arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 37 records · Page 2Linked to original sources

arXiv2023

The $T_{c\bar{s}}(2900)$ as a threshold effect from the interaction of the $D^K^$, $D^*_sρ$ channels

We investigate the $D^*K^*$ and $D^*_sρ$ interaction in coupled channels within the hidden gauge formalism. A structure is developed around their thresholds, short of producing a bound state, which leads to a peak in the $D_s^+ π^-$ mass distribution in the $B^0 \to \bar{D}^0 D_s^+ π^-$ decay compatible with the experimental data. We conclude that the interaction between the $D^*K^*$ and $D^*_sρ$ is essential to produce the cusp structure that we associate to the recently seen $T_{c\bar{s}}(2900)$, and that its experimental width is mainly due to the decay width of the $ρ$ meson. The peak obtained together with a smooth background reproduces fairly well the experimental mass distribution observed in the $B_0 \to \bar{D}^0 D_s^+ π^-$ decay.

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arXiv2023

Two states for the $Ξ(1820)$ resonance

We recall that the chiral unitary approach for the interaction of pseudoscalar mesons with the baryons of the decuplet predicts two states for the $Ξ(1820)$ resonance, one with a narrow width and the other one with a large width. We contrast this fact with the recent BESIII measurement of the $K^- Λ$ mass distribution in the $ψ(3686)$ decay to $K^- Λ\barΞ^+ $, which demands a width much larger than the average of the PDG, and show how the consideration of the two $Ξ(1820)$ states provides a natural explanation to this apparent contradiction.

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arXiv2023

The isospin and compositeness of the $T_{cc}(3875)$ state

We perform a fit to the LHCb data on the $T_{cc}(3875)$ state in order to determine its nature. We use a general framework that allows to have the $D^0 D^{*+}$, $D^+ D^{*0}$ components forming a molecular state, as well as a possible nonmolecular state or contributions from missing coupled channels. From the fits to the data we conclude that the state observed is clearly of molecular nature from the $D^0 D^{*+}$, $D^+ D^{*0}$ components and the possible contribution of a nonmolecular state or missing channels is smaller than 3\%, compatible with zero. We also determine that the state has isospin $I=0$ with a minor isospin breaking from the different masses of the channels involved, and the probabilities of the $D^0 D^{*+}$, $D^+ D^{*0}$ channels are of the order of 69\% and 29\% with uncertainties of 1\%. The differences between these probabilities should not be interpreted as a measure of the isospin violation. Due to the short range of the strong interaction where the isospin is manifested, the isospin nature is provided by the couplings of the state found to the $D^0 D^{*+}$, $D^+ D^{*0}$ components, and our results for these couplings indicate that we have an $I=0$ state with a very small isospin breaking. We also find that the potential obtained provides a repulsive interaction in $I=1$, preventing the formation of an $I=1$ state, in agreement with what is observed in the experiment.

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arXiv2023

Inverse problem in femtoscopic correlation functions: The $T_{cc}(3875)^+$ state

We study here the inverse problem of starting from the femtoscopic correlation functions of related channels and analyze them with an efficient tool to extract the maximum information possible on the interaction of the components of these channels, and the existence of possible bound states tied to this interaction. The method is flexible enough to accommodate non-molecular components and the effect of missing channels relevant for the interaction. We apply the method to realistic correlation functions for the $D^{*+}D^0$ and $D^{*0}D^+$ channels derived consistently from the properties of the $T_{cc}(3875)^+$ and find that we can extract the existence of a bound state, its nature as a molecular state of the $D^{*+}D^0$ and $D^{*0}D^+$ channels, the probabilities of each channel, as well as scattering lengths and effective ranges for the channels, together with the size of the source function, all of them with a relatively good precision.

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arXiv2023

Evolution of genuine states to molecular ones: The $T_{cc}(3875)$ case

We address the issue of the compositeness of hadronic states and demonstrate that starting with a genuine state of nonmolecular nature, but which couples to some meson-meson component to be observable in that channel, if that state is blamed for a bound state appearing below the meson-meson threshold it gets dressed with a meson cloud and it becomes pure molecular in the limit case of zero binding. We discuss the issue of the scales, and see that if the genuine state has a mass very close to threshold, the theorem holds, but the molecular probability goes to unity in a very narrow range of energies close to threshold. The conclusion is that the value of the binding does not determine the compositeness of a state. However, in such extreme cases we see that the scattering length gets progressively smaller and the effective range grows indefinitely. In other words, the binding energy does not determine the compositeness of a state, but the additional information of the scattering length and effective range can provide an answer. We also show that the consideration of a direct attractive interaction between the mesons in addition to having a genuine component, increases the compositeness of the state. Explicit calculations are done for the $T_{cc}(3875)$ state, but are easily generalized to any hadronic system.

