arXiv subjects

Eulogio Oset

Publications and source records attributed to Eulogio Oset.

At least 91 records · Page 5Linked to original sources

arXiv2021

Analysis of the $ \boldsymbol{e^+ e^- \to J/ψD\bar D}$ reaction close to the threshold concerning claims of a $χ_{c0}(2P)$ state

We analyze the $D\bar{D}$ mass distribution from a recent Belle experiment on the $e^+e^- \to J/ψD\bar{D}$ reaction, and show that the mass distribution divided by phase space does not have a clear peak above the $D\bar{D}$ threshold that justifies the experimental claim of a $χ_{c0}(2P)$ state from those data. Then we use a unitary formalism with coupled channels $D^+D^-$, $D^0\bar{D}^0$, $D_s\bar{D}_s$, and $ηη$, with some of the interactions taken from a theoretical model, and use the data to fix other parameters. We then show that, given the poor quality of the data, we can get different fits leading to very different $D\bar{D}$ amplitudes, some of them supporting a $D\bar{D}$ bound state and others not. The main conclusion is that the claim for the $χ_{c0}(2P)$ state, already included in the PDG, is premature, but refined data can provide very valuable information on the $D\bar{D}$ scattering amplitude. As side effects, we warn about the use of a Breit-Wigner amplitude parameterization close to threshold, and show that the $D_s\bar{D}_s$ channel plays an important role in this reaction.

hep-ph↗

arXiv2020

The role of $X(4140)$ and $X(4160)$ in the reactions of $B^+ \to J/ψϕK^+$

We have studied the $J/ψϕ$ mass distribution of the process $B^+\to J/ψϕK^+$ from the threshold to about 4250 MeV, by considering the contribution of the $X(4140)$ with a narrow width, together with the $X(4160)$ state. Our results show that the cusp structure at the $D^*_s\bar{D}^*_s$ threshold is tied to the molecular nature of the $X(4160)$ state.

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arXiv2020

Theoretical study of the $D^0 \to K^- π^+ η$ reaction

We develop a model to study the $D^0 \to K^- π^+ η$ weak decay, starting with the color favored external emission and Cabibbo favored mode at the quark level. A less favored internal emission decay mode is also studied as a source of small corrections. Some pairs of quarks are allowed to hadronize producing two pseudoscalar mesons, which posteriorly are allowed to interact to finally provide the $K^- π^+ η$ state. The chiral unitary approach is used to take into account the final state interaction of pairs of mesons, which has as a consequence the production of the $κ$ ($K^*_0(700)$) and the $a_0(980)$ resonances, very well visible in the invariant mass distributions. We also introduce the $\bar{K}^{*0} η$ production in a phenomenological way and show that the $s$-wave pseudoscalar interaction together with this vector excitation mode are sufficient to provide a fair reproduction of the experimental data. The agreement with the data, in particular the relative weight of the $a_0(980)$ to the $κ$ excitation, provides extra support to the picture used, in which these two resonances are a consequence of the interaction of pseudoscalar mesons and not ordinary $q \bar{q}$ mesons.

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arXiv2020

Triangle singularity in $B^-\to K^-X(3872);X\to π^0π^+π^-$ and the X(3872) mass

We evaluate the contribution to the $X(3872)$ width from a triangle mechanism in which the $X$ decays into $D^{*0}\bar{D}^0 -cc$, then the $D^{*0} (\bar{D}^{*0})$ decays into $D^0 π^0$ ($\bar{D}^0 π^0$) and the $D^0 \bar{D}^0$ fuse to produce $π^+ π^-$. This mechanism produces an asymmetric peak from a triangle singularity in the $π^+ π^-$ invariant mass with a shape very sensitive to the $X$ mass. We evaluate the branching ratios for a reaction where this effect can be seen in the $B^- \to K^- π^0 π^+ π^-$ reaction and show that the determination of the peak in the invariant mass distribution of $π^+ π^-$ is all that is needed to determine the $X$ mass. Given the present uncertainties in the $X$ mass, which do not allow to know whether the $D^{*0} \bar{D}^0$ state is bound or not, measurements like the one suggested here should be most welcome to clarify this issue.

