0^*(1430)$ and $K_2^*(1430)$ resonances. We benefit from previous works that considered this reaction as a $J/ψ$ decay into three vector mesons, with a scalar or tensor resonance being formed from the interaction of two of these vectors. The novelty here with respect to former studies is the investigation of the relation between the scalar meson and tensor productions for the first time. To this end, the spin structure of the four vectors present in the production vertex is analyzed, and the $D$-wave mechanism in the tensor production is included. Then, beyond the ratios studied previously involving scalar states and tensor states independently, new ratios relating the scalar and tensor meson productions are estimated. Our results suggest that the $D$-wave mechanism of tensor production assumes a relevant contribution. New experimental data reporting the angular distributions of these processes will be important for checking this conclusion.

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arXiv2023

Role of $f_0(980)$ and $a_0(980)$ in the $B^- \to π^- K^+ K^- $ and $B^- \to π^- K^0 \bar K^0 $ reactions

In this work we study the role of the $f_0(980)$ and $a_0(980)$ resonances in the low $ K ^{+} K^{-} $ and $K^0 \bar K^0 $ invariant-mass region of the $B^- \to π^- K^+ K^- $ and $B^- \to π^- K^0 \bar K^0 $ reactions. The amplitudes are calculated by using the chiral unitary $\rm SU(3)$ formalism, in which these two resonances are dynamically generated from the unitary pseudocalar-pseudoscalar coupled-channel approach. The amplitudes are then used as input in the evaluation of the mass distributions with respect to the $ K^{+}K^{-} $ and $ K^{0}\bar K^{0} $ invariant-masses, where the contributions coming from the $I=0$ and $I=1$ components are explicitly assessed. Furthermore, the contribution of the $ K^{\ast }(892)^0 K^- $ production and its influence on the $ π^{-} K^+ $ and $ K^{+} K^- $ systems are also evaluated, showing that there is no significant strength for small $ K^{+} K^- $ invariant mass. Lastly, the final distributions of $ M_{\rm inv}^2( K^{\pm}K^{\mp} ) $ for the $B^{\mp} \to π^{\mp} K^{\pm}K^{\mp} $ reactions are estimated and compared with the LHCb data. Our results indicate that the $I=0$ component tied to the $f_0(980)$ excitation generates the dominant contribution in the range of low $ K ^{+} K^{-} $ invariant-mass.

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arXiv2023

Traces of the new $a_0(1780)$ resonance in the $J/ψ\to ϕK^+K^-(K^0\bar{K}^0)$ reaction

We study the $J/ψ\to ϕK \bar K$ decay, looking for differences in the production rates of $K^+ K^-$ or $K^0 \bar K^0$ in the region of 1700-1800 MeV, where two resonances appear dynamically generated from the vector-vector interaction. Two resonances are known experimentally in that region, the $f_0(1710)$ and a new resonance reported by the BABAR and BESIII collaborations. The $K \bar K$ should be produced with $I=0$ in that reaction, but due to the different $K^{*0}$ and $K^{*+}$ masses some isospin violation appears. Yet, due to the large width of the $K^*$, the violation obtained is very small and the rates of $K^+ K^-$ or $K^0 \bar K^0$ production are equal within $5\%$. However, we also find that due to the step needed to convert two vectors into $K \bar K$, a shape can appear in the $K \bar K$ mass distribution that can mimic the $a_0$ production around the $K^* \bar K^*$ threshold, and is simply a threshold effect.

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arXiv2023

A new look at the $P_{cs}$ states from a molecular perspective

We have a look at the $P_{cs}$ states generated from the interaction of $\bar D^{(*)} Ξ^{(\prime*)}_c$ coupled channels. We consider the blocks of pseudoscalar-baryon $({\frac12}^+, {\frac32}^+)$ and vector-baryon $({\frac12}^+, {\frac32}^+)$, and find $10$ resonant states coupling mostly to $\bar D Ξ_c, \bar D^* Ξ_c,\bar D Ξ'_c, \bar D^* Ξ'_c,\bar D Ξ^*_c$ and $\bar D^* Ξ^*_c$. A novel aspect of the work is the realization that the $\bar D Ξ_c,\bar D_sΛ_c$ or $\bar D^* Ξ_c,\bar D^*_sΛ_c$ channels, with a strong transition potential, collaborate to produce a larger attraction than the corresponding states $\bar D Σ_c,\bar DΛ_c$ or $\bar D^* Σ_c,\bar D^*Λ_c$ appearing in the generation of the strangenessless $P_{c}$ states, since in the latter case the transition potential between those channels is zero. The extra attraction obtained in the $\bar D Ξ_c,\bar D^* Ξ_c$ pairs preclude the association of these channels to the $P_{cs}(4338)$ and $P_{cs}(4459)$ states respectively. Then we find a natural association of the $P_{cs}(4338)$ state coupling mostly to $\bar D^* Ξ_c$ while the $P_{cs}(4459)$ is associated to the state found that couples mostly to $\bar D Ξ'_c$. Four more states appear, like in other molecular pictures, and some of the states are degenerate in spin. Counting different spin states we find $10$ states, which we hope can be observed in the near future.

