arXiv subjects

E. Oset

Publications and source records attributed to E. Oset.

At least 91 records · Page 5Linked to original sources

arXiv2018

Description of the $Ξ_c$ and $Ξ_b$ states as molecular states

In this work we study several $Ξ_c$ and $Ξ_b$ states dynamically generated from the meson-baryon interaction in coupled channels, using an extension of the local hidden gauge approach in the Bethe-Salpeter equation. These molecular states appear as poles of the scattering amplitudes, and several of them can be identified with the experimentally observed $Ξ_c$ states, including the $Ξ_c(2790)$, $Ξ_c(2930)$, $Ξ_c(2970)$, $Ξ_c(3055)$ and $Ξ_c(3080)$. Also, for the recently reported $Ξ_b(6227)$ state, we find two poles with masses and widths remarkably close to the experimental data, for both the $J^P=1/2^-$ and $J^P=3/2^-$ sectors.

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arXiv2018

$τ$ decay into a pseudoscalar and an axial-vector meson

We study theoretically the decay $τ^- \to ν_τP^- A$, with $P^-$ a $π^-$ or $K^-$ and $A$ an axial-vector resonance $b_1(1235)$, $h_1(1170)$, $h_1(1380)$, $a_1(1260)$, $f_1(1285)$ or any of the two poles of the $K_1(1270)$. The process proceeds through a triangle mechanism where a vector meson pair is first produced from the weak current and then one of the vectors produces two pseudoscalars, one of which reinteracts with the other vector to produce the axial resonance. For the initial weak hadronic production we use a recent formalism to account for the hadronization after the initial quark-antiquark pair produced from the weak current, which explicitly filters G-parity states and obtain easy analytic formulas after working out the angular momentum algebra. The model also takes advantage of the chiral unitary theories to evaluate the vector-pseudoscalar amplitudes, where the axial-vector resonances were obtained as dynamically generated from the VP interaction. We make predictions for invariant mass distribution and branching ratios for the channels considered.

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arXiv2018

Polarization amplitudes in $τ^- \to ν_τ V P$ decay beyond the standard model

We use a recent formalism of the weak hadronic reactions $τ^- \to ν_τ M_1 M_2$ to study the helicity amplitudes in $τ^- \to ν_τ V P$ decay. This recent formalism maps the transition matrix elements at the quark level into hadronic matrix elements, and finally writes the weak matrix elements in terms of easy analytical formulas evaluated by means of an elaborate angular momentum algebra. The formalism provides directly the amplitudes for the different spin third components of the vector mesons involved. We extend the formalism to a general case, with the operator $γ^μ-αγ^μγ_5$, that can account for different models beyond the standard model and study in detail the $τ^- \to ν_τ K^{*0} K^{-} $ reaction for the different helicities of the $K^{*0}$. The results are shown in terms of the $α$ parameter that differs for each model. We find that $\frac{d Γ}{d M_{\rm inv}^{(K^{*0} K^{-} )}}$ is very different for the different components $M=\pm 1, 0$ and in particular the magnitude $\frac{d Γ}{d M_{\rm inv}^{(K^{*0} K^{-} )}}|_{M=+1} -\frac{d Γ}{d M_{\rm inv}^{(K^{*0} K^{-} )}}|_{M=-1} $ is very sensitive to the $α$ parameter, which makes the investigation of this magnitude a most welcome initiative to test different models beyond the standard model.

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arXiv2018

Helicity amplitudes in $B \to D^{*} \barν l$ decay

We use a recent formalism of the weak hadronic reactions that maps the transition matrix elements at the quark level into hadronic matrix elements, evaluated with an elaborate angular momentum algebra that allows finally to write the weak matrix elements in terms of easy analytical formulas. In particular they appear explicitly for the different spin third components of the vector mesons involved. We extend the formalism to a general case, with the operator $γ^μ-αγ^μγ_5$, that can accommodate different models beyond the standard model and study in detail the $B \to D^{*} \barν l$ reaction for the different helicities of the $D^*$. The results are shown for each amplitude in terms of the $α$ parameter that is different for each model. We show that $\frac{d Γ}{d M_{\rm inv}^{(νl)}}$ is very different for the different components $M=\pm 1, 0$ and in particular the magnitude $\frac{d Γ}{d M_{\rm inv}^{(νl)}}|_{M=-1} -\frac{d Γ}{d M_{\rm inv}^{(νl)}}|_{M=+1} $ is very sensitive to the $α$ parameter, which suggest to use this magnitude to test different models beyond the standard model. We also compare our results with the standard model and find very similar results, and practically identical at the end point of $M_{\rm inv}^{(νl)}= m_B- m_{D^*}$.

