arXiv subjects

Genaro Toledo

Publications and source records attributed to Genaro Toledo.

17 recordsLinked to original sources

arXiv2026

Effect of $K^*$ meson magnetic dipole moment on the $e^+e^- \to K^+ K^-\pi^0 \pi^0 $ cross section

We explore the sensitivity of the $e^{+} e^{-} \to K^+ K^- 2 \pi^0$ cross section to the magnetic dipole moment (MDM) of the $K^*$ vector meson. We describe the $\gamma^* \to 2K2\pi$ vertex using a vector meson dominance model, including the intermediate resonant contributions relevant for energies below 2.4 GeV. Using BaBar data for this process, we show that this observable is indeed sensitive to the MDM of the $K^*$; we obtain a central value for the MDM of $\mu_{K^*}=4.5$ and an upper bound of $\bar{\mu}_{K^*} = 6.3$, in units of $e/2 m_{K^*}$. We emphasize the need for higher precision data to provide a first data-driven determination of this parameter to confront it with theoretical predictions.

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arXiv2025

Beyond scalar QED radiative corrections: the $\rho^{\pm}-\rho^0$ width difference, FSR corrections and their impact on $\Delta a_{\mu}^{\rm HVP, LO}[\tau]$

In a previous paper arXiv:0708.3256 [hep-ph] we have calculated the radiative corrections to $\rho \to \pi\pi$ decays, aiming to estimate the width difference between charged and neutral rho mesons. There, we have used the scalar QED approximation and taken the convection terms to keep the loop contributions finite in the case of charged rho meson decays. Here we compute the radiative corrections by considering the electromagnetic structure of charged mesons and we also include the full Lorentz structure of the electromagnetic vertices. We re-evaluate the width difference of $\rho^{\pm}-\rho^0$ vector mesons and calculate the structure-dependent contributions to Final State Radiation terms in the $e^+e^-\to \pi^+\pi^-$ cross section. Both effects are important inputs for evaluating the isospin breaking corrections in the dominant hadronic vacuum polarization contributions to the muon $g-2$ when using $\tau$ lepton data.

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arXiv2025

Lepton number violating and conserving heavy baryon four-body decays in the presence of two almost degenerate heavy neutrinos

We study the four-body heavy baryon decay, including two leptons in the final state, of the form $B_A \to B_B P \ell_\alpha \ell_\beta$, which can be either a lepton number conserving (LNC) or a lepton number violating (LNV) process (where $B$, $P$ and $\ell$ are baryons, pseudoscalar mesons and leptons, respectively), including all kinematic allowed lepton pair possibilities. We work beyond the simplified assumption of a single heavy Majorana neutrino mixing with the active sector, considering potential interference effects when including two nearly degenerate heavy Majorana neutrinos. Particularly, we provide a first estimate of the decay channels involving different flavors for the external leptons (e.g., muon-tau), and elaborate on the interference pattern due to leptons exchange. We show that the results for the two heavy almost degenerate neutrinos can be recast into a single Majorana neutrino, and exhibit the features for both the LNC and LNV scenarios. We determine the potential exclusion region for the mass and heavy-light mixing parameters, of the neutrinos driving the decay, including finite size detector effects, and compare them with those from direct searches and $\tau$ and meson decays. We also obtain the Branching ratio as a function of the heavy neutrino mass for the current upper limit of the heavy-light mixings.

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arXiv2024

The $\rho$ meson magnetic dipole moment from BaBar $e^+e^- \to \pi^+ \pi^-\pi^0 \pi^0 $ cross section measurement

We obtain the value of the magnetic dipole moment of the $\rho$ meson, using data from the BaBar Collaboration for the $e^{+} e^{-} \to \pi^+ \pi^- 2 \pi^0$ process. The considered center of mass energy range is from 0.9 to 1.8 GeV. We describe the $\gamma^* \to 4\pi$ vertex using a vector meson dominance model, including the intermediate resonant contributions relevant at these energies. We find $\mu_\rho = 2.7 \pm 0.3 $ in $e/2 m_\rho$ units. We improve on the previous extracted value, where preliminary data from the same collaboration was used, by considering definite data, better grounded values of the parameters involved and explicit gauge invariant description of the process.

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arXiv2024

Exploring hadronic de-excitation via Lepton Flavor Violation

In this work, we consider a hadronic de-excitation mechanism via lepton flavor violation (LFV). Namely, for vector and pseudoscalar meson decays of the form $V^\prime \to V \mu e$ and $P^\prime \to P \mu e$, respectively. They are described considering effective dim-5 and dim-7 operators. Using the current bounds for the effective couplings obtained from direct processes, we exhibit the different features in the dilepton invariant mass distribution and the branching ratios, depending on the effective operator. We consider hadronic states, from light mesons to quarkonia. We show that the branching ratios of quarkonia system for LFV are comparable with the estimates in other hadronic systems. Our results show that the dilepton invariant mass may be useful to constrain individual contributions and help disentangle them, when complemented with observables from nuclei.