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arXiv2023

Evolution of compact states to molecular ones with coupled channels: The case of the $X(3872)$

We study the molecular probability of the $X(3872)$ in the $D^0 \bar D^{*0}$ and $D^+ D^{*-}$ channels in several scenarios. One of them assumes that the state is purely due to a genuine nonmolecular component. However, it gets unavoidably dressed by the meson components to the point that in the limit of zero binding of the $D^0 \bar D^{*0}$ component becomes purely molecular. Yet, the small but finite binding allows for a nonmolecular state when the bare mass of the genuine state approaches the $D^0 \bar D^{*0}$ threshold, but, in this case the system develops a small scattering length and a huge effective range for this channel in flagrant disagreement with present values of these magnitudes. Next we discuss the possibility to have hybrid states stemming from the combined effect of a genuine state and a reasonable direct interaction between the meson components, where we find cases in which the scattering length and effective range are still compatible with data, but even then the molecular probability is as big as $95 \%$. Finally, we perform the calculations when the binding stems purely from the direct interaction between the meson-meson components. In summary we conclude, that while present data definitely rule out the possibility of a dominant nonmolecular component, the precise value of the molecular probability requires a more precise determination of the scattering length and effective range of the $D^0 \bar D^{*0}$ channel, as well as the measurement of these magnitudes for the $D^+ D^{*-}$ channel which have not been determined experimentally so far.

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arXiv2023

The $D^+_s \to K^+ π^+ π^-$ reaction and the scalar $f_0(500)$, $f_0(980)$ and $K^*_0 (700)$ resonances

We develop a model to reproduce the mass distributions of pairs of mesons in the Cabibbo-suppressed $D^+_s \to K^+ π^+ π^-$ decay. The largest contributions to the process comes from the $D^+_s \to K^+ ρ^0$ and $D^+_s \to K^{*0} π^+$ decay modes, but the $D^+_s \to K^*_0(1430) π^+$ and $D^+_s \to K^+ f_0(1370)$ modes also play a moderate role and all of them are introduced empirically. Instead, the contribution of the $f_0(500)$, $f_0(980)$ and $K^*_0(700)$ resonances is introduced dynamically by looking at the decay modes at the quark level, hadronizing $q \bar{q}$ pairs to give two mesons, and allowing these mesons to interact to finally produce the $K^+ π^+ π^-$ final state. These last three modes are correlated by means of only one parameter. We obtain a fair reproduction of the experimental data for the three mass distributions as well as the relative weight of the three light scalar mesons, which we see as further support for the nature of these states as dynamically generated from the interaction of pseudoscalar mesons.

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arXiv2023

$B^+$ decay to $K^+ηη$ with ($ηη$) from the $D\bar{D}(3720)$ bound state

We search for a $B$ decay mode where one can find a peak for a $D \bar{D}$ bound state predicted in effective theories and in Lattice QCD calculations, which has also been claimed from some reactions that show an accumulated strength in $D \bar{D}$ production at threshold. We find a good candidate in the $B^+\to K^+ ηη$ reaction, by looking at the $ηη$ mass distribution. The reaction proceeds via a first step in which one has the $B^+\to D_s^{*+} \bar{D}^0$ reaction followed by $D_s^{*+}$ decay to $D^0 K^+$ and a posterior fusion of $D^0 \bar{D}^0$ to $ηη$, implemented trough a triangle diagram that allows the $D^0 \bar{D}^0$ to be virtual and produce the bound state. The choice of $ηη$ to see the peak is based on results of calculations that find the $ηη$ among the light pseudoscalar channels with stronger coupling to the $D \bar{D}$ bound state. We find a neat peak around the predicted mass of that state in the $ηη$ mass distribution, with an integrated branching ratio for $B^+\to K^+$ ($D\bar{D}$, bound) ; ($D\bar{D}$, bound) $\to ηη$ of the order of $1.5 \times 10^{-4}$, a large number for hadronic $B$ decays, which should motivate its experimental search.

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arXiv2023

Femtoscopic correlation function for the $T_{cc}(3875)^+$ state

We have conducted a study of the femtoscopic correlation functions for the $D^0D^{*+}$ and $D^+D^{*0}$ channels that build the $T_{cc}$ state. We develop a formalism that allows us to factorize the scattering amplitudes outside the integrals in the formulas, and the integrals involve the range of the strong interaction explicitly. For a source of size of 1 fm, we find values for the correlation functions of the $D^0 D^{*+}$ and $D^+D^{*0}$ channels at the origin around 30 and 2.5, respectively, and we see these observables converging to unity already for relative momenta of the order of 200 MeV. We conduct tests to see the relevance of the different contributions to the correlation function and find that it mostly provides information on the scattering length, since the presence of the source function in the correlation function introduces an effective cut in the loop integrals that makes them quite insensitive to the range of the interaction.