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arXiv2018

Triangle singularity in $τ^- \to ν_τπ^- f_0(980)$ ($a_0(980)$) decays

We study the triangle mechanism for the decay $τ^- \to ν_τπ^- f_0(980)$, with the $f_0(980)$ decaying into $π^+ π^- $. This process is initiated by $τ^- \to ν_τK^{*0} K^-$ followed by the $K^{*0}$ decay into $π^- K^+$, then the $K^- K^+$ produce the $f_0(980)$ through a triangle loop containing $ K^* K^+ K^-$ which develops a singularity around $1420$~MeV in the $πf_0(980)$ invariant mass. We find a narrow peak in the $π^+ π^-$ invariant mass distribution, which originates from the $f_0(980)$ amplitude. Similarly, we also study the triangle mechanism for the decay $τ\to νπ^- a_0(980)$, with the $a_0(980)$ decaying into $π^0 η$. The final branching ratios for $π^- f_0(980)$ and $π^- a_0(980)$ are of the order of $4 \times 10^{-4}$ and $7 \times 10^{-5}$, respectively, which are within present measurable range. Experimental verification of these predictions will shed light on the nature of the scalar mesons and on the origin for the "$a_1(1420)$" peak observed in other reactions.

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arXiv2018

Considerations on the Schmid theorem for triangle singularities

We investigate the Schmid theorem, which states that if one has a tree level mechanism with a particle decaying to two particles and one of them decaying posteriorly to two other particles, the possible triangle singularity developed by the mechanism of elastic rescattering of two of the three decay particles does not change the cross section provided by the tree level. We investigate the process in terms of the width of the unstable particle produced in the first decay and determine the limits of validity and violation of the theorem. One of the conclusions is that the theorem holds in the strict limit of zero width of that resonance, in which case the strength of the triangle diagram becomes negligible compared to the tree level. Another conclusion, on the practical side, is that for realistic values of the width, the triangle singularity can provide a strength comparable or even bigger than the tree level, which indicates that invoking the Schmid theorem to neglect the triangle diagram stemming from elastic rescattering of the tree level should not be done. Even then, we observe that the realistic case keeps some memory of the Schmid theorem, which is visible in a peculiar interference pattern with the tree level.

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arXiv2018

The $B^+ \to J/ψωK^+ $ reaction and $D^\bar{D}^$ molecular states

We study the $B^+ \to J/ψωK^+ $ reaction, measured by the LHCb collaboration, and show that it is driven by the presence of two resonances, the $X(3940)$ and $X(3930)$, that are of molecular nature and couple most strongly to $D^* \bar{D}^*$, but also to $J/ψω$. Because of that, in the $J/ψω$ mass distribution we find a peak related to the excitation of the resonances and a cusp with large strength at the $D^* \bar{D}^*$ threshold.

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arXiv2018

Coupled channels dynamics in the generation of the $Ω(2012)$ resonance

We look into the newly observed $Ω(2012)$ state from the molecular perspective in which the resonance is generated from the $\bar{K} Ξ^*$, $ηΩ$ and $\bar{K} Ξ$ channels. We find that this picture provides a natural explanation of the properties of the $Ω(2012)$ state. We stress that the molecular nature of the resonance is revealed with a large coupling of the $Ω(2012)$ to the $\bar{K} Ξ^*$ channel, that can be observed in the $Ω(2012) \rightarrow \bar{K} πΞ$ decay which is incorporated automatically in our chiral unitary approach via the use of the spectral function of $Ξ^*$ in the evaluation of the $\bar{K} Ξ^*$ loop function.

hep-ph↗

arXiv2018

Semileptonic decays of $B^{()}$, $D^{()}$ into $ν l$ and pseudoscalar or vector mesons

We perform a study of the $B^{(*)}$, $D^{(*)}$ semileptonic decays, using a different method than in conventional approaches, where the matrix elements of the weak operators are evaluated and a detailed spin-angular momentum algebra is performed to obtain very simple expressions at the end for the different decay modes. Using only one experimental decay rate in the $B$ or $D$ sectors, the rates for the rest of decay modes are predicted and they are in good agreement with experiment. Some discrepancies are observed in the $τ$ decay mode for which we find an explanation. We perform evaluations for $B^*$ and $D^*$ decay rates that can be used in future measurements, now possible in the LHCb collaboration.