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arXiv2022

Molecular $Ω_{cc}$ , $Ω_{bb}$ and $Ω_{bc}$ states

We study the interaction of meson-baryon coupled channels carrying quantum numbers of $Ω_{cc}$ , $Ω_{bb}$ and $Ω_{bc}$ presently under investigation by the LHCb collaboration. The interaction is obtained from an extension of the local hidden gauge approach to the heavy quark sector that has proved to provide accurate results compared to experiment in the case of $Ω_{c}$ , $Ξ_{c}$ states and pentaquarks, $P_c$ and $P_{cs}$. We obtain many bound states, with small decay widths within the space of the chosen coupled channels. The spin-parity of the states are $J^P={\frac{1}{2}}^-$ for coupled channels of pseudoscalar-baryon (${\frac{1}{2}}^+$), $J^P={\frac{3}{2}}^-$ for the case of pseudoscalar-baryon (${\frac{3}{2}}^+$), $J^P={\frac{1}{2}}^-,{\frac{3}{2}}^-$ for the case of vector-baryon (${\frac{1}{2}}^+$) and $J^P={\frac{1}{2}}^-,{\frac{3}{2}}^-,{\frac{5}{2}}^-$ for the vector-baryon (${\frac{3}{2}}^+$) channels. We look for poles of the states and evaluate the couplings to the different channels. The couplings obtained for the open channels can serve as a guide to see in which reaction the obtained states are more likely to be observed.

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arXiv2022

Interpretation of the $Ω_c \to π^+ Ω(2012) \to π^+(\bar{K} Ξ)$ relative to $Ω_c \to π^+\bar{K} Ξ$ from the $Ω(2012)$ molecular perspective

We present a mechanism for $Ω_c \to π^+ Ω(2012)$ production through an external emission Cabibbo favored weak decay mode, where the $Ω(2012)$ is dynamically generated from the interaction of $\bar{K}Ξ^*(1530)$, $ηΩ$, with $\bar{K}Ξ$ as the main decay channel. The $Ω(2012)$ decays later to $\bar{K}Ξ$ in this picture, with results compatible with Belle data. The picture has as a consequence that one can evaluate the direct decay $Ω_c^0 \to π^+K^- Ξ^0$ and the decay $Ω_c^0 \to π^+\bar{K} Ξ^*$, $π^+ηΩ$ with direct coupling of $\bar{K}Ξ^*$ and $ηΩ$ to $K^- Ξ^0$. We show that, within uncertainties and using data from a recent Belle measurement, all these three channels account for about (12-20)\% of the total $Ω_c \to π^+K^- Ξ^0$ decay rate. The consistency of the molecular picture with all the data is established by showing that $Ω_c \to Ξ^0 \bar{K}^{*0} \to Ξ^0K^- π^+$ together with $Ω_c \to π^+ Ω^* \to π^+K^- Ξ^0 $ account for about 85\% of the total $Ω_c \to π^+K^- Ξ^0 $.

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arXiv2022

$Z_{cs}$ states from the $D^{}_s \bar D^$ and $J/ψK^*$ coupled channels: Signal in $B^+ \to J/ψϕK^+$ decay

We study the $D^{*}_s \bar D^*$ system in connection with the $J/ψK^*$ in coupled channels and observe that, within reasonable values of the cut-off used to regularize the loops, the system does not develop a bound state. However, the $J^P = 2^+$ channel has enough attraction to create a strong cusp structure that shows up in the $J/ψK^+$ invariant mass distribution in the $B^+ \to J/ψϕK^+$ decay at the $D^*_s \bar D^*$ threshold. Such structure is visible in the experimental $B^+ \to J/ψϕK^+$ and $\bar B^0 \to J/ψK^+ K^-$ decays, with small statistics, and our results should stimulate further measurements around this region, given the fact that cusp effects provide as valuable information on hadron dynamics as resonances themselves.