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arXiv2023

Shedding light on the $ X(3930) $ and $ X(3960) $ states with the $B^- \to K^- J/ψω$ reaction

We have studied the contribution of the state $X(3930)$, coming from the interaction of the $D \overline{D}$ and $D^{+}_s D^{-}_s$ channels, to the $B^- \to K^- J/ψω$ decay. The purpose of this work is to offer a complementary tool to see if the $X(3930)$ state observed in the $D^+ D^-$ channel is the same or not as the $X(3960)$ resonance claimed by the LHCb collaboration from a peak in the $D^{+}_s D^{-}_s$ mass distribution around threshold. We present results for what we expect in the $J/ψω$ mass distribution in the $B^- \to K^- J/ψω$ decay and conclude that a clear signal should be seen around $3930\,\rm MeV$. At the same time, finding no extra resonance signal at $3960\,\rm MeV$ would be a clear indication that there is not a new state at $3960\,\rm MeV$, supporting the hypothesis that the near-threshold peaking structure peak in the $D^{+}_s D^{-}_s$ mass distribution is only a manifestation of a resonance below threshold.

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arXiv2023

Molecular states of $ D^* D^* \bar{K}^*$ nature

We study the interaction of two $ D^* $ and a $\bar{K}^{*}$ by using the Fixed Center Approximation to the Faddeev equations to search for bound states of the three body system. Since the $ D^* D^* $ interaction is attractive and gives a bound state, and so is the case of the $D^* \bar{K}^{*}$ interaction, where the $J^{P}=0^{+}$ bound state is identified with the $X_0 (2900)$, the $ D^* D^* \bar{K}^{*}$ system leads to manifestly exotic bound states with $ccs$ open quarks. We obtain bound states of isospin $I=1/2$, negative parity and total spin $J=0,1,2$. For $J=0$ we obtain one state, and for $J=1,2$ we obtain two states in each case. The binding energies range from $56$ MeV to $151$ MeV and the widths from $80$ MeV to $100$ MeV.

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arXiv2023

Theoretical study of the $γd \to π^0ηd$ reaction

We have done a theoretical study of the $γd \to π^0 ηd$ reaction starting with a realistic model for the $γN \to π^0 ηN$ reaction that reproduces cross sections and polarization observables at low energies and involves the $γN \to Δ(1700)\to ηΔ(1232) \to ηπ^0 N$ process. For the coherent reaction in the deuteron we considered the impulse approximation together with the rescattering of the pions and the $η$ on a different nucleon than the one where they are produced. We found this second mechanism very important since it helps share between two nucleons the otherwise large momentum transfer of the reaction. Other contributions to the $γd\toπ^0ηd$ reaction, involving the $γN\to π^\pmπ^0 N^\prime$ process, followed by the rescattering of the $π^\pm$ with another nucleon to give $η$ and a nucleon, have also been included. We find a natural explanation, tied to the dynamics of our model, for the shift of the $η-d$ mass distribution to lower invariant masses, and of the $π^0-d$ mass distribution to larger invariant masses, compared to a phase space calculation. We also study theoretical uncertainties related to the large momenta of the deuteron wave function involved in the process as well as to the couplings present in the model. Striking differences are found with the experimental angular distribution and further theoretical investigations might be necessary.

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arXiv2023

Repercussion of the $a_0(1710)$ [$a_0(1817)$] resonance and future developments

In this paper, we discuss the significance and prospect for the newly discovered a0(1710)[a0(1817)] resonance state at BESIII experiment, in which they reported the observation of a scalar meson of spin-parity $J^P=0^+$ with isospin $I=1$, branded as $a_0(1817)$. This state may be the same particle as the $a_0(1710)$ observed by the BaBar experiment earlier. As early as 2008, we found that f0(1710) can be regarded as a $K^* \bar{K}^*$ molecular state based on the chiral unitary theory, and there is a partner state $a_0(1710)$ with an isospin $I=1$. Our theoretical prediction based on this picture is in good agreement with the latest BESIII data, which further supports the molecular state picture of $a_0(1710)[a_0(1817)]$. If it is indeed the isospin partner state of $f_0(1710)$, this would rule out $f_0(1710)$ as a glueball candidate. This paper briefly reviews the relevant theoretical studies and suggests new experiments to further examine the nature of $a_0(1710)[a_0(1817)]$.