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arXiv2018

Pseudoscalar or vector meson production in non-leptonic decays of heavy hadrons

We have addressed the study of non-leptonic weak decays of heavy hadrons ($Λ_b, Λ_c, B$ and $D$), with external and internal emission to give two final hadrons, taking into account the spin-angular momentum structure of the mesons and baryons produced. A detailed angular momentum formulation is developed which leads to easy final formulas. By means of them we have made predictions for a large amount of reactions, up to a global factor, common to many of them, that we take from some particular data. Comparing the theoretical predictions with the experimental data, the agreement found is quite good in general and the discrepancies should give valuable information on intrinsic form factors, independent of the spin structure studied here. The formulas obtained are also useful in order to evaluate meson-meson or meson-baryon loops, for instance of $B$ decays, in which one has PP, PV, VP or VV intermediate states, with P for pseudoscalar mesons and V for vector meson and lay the grounds for studies of decays into three final particles.

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arXiv2018

Dynamical Hadrons

In this talk I briefly review the theory of resonances dynamically generated from hadron-hadron scattering, sometimes referred to as "molecules"S. I give some classical examples of meson-meson and meson-baryon systems, as well as a few examples of different approaches to describe the interaction between hadrons. To conclude, I comment on a few recent works that suggest that some of the five new narrow $Ω_c$ states, recently discovered by the LHCb collaboration, can be interpreted as meson-baryon molecules.

hep-ph↗

arXiv2018

$τ^- \to ν_τ M_1 M_2$, with $M_1, M_2$ pseudoscalar or vector mesons

We perform a calculation of the $τ^- \to ν_τ M_1 M_2$, with $M_1, M_2$ either pseudoscalar or vector mesons using the basic weak interaction and angular momentum algebra to relate the different processes. The formalism also leads to a different interpretation of the role played by $G$-parity in these decays. We also observe that, while $p$-wave $M_1 M_2$ production is compatible with chiral perturbation theory and experiment, $VP$ and $VV$ $p$-wave production is clearly incompatible with experiment and we develop the formalism also in this case. We compare our results with experiment and make predictions for unmeasured decays, and we show the value of these reactions, particularly if the $M_1 M_2$ mass distribution is measured, as a tool to learn about the meson-meson interaction and the nature of some resonances, coupling to two mesons, which are produced in such decays.

hep-ph↗

arXiv2018

Effective Field Theories in a Finite Volume

In this talk I present the formalism we have used to analyze Lattice data on two meson systems by means of effective field theories. In particular I present the results obtained from a reanalysis of the lattice data on the $KD^{(*)}$ systems, where the states $D^*_{s0}(2317)$ and $D^*_{s1}(2460)$ are found as bound states of $KD$ and $KD^*$, respectively. We confirm the presence of such states in the lattice data and determine the contribution of the $KD$ channel in the wave function of $D^*_{s0}(2317)$ and that of $KD^*$ in the wave function of $D^*_{s1}(2460)$. Our findings indicate a large meson-meson component in the two cases.

hep-lat↗

arXiv2018

Doubly charmed $Ξ_{cc}$ molecular states from meson-baryon interaction

Stimulated by the new experimental LHCb findings associated with the $Ω_c$ states, some of which we have described in a previous work as being dynamically generated through meson-baryon interaction, we have extended this approach to make predictions for new $Ξ_{cc}$ molecular states in the $C=2$, $S=0$ and $I=1/2$ sector. These states manifest themselves as poles in the solution of the Bethe-Salpeter equation in coupled channels. The kernels of this equation were obtained using the Lagrangians coming from the hidden local gauge symmetry, where the interactions are dominated by the exchange of light vector mesons. The extension of this approach to the heavy sector stems from the realization that the dominant interaction corresponds to having the heavy quarks as spectators, which implies the preservation of the heavy quark symmetry. As a result, we get several states: two states from the pseudoscalar meson-baryon interaction with $J^P=1/2^-$, and masses around $4080$ and $4090$ MeV, and one at $4150$ MeV for $J^P=3/2^-$. Furthermore, from the vector meson-baryon interaction we get three states degenerate with $J^P=1/2^-$ and $3/2^-$ from $4220$ MeV to $4330$ MeV, and two more states around $4280$ MeV and $4410$ MeV, degenerate with $J^P=1/2^-,\, 3/2^-$ and $5/2^-$.