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arXiv2021

Triangle singularity mechanism for the $pp \to π^+ d$ fusion reaction

We develop a model for the $pp \to π^+ d$ reaction based on the $pp \to Δ(1232) N$ transition followed by $Δ(1232) \to πN'$ decay and posterior fusion of $N N'$ to give the deuteron. We show that the triangle diagram depicting this process develops a triangle singularity leading to a large cross section of this reaction compared to ordinary fusion reactions. The results of the calculation also show that the process is largely dominated by the $pp$ system in $L=2, S=0$, which transfers $J=2$ to the final $π^+ d$ system. This feature is shown to be well suited to provide $L=2,S=1$, $J^\mathrm{tot}=3$ for $np$ in the $np(I=0) \to π^- pp$ followed by $pp \to π^+ d$ reaction, which has been proposed recently, as a means of describing the so far assumed dibaryon $d^*(2380)$ peak.

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arXiv2021

$Λ(1405)$ mediated triangle singularity in the $K^-d\to pΣ^-$ reaction

We study for the first time the $pΣ^-\to K^-d$ and $K^-d\to pΣ^-$ reactions close to threshold and show that they are driven by a triangle mechanism, with the $Λ(1405)$, a proton and a neutron as intermediate states, which develops a triangle singularity close to the $\bar{K}d$ threshold. We find that a mechanism involving virtual pion exchange and the $K^-p\toπ^+Σ^-$ amplitude dominates over another one involving kaon exchange and the $K^-p\to K^-p$ amplitude. Moreover, of the two $Λ(1405)$ states, the one with higher mass around $1420$ MeV, gives the largest contribution to the process. We show that the cross section, well within measurable range, is very sensitive to different models that, while reproducing $\bar{K}N$ observables above threshold, provide different extrapolations of the $\bar{K}N$ amplitudes below threshold. The observables of this reaction will provide new constraints on the theoretical models, leading to more reliable extrapolations of the $\bar{K}N$ amplitudes below threshold and to more accurate predictions of the $Λ(1405)$ state of lower mass.

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arXiv2021

Analysis of the $ \boldsymbol{γγ\to D\bar D}$ reaction and the $D\bar{D}$ bound state

In this work, we investigate the reaction of $γγ\to D\bar{D}$, taking into account the s-wave $D\bar{D}$ final state interaction. By fitting to the $D\bar{D}$ invariant mass distributions measured by the Belle and BaBar Collaborations, we obtain a good reproduction of the data by means of a $D\bar{D}$ amplitude that produces a bound $D\bar{D}$ state with $I=0$ close to threshold. The error bands of the fits indicate, however, that more precise data on this reaction are needed to be more assertive about the position and width of such state.

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arXiv2021

The $Z_{cs}(3985)$ as a threshold effect from the $\bar D_s^* D + \bar D_s D^*$ interaction

We study the $e^+ e^- \to K^+ ( D_s^{*-} D^0 + D_s^- D^{*0})$ reaction recently measured at BESIII, from where a new $Z_{cs}$ state has been reported. We study the interaction of $\bar D_s D^*$ with the coupled channels $J/ψK^-$, $K^{*-} η_c$, $D_s^- D^{*0}$, $D_s^{*-} D^0$ by means of an extension to the charm sector of the local hidden gauge approach. We find that the $D_s^- D^{*0}+ D_s^{*-} D^0$ combination couples to $J/ψK^-$ and $K^{*-} η_c$, but the $D_s^- D^{*0}- D_s^{*-} D^0$ combination does not. The coupled channels help to build up strength in the $D_s^- D^{*0}+ D_s^{*-} D^0$ diagonal scattering matrix close to threshold and, although the interaction is not strong enough to produce a bound state or resonance, it is sufficient to produce a large accumulation of strength at the $\bar D_s D^*$ threshold in the $e^+ e^- \to K^+ ( D_s^{*-} D^0 + D_s^- D^{*0})$ reaction in agreement with experiment.

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arXiv2021

Combined theoretical study of the $D^+ \to π^+ ηη$ and $D^+ \to π^+ π^0 η$ reactions

We study the $D^+ \to π^+ ηη$ and $D^+ \to π^+ π^0 η$ reactions, which are single Cabibbo suppressed and can proceed both through internal and external emission. The primary mechanisms at quark level are considered, followed by hadronization to produce three mesons in the $D^+$ decay, and after that the final state interaction of these mesons leads to the production of the $a_0(980)$ resonance, seen in the $π^+ η$, $π^0 η$ mass distributions. The theory has three unknown parameters to determine the shape of the distributions and the ratio between the $D^+ \to π^+ ηη$ and $D^+ \to π^+ π^0 η$ rates. This ratio restricts much the sets of parameters but there is still much freedom leading to different shapes in the mass distributions. We call for a measurement of these mass distributions that will settle the reaction mechanism, while at the same time provide relevant information on the way that the $a_0(980)$ resonance is produced in the reactions.

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