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arXiv2024

Sizing the double pole resonant enhancement in $e^{+}e^{-} \to π^{0} π^{0} γ$ cross section and $τ^{-} \to π^{-}π^{0} ν_τγ$ decay

The enhancement mechanism due to the resonant properties of the $ρ$ and $ω$ mesons, which are close in mass, are analysed when such resonances carry different momenta. Considerations from the particular process where they appear to the individual resonant features are at play for the appearance of the global resonant manifestation. In this work, we first consider the $e^+e^- \to π^0 π^0 γ$ process. We use the differential cross section at a given angle of emission of one of the pions, to tune the individual features of the two resonances and exhibit how both resonances combine to produce the enhancement. Then, we incorporate the $ρ^\prime$ using the information obtained from the $ e^+e^- \to π^0 π^0 γ$ total scattering process and show that, it becomes important thanks to the same enhancement mechanism between the $ρ$ and the $ω$. In a second step, we use a similar approach to describe a model dependent contribution to the $τ^- \to π^-π^0ν_τγ$ decay, the so-called $ω$ channel. We show that the dipion invariant mass distribution at particular angles is sensitive to the individual resonant states. We compute the interference of this channel with the known dominant model independent contribution, and show how a better knowledge of the $e^+e^- \to π^0 π^0 γ$ process can help to properly account for such model dependent effects. The implication on the isospin symmetry breaking correction to tau-based estimates of the muon magnetic dipole moment is assessed.

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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

Role of the $ρ(1450)$ in low-energy observables from an analysis in the meson dominance approach

The $ρ(1450)$ vector meson ($ρ^\prime$) is becoming increasingly important to properly describe precision observables. We analyse a set of decay modes and cross sections, in the low-energy regime, to determine the role played by this meson. This is done through the extraction of the parameters for its description, in the context of the vector meson dominance model and its effective hadronic interactions, involving the low mass lying hadrons ($ρ$, $ω$ and $π$). In a first step, we determine the parameters of the model from ten decay modes which are insensitive to the $ρ^\prime$. Then, we consider the $ω\rightarrow 3π$ decay and exhibit the need to extend the description, by incorporating the $ρ^\prime$ and a contact term as prescribed by the Wess-Zumino-Witten anomaly. In a second step, we incorporate the data from the $e^+e^- \rightarrow 3π$ cross section (as measured by SND, CMD2, BABAR and BESIII) and then the $e^+e^- \rightarrow π^0 π^0 γ$ data (as measured by SND and CDM2) to further restrict the $ρ^\prime$ parameters validity region. As an application of the results, we compute the $e^+e^- \rightarrow 4π$ cross section for the so-called omega channel, measured by BABAR, and find a good description of the data considering the parameters found. As a byproduct, the coupling between $ρ$, $ω$ and $π$ ($g_{ρωπ}= 11.314 \pm 0.383$ GeV$^{-1}$) is found to be consistent with all the relevant observables, upon the inclusion of the $ρ^\prime$ and the contact term.

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arXiv2022

Resonant Majorana neutrino effects in $Δ$L=2 four-body hyperon decays

We computed the $Σ^{-}\to nπ^+e^-\ell^-$ ($\ell=e,μ$), $Ξ^-\to Λπ^+e^-e^-$, and $Λ\to pπ^+e^-e^-$ lepton number violating (LNV) hyperon decays mediated by a resonant Majorana neutrino. The expected hyperon production rate of experiments like BES-III of around $10^6-10^8$ may allow searching for these rare hyperon decays at enough sensitivities. We illustrate the limits on the new heavy mixing parameters derived from these hyperon channels and compare them with other LNV meson decays in similar mass regions of the resonant neutrino state.

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arXiv2022

Taming the long distance effects in the $D^{+}_{s}\rightarrow π^{+}\ell^{-}\ell^{+}$ decay