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arXiv2020

Molecular picture for the $Ω(2012)$ revisited

We conduct a study of the interaction of the $\bar K Ξ^*$, $ηΩ$($s$-wave) and $\bar K Ξ$($d$-wave) channels within a coupled channel unitary approach where the transition potential between the $\bar K Ξ^*$ and $ηΩ$ channels is obtained from chiral Lagrangians. The transition potential between $\bar K Ξ^*$, $ηΩ$ and $\bar K Ξ$ is taken in terms of free parameters, which together with a cut off to regularize the meson-baryon loops are fitted to the $Ω(2012)$ data. We find that all data including the recent Belle experiment on $Γ_{Ω^* \to π\bar K Ξ}/ Γ_{Ω^* \to \bar K Ξ}$, are compatible with the molecular picture stemming from meson baryon interaction of these channels.

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arXiv2020

Searching for a $D \bar D$ bound state with the $ψ(3770) \to γD^0 \bar D^0$ decay

We perform a calculation of the mass distribution in the $ψ(3770) \to γD \bar D$ decay, studying both the $D^+ D^- $ and $D^0 \bar D^0 $ decays. The electromagnetic interaction is such that the tree level amplitude is null for the neutral channel, which leaves the $ψ(3770) \to γD^0 \bar D^0$ proceeding through a loop involving the $D^+ D^- \to D^0 \bar D^0$ scattering amplitude. We use the results for this amplitude of a theoretical model that predicts a $D \bar D$ bound state and find a $D^0 \bar D^0 $ mass distribution in the decay drastically different than phase space. The rates obtained are relatively large and the experiment is easily feasible in the present BESIII facility. The performance of this experiment could provide an answer to the issue of this much searched for state, which is the analogue of the $f_0(980)$ resonance.

hep-ph↗

arXiv2020

Triangle singularity in the $B^-\to K^-π^0X(3872)$ reaction and sensitivity to the $X(3872)$ mass

We have done a study of the $B^- \to K^- π^0 X(3872)$ reaction by means of a triangle mechanism via the chain of reactions: $B^- \to K^- D^{*0}\bar D^{*0}$; $D^{*0} \to π^0 D^0$; $D^0\bar D^{*0}\to X(3872)$. We show that this mechanism generates a triangle singularity in the $π^0 X(3872)$ invariant mass for a very narrow window of the $X(3872)$ mass, around the present measured values, and show that the peak positions and the shape of the mass distributions are sensitive to the $X(3872)$ mass, such that a measurement of the reaction can serve to improve on the present values of this mass. In particular, we point out that the $X(3872)$ mass relative to the $D^0\bar D^{*0}$ threshold may be extracted from the asymmetry of the $π^0X$ line shape.

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arXiv2020

$Υ(nl)$ decay into $ B^{()} \bar B^{()}$

We have evaluated the decay modes of the $Υ(4s), Υ(3d), Υ(5s), Υ(6s)$ states into $B\bar B, B\bar B^*+c.c., B^* \bar B^*, B_s \bar B_s, B_s \bar B^*_s +c.c., B^*_s \bar B_s^* $ using the $^3P_0$ model to hadronize the $b\bar b$ vector seed, fitting some parameters to the data. We observe that the $Υ(4s)$ state has an abnormally large amount of meson-meson components in the wave function, while the other states are largely $b\bar b$. We predict branching ratios for the different decay channels which can be contrasted with experiment for the case of the $Υ(5s)$ state. While globally the agreement is fair, we call the attention to some disagreement that could be a warning for the existence of more elaborate components in the state.

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arXiv2020

Signatures of the two $K_1(1270)$ poles in $D^+\to νe^+ V P$ decay

We analyze theoretically the $D^+\to νe^+ ρ\bar K$ and $D^+\to νe^+ \bar K^* π$ decays to see the feasibility to check the double pole nature of the axial-vector resonance $K_1(1270)$ predicted by the unitary extensions of chiral perturbation theory (UChPT). Indeed, within UChPT the $K_1(1270)$ is dynamically generated from the interaction of a vector and a pseudoscalar meson, and two poles are obtained for the quantum numbers of this resonance. The lower mass pole couples dominantly to $K^*π$ and the higher mass pole to $ρK$, therefore we can expect that different reactions weighing differently these channels in the production mechanisms enhance one or the other pole. We show that the different final $VP$ channels in $D^+\to νe^+ V P$ weigh differently both poles, and this is reflected in the shape of the final vector-pseudoscalar invariant mass distributions. Therefore, we conclude that these decays are suitable to distinguish experimentally the predicted double pole of the $K_1(1270)$ resonance.

hep-ph↗

arXiv2020

Theoretical interpretation of the $D^+_s \to π^+ π^0 η$ decay and the nature of $a_0(980)$