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arXiv2023

Sequential single pion production explaining the dibaryon "$d^*(2380)$" peak

We study the two step sequential one pion production mechanism, $np(I=0)\to π^-pp$, followed by the fusion reaction $pp\to π^+d$, in order to describe the $np\to π^+π^-d$ reaction with $π^+π^-$ in $I=0$, where a narrow peak, so far identified with a "$d(2380)$" dibaryon, has been observed. We find that the second step $pp\to π^+d$ is driven by a triangle singularity that determines the position of the peak of the reaction and the large strength of the cross section. The combined cross section of these two mechanisms produce a narrow peak with the position, width and strength compatible with the experimental observation within the approximations done. This novel interpretation of the peak without invoking a dibaryon explains why the peak is not observed in other reactions where it has been searched for.

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arXiv2022

$D_1(2420)$ and its interactions with a kaon: open charm states with strangeness

In this work we present an attempt to describe the $X_1(2900)$ found by the LHCb collaboration, in the experimental data on the invariant mass spectrum of $ D^-K^+$, as a three-meson molecular state of the $Kρ\bar D$ system. We discuss that the interactions in all the subsystems are attractive in nature, with the $ρ\bar D$ interaction generating $\bar D_1(2420)$ and the $K ρ$ resonating as $K_1(1270)$. We find that the system can form a three-body state but with a mass higher than that of $X_1(2900)$. We investigate the $K ρD$ system too, finding that the three-body dynamics generates an isoscalar state, which can be related to $D_{s1}^*(2860)$, and an exotic isovector state. This latter state has a mass similar to that of the $X_0(2900)$ and $X_1(2900)$ states found by LHCb, but a very small width ($\sim 7.4 \pm 0.9$ MeV) and necessarily requires more than two quarks to describe its properties. We hope that our findings will encourage experimental investigations of the isovector $K ρD$ state. Finally, in the pursuit of finding a description for $X_1(2900)$, we study the $π\bar K^* D^*$ system where $ \bar K^*D^*$ forms $0^+$, $1^+$ and $2^+$ states. We do not find a state which can be associated with $X_1(2900)$.

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arXiv2022

Studying the process $γd \to π^0ηd$

In these proceedings we present our recent results on the study of the process $γd \to π^0 ηd$, where the existence of a dibaryon in the $ηd$ invariant mass distribution has been recently claimed. As we will show, many of the relevant aspects observed in the experiment, as the shift of the $ηd$ and $πd$ invariant mass distributions with respect to phase space can be described with our model, where no dibaryon is formed. Instead, we consider the interaction of the $γ$ with the nucleons forming the deuteron to proceed through $γN \to Δ(1700)\to ηΔ(1232) \to ηπ^0 N$, followed by the rescattering of the $π$ and $η$ with the other nucleon of the deuteron. Theoretical uncertainties related to different parameterizations of the deuteron wave function are investigated

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arXiv2022

Exotic states with triple charm

In this work we investigate the possibility of the formation of states from the dynamics involved in the $D^*D^*D^*$ system by considering that two $D^*$'s generate a $J^P=1^+$ bound state, with isospin 0, which has been predicted in an earlier theoretical work. We solve the Faddeev equations for this system within the fixed center approximation and find the existence of $J^P=0^-$, $1^-$ and $2^-$ states with charm $3$, isospin $1/2$, masses $\sim 6000$ MeV, which are manifestly exotic hadrons, i.e., with a multiquark inner structure.

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arXiv2022

The $T_{c\bar{s}}(2900)$ as a threshold effect from the interaction of the $D^K^$, $D^*_sρ$ channels

We look at the mass distribution of the $D_s^+ π^-$ in the $B^0 \to \bar{D}^0 D_s^+ π^-$ decay, where a peak has been observed in the region of the $D^*_s ρ$, $D^* K^*$ thresholds. By creating these two channels together with a $\bar{D}^0$ in $B^0$ decay and letting them interact as coupled channels, we obtain a structure around their thresholds, short of producing a bound state, which leads to a peak in the $D_s^+ π^-$ mass distribution in the $B^0 \to \bar{D}^0 D_s^+ π^-$ decay. We conclude that the interaction between the $D^*K^*$ and $D^*_sρ$ is essential to produce the cusp structure that we associate to the recently seen $T_{c\bar{s}}(2900)$, and that its experimental width is mainly due to the decay width of the $ρ$ meson. The peak obtained together with a smooth background reproduces fairly well the experimental mass distribution observed in the $B_0 \to \bar{D}^0 D_s^+ π^-$ decay.

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