arXiv subjects

Sergi Gonzàlez-Solís

Publications and source records attributed to Sergi Gonzàlez-Solís.

16 recordsLinked to original sources

arXiv2025

Global analysis of $μ\to e$ interactions in the SMEFT

We study current experimental bounds on charged lepton flavor violating (CLFV) $μ$-$e$ interactions in the model-independent framework of the Standard Model Effective Field Theory (SMEFT). Assuming a generic flavor structure in the quark sector, we consider the contributions of CLFV operators to low-energy observables, including $μ\to eγ$ and $μ\to e$ conversion for quark-flavor conserving operators and CLFV meson decays for quark-flavor violating operators. At high energy, we consider limits on CLFV decays of the Higgs and Z bosons and of the top quark, and obtain bounds on operators with light quarks by recasting searches for production of $eμ$ pairs in $pp$ collisions at the Large Hadron Collider (LHC). We connect observables at low- and high-energy by taking into account renormalization group running and matching between CLFV operators. We also discuss the sensitivity of the future Electron-Ion Collider, where the prospective bounds are derived by imposing simple cuts on final state particles. We find that, in a single operator scenario, bounds on purely leptonic operators are dominated by $μ\rightarrow e γ$ and $μ\rightarrow e$ conversion. Semileptonic operators with down-type quarks are also dominantly constrained by low-energy observables, while LHC searches lead the bounds on up-type quark-flavor violating operators. Taking simplified multiple-coupling scenarios, we show that it is easy to evade the strongest low-energy bounds from spin-independent $μ\rightarrow e$ conversion, and that collider searches are competitive and complementary to constraints from spin-dependent $μ\rightarrow e$ conversion and other low-energy probes.

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arXiv2025

Assessment of the $a_{2}(1320)$ tensor-meson contribution to $η/η^{\prime}\toπ^{0}γγ$ decays

In light of the recent measurement of the $η\toπ^{0}γγ$ decay by the KLOE-2 Collaboration, a previous analysis including vector- and scalar-meson exchange contributions using the VMD and L$σ$M frameworks, respectively, is extended in the present study to incorporate the effects of the $a_{2}(1320)$ tensor meson within a chiral context. Although the individual contribution of the $a_{2}$ is negligible, its destructive interference with the vector-meson resonances is found to be significant, representing approximately $18\%$ of the total signal and substantially affecting the diphoton invariant-mass distribution, especially at low $m_{γγ}^{2}$ values. The total decay rate is calculated to be $Γ(η\toπ^{0}γγ)=0.154(22)$ eV, which corresponds to a branching ratio of ${\rm BR}(η\toπ^{0}γγ)=1.17(17)\times10^{-4}$. This result is approximately $5σ$ below the reported value of the PDG, $2.55(22)\times10^{-4}$, while it is in very good agreement with the KLOE-2 measurement, $0.98(11_{\rm stat})(14_{\rm syst})\times10^{-4}$. In contrast, the total contribution of the $a_{2}$ is found to be negligible in $η^{\prime}\toπ^{0}γγ$, as this process is completely dominated by the exchange of an on-shell $ω$ vector resonance.

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arXiv2024

Improved $π^0,η,η^{\prime}$ transition form factors in resonance chiral theory and their $a_μ^{\rm{HLbL}}$ contribution

Working with Resonance Chiral Theory, within the two resonance multiplets saturation scheme, we satisfy leading (and some subleading) chiral and asymptotic QCD constraints and accurately fit simultaneously the $π^{0},η,η^{\prime}$ transition form factors, for single and double virtuality. In the latter case, we supplement the few available measurements with lattice data to ensure a faithful description. Mainly due to the new results for the doubly virtual case, we improve over existing descriptions for the $η$ and $η^\prime$. Our evaluation of the corresponding pole contributions to the hadronic light-by-light piece of the muon $g-2$ read: $a_μ^{π^{0}\text{-}\rm{pole}}=\left(61.9\pm0.6^{+2.4}_{-1.5}\right)\times10^{-11}$, $a_μ^{η\text{-}\rm{pole}}=\left(15.2\pm0.5^{+1.1}_{-0.8}\right)\times10^{-11}$ and $a_μ^{η^\prime\text{-}\rm{pole}}=\left(14.2\pm0.7^{+1.4}_{-0.9}\right)\times10^{-11}$, for a total of $a_μ^{π^0+η+η^{\prime}\text{-}\rm{pole}}=\left(91.3\pm1.0^{+3.0}_{-1.9}\right)\times10^{-11}$, where the first and second errors are the statistical and systematic uncertainties, respectively.