In a recent paper \cite{Ablikim:2019pit}, the BESIII collaboration reported the so-called first observation of pure $W$-annihilation decays $D^+_s \to a^+_0(980) π^0$ and $D_s^+ \to a^0_0(980)π^+$. The measured absolute branching fractions are, however, puzzlingly larger than those of other measured pure $W$-annihilation decays by at least one order of magnitude. In addition, the relative phase between the two decay modes is found to be about 180 degrees. In this letter, we show that all these can be easily understood if the $a_0(980)$ is a dynamically generated state from $\bar{K} K$ and $πη$ interactions in coupled channels. In such a scenario, the $D^+_s$ decay proceeds via internal $W$ emission instead of $W$-annihilation, which has a larger decay rate than $W$-annihilation. The proposed decay mechanism and the molecular nature of the $a_0(980)$ also provide a natural explanation to the measured negative interference between the two decay modes.

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arXiv2019

$χ_{c1}$ decays into a pseudoscalar meson and a vector-vector molecule

We evaluate ratios of the $χ_{c1}$ decay rates to $η$ ($η', K^-$) and one of the $f_0(1370)$, $f_0(1710)$, $f_2(1270)$, $f_2'(1525)$, $K^{*}_2(1430)$ resonances, which in the local hidden gauge approach are dynamically generated from the vector-vector interaction. With the simple assumption that the $χ_{c1}$ is a singlet of SU(3), and the input from the study of these resonances as vector-vector molecular states, we describe the experimental ratio $\mathcal{B}(χ_{c1} \rightarrow ηf_2(1270))/ \mathcal{B}(χ_{c1} \rightarrow η' f_2'(1525))$ and make predictions for six more ratios that can be tested in future experiments.

hep-ph↗

arXiv2019

Meson exchange between initial and final state and the $R_D$ ratio in the $\bar{B} \to D \barν \ell (\barν_ττ)$ reactions

We perform a calculation of the strong interaction effects between the $B$ and $D$ mesons in the $\bar{B} \to D \barν \ell$ reaction, as a crossing process of reactions with $BD$ in the final state, where the strong interaction between the mesons leads to a bound $BD$ state. We find corrections to the tree level amplitude of the order of $15-25\%$. We further see the effect of the corrections studied in the $R_D$ ratio for the rates of $\bar{B} \to D \barν_ττ$ and $\bar{B} \to D \barν_e \ell$ decays and find corrections of the order of $10\%$. Given the claims of $1.5\%$ precision in this ratio from fits to data within the standard model, any theoretical model aiming at describing this ratio within the same precision must take into account the corrections described in the present work.

hep-ph↗

arXiv2019

Triangle singularity in the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ decays

We study the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ reaction and find that the mechanism to produce this decay develops a triangle singularity around $M_{\rm inv}(K^- f_0/K^- a_0) \approx 1515$~MeV. The differential width $dΓ/ dM_{\rm inv}(K^- f_0/K^- a_0)$ shows a rapid growth around the invariant mass being 1515~MeV as a consequence of the triangle singularity of this mechanism, which is directly tied to the nature of the $f_0(980)$ and $a_0(980)$ as dynamically generated resonances from the interaction of pseudoscalar mesons. The branching ratios obtained for the $J/ψ\rightarrow K^+ K^- f_0(980)(a_0(980))$ decays are of the order of $10^{-5}$, accessible in present facilities, and we argue that their observation should provide relevant information concerning the nature of the low-lying scalar mesons.

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arXiv2019

Search for the $Σ^*$ state in $Λ^+_c \to π^+ π^0 π^-Σ^+$ decay by triangle singularity

A $Σ^*$ resonance with spin-parity $J^P = 1/2^-$ and mass in the vicinity of the $\bar{K}N$ threshold has been predicted in the unitary chiral approach and inferred from the analysis of CLAS data on the $γp \to K^+ π^0 Σ^0$ reaction. In this work, based on the dominant Cabibbo favored weak decay mechanism, we perform a study of $Λ_c^+ \to π^+ π^0 Σ^*$ with the possible $Σ^*$ state decaying into $π^- Σ^+$ through a triangle diagram. This process is initiated by $ Λ_c^+ \to π^+ \bar{K}^*N $, then the $\bar{K}^*$ decays into $\bar{K} π$ and $\bar{K} N$ produce the $Σ^*$ through a triangle loop containing $\bar{K}^* N \bar{K}$ which develops a triangle singularity. We show that the $π^- Σ^+$ state is generated from final state interaction of $\bar{K}N$ in $S$-wave and isospin $I=1$, and the $Λ_c^+ \to π^+ π^0 π^- Σ^+$ decay can be used to study the possible $Σ^*$ state around the $\bar{K}N$ threshold. The proposed decay mechanism can provide valuable information on the nature of the $Σ^*$ resonance and can in principle be tested by facilities such as LHCb, BelleII and BESIII.