hep-ph↗

arXiv2018

Anomalous enhancement of the isospin-violating $Λ(1405)$ production by a triangle singularity in $Λ_c\rightarrowπ^+π^0π^0Σ^0$

The decay of $Λ_c^+$ into $π^+π^0Λ(1405)$ with the $Λ(1405)$ decay into $π^0Σ^0$ through a triangle diagram is studied. 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 $Λ(1405)$ through a triangle loop containing $\bar{K}^*N\bar{K}$ which develops a singularity around $1890$ MeV. This process is prohibited by the isospin symmetry, but the decay into this channel is enhanced by the contribution of the triangle diagram, which is sensitive to the mass of the internal particles. We find a narrow peak in the $π^0Σ^0$ invariant mass distribution, which originates from the $Λ(1405)$ amplitude, but is tied to the mass differences between the charged and neutral $\bar{K}$ or $N$ states. The observation of the unavoidable peak of the triangle singularity in the isospin-violating $Λ(1405)$ production would provide further support for hadronic molecular picture of the $Λ(1405)$ and further information on the $\bar{K} N $ interaction.

hep-ph↗

arXiv2018

Molecular $Ω_b$ states

Motivated by the recent finding of five $Ω_c$ states by the LHCb collaboration, and the successful reproduction of three of them in a recent approach searching for molecular states of meson-baryon with the quantum numbers of $Ω_c$, we extend these ideas and make predictions for the interaction of meson-baryon in the beauty sector, searching for poles in the scattering matrix that correspond to physical states. We find several $Ω_b$ states: two states with masses 6405~MeV and 6465~MeV for $J^P= \frac{1}{2}^-$; two more states with masses 6427~MeV and 6665~MeV for $\frac{3}{2}^-$; and three states between 6500 and 6820~MeV, degenerate with $J^P=\frac{1}{2}^-,\,\frac{3}{2}^-$, stemming from the interaction of vector-baryon in the beauty sector.

hep-ph↗

arXiv2018

Triangle singularity in $τ\to f_1(1285)πν_τ$ decay

We show that the $τ^-$ decay into $f_1(1285)π^-ν_τ$ is dominated by a triangle loop mechanism with $K^*$, $\bar K^*$ and $K$ (or $\bar K$) as internal lines, which manifests a strong enhancement reminiscent of a nearby singularity present in the narrow $K^*$ limit. The $f_1(1285)$ is then produced by its coupling to the $K^*\bar K$ and $\bar K^*K$ which is obtained from a previous model where this resonance was dynamically generated as a molecular $K^*\bar K$ (or $\bar K^*K$) state using the techniques of the chiral unitary approach. We make predictions for the $f_1 π$ mass distribution which significantly deviates from the phase-space shape, due to the distortion caused by the triangle singularity. We find a good agreement with the experimental value within uncertainties for the integrated partial decay width, which is a clear indication of the importance of the triangle singularity in this decay and supports the dynamical origin of the $f_1(1285)$ as a $K^*\bar K$ and $\bar K^* K$ molecular state.

hep-ph↗

arXiv2018

$\boldsymbol{Ω_b^- \to (Ξ_c^+ \, K^-) \, π^-}$ and the $\boldsymbol{Ω_c}$ states

We study the weak decay $Ω_b^- \to (Ξ_c^+ \, K^-) \, π^-$, in view of the narrow $Ω_c$ states recently measured by the LHCb collaboration and later confirmed by the Belle collaboration. The $Ω_c(3050)$ and $Ω_c(3090)$ are described as meson-baryon molecular states, using an extension of the local hidden gauge approach in coupled channels. We investigate the $ΞD$, $Ξ_c \bar K$ and $Ξ_c^\prime \bar K$ invariant mass distributions making predictions that could be confronted with future experiments, providing useful information that could help determine the quantum numbers and nature of these states.

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