The semileptonic decay $D^{+}_{s}\rightarrow π^{+}\ell^{-}\ell^{+}$, where $\ell=e, \ μ$, is used as a reference channel when looking for suppressed or forbidden processes of the standard model of the form $D_{s}\rightarrow P\ell^{\pm}\ell^{\prime+}$. The process is dominated by hadronic resonances from the $η$ to the $ϕ$ meson region, usually excluded due to the large uncertainties associated. In this work, we explore the role of the parameters involved in the resonance region. We focus in the relative strong phase between the $ρ$ and the $ϕ$ meson ($δ_{ρϕ}$). We argue that this parameter can be bound from LHCb data of the di-muon invariant mass in the $D^{+}_{s}\rightarrow π^{+}μ^{-}μ^{+}$ decay and we perform a fit to provide a first approach to it. We obtain $δ_{ρϕ}=(0.44 \pm 0.24) π$. In contradistinction, it would be useful to consider observables insensitive to this phase. We first compute the invariant mass of the lepton pair at a given angle of one of the leptons emission with respect to the pion, and then we compute the forward-backward distribution at such angle. We show that for the latter observable the resonance region is smeared, exhibiting no dependence on the $δ_{ρϕ}$ phase, although global effects are observed by comparing with the pure phase space approach. In order to consider this observable in more general scenarios, we analyse the behavior for the resonant background process $D^{+}_{s}\rightarrow πππ$, the short distance contribution in the standard model, and the charged Higgs mediated process as given by the two Higgs doublet model, which exhibit distinguishable features among themselves.

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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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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

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.

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arXiv2019

$R_{D^*}$ or $R_{Dπ}$: closing the theoretical gap?

Measurements of the $R_{D^*}$ parameter remain in tension with the standard model prediction, despite recent results helping to close the gap. In this work, we revisit the standard model considerations for the prediction. We pay particular attention to the theoretical prediction considering the full 4-body decay $(B\rightarrow lνD^* \to lνDπ)$, which introduces the longitudinal degree of freedom of the $D^*$. We show that this does not introduce sizeable effects at the current precision. This modifies our previous finding (Phys. Rev. D 98 056014 (2018)) where a numerical bug led us to a different conclusion. Thus, the results on $R_{Dπ}$ are consistent with $R_{D^*}$, and the difference between the several values can be traced back to the form factor used and the restrictions incorporated to determine their parameters. There is still tension between the experimental world average and the most accurate theoretical estimate, leaving the possibility of presence of new physics scenarios open.

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arXiv2019

Closing the Gap on $R_{D^*}$ by including longitudinal effects

Measurements of the $R_{D^*}\equiv\mathrm{Br}(B\rightarrow τνD^*)/\mathrm{Br}(B\rightarrow eνD^*)$ parameter remain in tension with the standard model prediction, despite recent results helping to close the gap. The standard model prediction it is compared with considers the $D^*$ as an external particle, even though what is detected in experiments is a $Dπ$ pair it decays into, from which it is reconstructed. We argue that the experimental result must be compared with the theoretical prediction considering the full 4-body decay $(B\rightarrow lνD^* \to lνDπ)$. We show that the longitudinal degree of freedom of the off-shell $D^*$ helps to further close the disagreement gap with experimental data. We find values for the ratio $R_{Dπ}^l \equiv {\mathrm{Br}(B\rightarrow τν_τD π)}/\mathrm{Br}(B\rightarrow lν_l Dπ)$ of $R_{Dπ}^e=0.274\pm0.003$ and $R_{Dπ}^μ=0.275\pm0.003$, where the uncertainty comes from the uncertainty of the form factors parameters. Comparing against $R_{Dπ}$ reduces the gap with the latest LHCb result from $1.1σ$ to $0.48σ$, while the gap with the latest Belle result is reduced from $0.42σ$ to just $0.10σ$ and with the world average results from $3.7σ$ to $2.1σ$. Erratum added at the end of the file.

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arXiv2019

Effective-field theory analysis of the $τ^{-}\rightarrow (K π)^{-}ν_τ$ decays

We analyze the $τ^-\to(Kπ)^-ν_τ$ decays within an effective field theory description of heavy new physics (NP) modifying the SM left-handed weak charged current and include refined SM input for the participant meson form factors exploiting chiral symmetry, dispersion relations and (lattice) data. We include the leading dimension six operators and work at linear order in the effective couplings. Within this setting we: i) follow the derivation in Phys. Rev. Lett. 120 (2018) no.14, 141803 where it was proved unambiguously that it is impossible to understand the BaBar anomaly in the CP asymmetry measurement within this framework. We allow for reasonable variations of the hadronic input involved and study the associated uncertainty; ii) first show that the anomalous bump present in the published Belle data for the $K_Sπ^-$ invariant mass distribution close to threshold cannot be due to heavy NP; iii) first bind the heavy NP effective couplings using $τ^-\to(Kπ)^-ν_τ$ decays and show that they are competitive with those found in hyperon semileptonic decays (but clearly not with those obtained in Kaon (semi)leptonic decays for NP scalar currents). We put forward that the comparison of the considered tau decays with (semi)leptonic kaon and hyperon decays provide with meaningful tests of lepton universality for (NP) tensor interactions. We also compare the SM predictions with the possible deviations caused by NP in a couple of Dalitz plot distributions, in the forward-backward asymmetry and in the di-meson invariant mass distribution and discuss the most interesting measurements to be performed at Belle-II using these decays data.

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