hep-ph↗

arXiv2019

Further Theoretical Analysis on the $K^{-} {}^{3} \text{He} \to Λp n$ Reaction for the $\bar{K} N N$ Bound-State Search in the J-PARC E15 Experiment

Based on the scenario that a $\bar{K} N N$ bound state is generated and it eventually decays into $Λp$, we calculate the cross section of the $K^{-} {}^{3} \text{He} \to Λp n$ reaction, which was recently measured in the J-PARC E15 experiment. We find that the behavior of the calculated differential cross section $d ^{2} σ/ d M_{Λp} d q_{Λp}$, where $M_{Λp}$ and $q_{Λp}$ are the $Λp$ invariant mass and momentum transfer in the $(K^{-} , \, n)$ reaction in the laboratory frame, respectively, is consistent with the experiment. Furthermore, we can reproduce almost quantitatively the experimental data of the $Λp$ invariant mass spectrum in the momentum transfer window $350 \text{ MeV} /c < q_{Λp} < 650 \text{ MeV} /c$. These facts strongly suggest that the $\bar{K} N N$ bound state was indeed generated in the J-PARC E15 experiment.

nucl-th↗

arXiv2018

$\boldsymbolη$-$\boldsymbol{^4{\rm He}}$ interaction from the $\boldsymbol{d d \to η^4{\rm He}}$ reaction near threshold

We analyze the data on the total cross sections for the $dd \to η^4{\rm He}$ reaction close to threshold and look for possible $η^4 {\rm He}$ bound states. We develop a framework in which the $η^4{\rm He}$ optical potential is the key ingredient, rather than parameterizing the scattering matrix, as is usually done. The strength of this potential, together with some production parameters, are fitted to the available experimental data. The relationship of the scattering matrix to the optical potential is established using the Bethe-Salpeter equation and the $η^4{\rm He}$ loop function incorporates the range of the interaction given by the experimental $^4 {\rm He}$ density. However, when we look for poles of the scattering matrix, we get poles in the bound region, poles in the positive energy region or no poles at all. If we further restrict the results with constraints from a theoretical model with all its uncertainties the bound states are not allowed. However, we find a bump structure in $|T|^2$ of the $η^4{\rm He} \to η^4{\rm He}$ amplitude below threshold for the remaining solutions.

nucl-th↗

arXiv2018

The $X(4140)$ and $X(4160)$ resonances in the $e^+e^-\to γJ/ψϕ$ reaction

We investigate the $J/ψϕ$ invariant mass distribution of the $e^+e^-\to γJ/ψϕ$ reaction at a center of mass energy of $\sqrt{s}=4.6$~GeV measured by the BESIII collaboration, who concludes that no significant signals are observed for $e^+e^- \to γX(4140)$ because of the low statistics. We show, however, that the three bump structures in the $J/ψϕ$ invariant mass distribution, though given only by three data points, are compatible with the existence of the $X(4140)$ state, appearing as a peak, and a strong cusp structure at the $D^*_s\bar{D}^*_s$ threshold, resulting from the molecular nature of the $X(4160)$ state, which also provides a substantial contribution to the reaction. This is consistent with our previous analysis on the $B^+\to J/ψϕK^+$ decay measured by the LHCb collaboration. We strongly call for the measurement of this process with more statistics to further pin down the nature of the $X(4140)$ and $X(4160)$ resonances.

hep-ph↗

arXiv2018

Semileptonic decay of $B^{-}_c$ into $X(3930)$, $X(3940)$, $X(4160)$

We study the semileptonic decay of $B^{-}_c$ meson into $\barν l^-$ and the isospin zero $X(3930)~(2^{++})$, $X(3940)~(0^{++})$, $X(4160)~(2^{++})$ resonances. We look at the reaction from the perspective that these resonaces appear as dynamically generated from the vector-vector interaction in the charm sector, and couple strongly to $D^{*}\bar{D^{*}}$ and $D^{*}_{s}\bar{D_{s}^{*}}$. We also look into the $B^{-}_c \rightarrow \barν_{l} l^- D^{*}\bar{D^{*}}$ and $B^{-}_c \rightarrow \barν_{l} l^- D^{*}_{s}\bar{D_{s}^{*}}$ reactions close to threshold and relate the $D^{*}\bar{D^{*}}$ and $D^{*}_{s}\bar{D_{s}^{*}}$ mass distribution to the rate of production of the $X$ resonances.

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