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arXiv2024

Final state rescattering effects in axio-hadronic $η$ and $η^{\prime}$ decays

It has been long-understood that final state rescattering effects provide $\mathcal{O}(1)$ corrections to hadronic meson decays rates, such as $η\toπππ$ and $η^{\prime}\toηππ$. Hence, one would expect that such effects would be just as important in axio-hadronic $η$ and $η^{\prime}$ decays, such as $η^{(\prime)}\toππa$, where $a$ is an axion or axion-like particle (ALP). And indeed they are, as we show in this paper by using the treatment of dispersion relations to include the effects of strong final state interactions in several axio-hadronic processes, namely, $η^{(\prime)}\toπ^0π^0 a$, $η^{(\prime)}\toπ^+π^- a$, and $η^{\prime}\toηπ^0 a$. We also compute the perturbative, leading order decay rates for multiple ALP emission, such as in $η^{(\prime)}\toπ^{0}aa$, $η^{\prime}\toηaa$ and $η^{(\prime)}\to aaa$, and briefly discuss the expected corrections from strong interactions and the processes that must be considered for an accurate rate estimation of these multi-ALP decay channels.

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arXiv2022

Sensitivity of the $η^{(\prime)}\toπ^{0}γγ$ and $η^{\prime}\toηγγ$ decays to a sub-GeV leptophobic $U(1)_{B}$ boson

The sensitivity of the rare decays $η^{(\prime)}\toπ^{0}γγ$ and $η^{\prime}\toηγγ$ to signatures of a leptophobic $B$ boson in the MeV-GeV mass range is analyzed in this work. By adding an explicit $B$-boson resonance exchange, $η\to Bγ\toπ^{0}γγ$, to the Standard Model contributions from vector and scalar meson exchanges, and employing experimental data for the associated branching ratios, it allows us to improve the current constraints on the $B$-boson mass $m_{B}$ and coupling to Standard Model particles $α_{B}$. From these constraints and the analysis of the available experimental $γγ$ invariant mass distribution, we show that a $B$-boson signature in the resonant mass range $m_{π^{0}}\lesssim m_{B}\lesssim m_η$ is strongly suppressed and would be very difficult to experimentally identify, assuming that the leptophobic $B$ boson only decays to Standard Model particles. In contrast, the limits outside this mass window are less stringent and the corresponding $t$- and $u$-channel signatures may still be observable in the data, as it occurs with the nonresonant Standard Model $ρ$, $ω$ and $ϕ$ meson exchanges. In addition, we make use of experimental data from the $η^{\prime}\toπ^{0}γγ$ and $η^{\prime}\toηγγ$ decays to explore larger $B$-boson masses. Our results are relevant for the $B$-boson search programs at existing and forthcoming light-meson facilities, such as KLOE(-II) and Jefferson Lab Eta Factory experiments.

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arXiv2021

Padé approximants to $B\toπ\ellν_{\ell}$ and $B_{s}\to K\ellν_{\ell}$ and determination of $|V_{ub}|$

In light of the first observation of the semileptonic decay $B^{0}_{s}\to K^{-}μ^{+}ν_μ$ by the LHCb collaboration, we revisit the determination of the CKM parameter $|V_{ub}|$ from exclusive semileptonic $B$-meson decays. A controlled theoretical input on the Standard Model $B\toπ$ and $B_{s}\to K$ vector and scalar form factors from Lattice QCD in the large $q^{2}$ region, in combination with experimental measurements of the differential $B\toπ\ellν_{\ell}$ and $B^{0}_{s}\to K^{-}μ^{+}ν_μ$ branching ratio distributions, has allowed us determine $|V_{ub}|=3.86(11)\times10^{-3}$ and $|V_{ub}|=3.58(9)\times10^{-3}$ from the analyses of the individual decay channels, respectively, and $|V_{ub}|=3.68(5)\times10^{-3}$ from a simultaneous analysis of both decays, which is only a $1.4\%$ error and differs by $1.8σ$ with respect to the value from inclusive determinations $|V_{ub}|=4.25(12)^{+15}_{-14}(23)\times10^{-3}$. Our results are based on the use of Padé approximants to the participating form factors, highlight the importance of the decay $B_{s}\to Kμν_μ$ in complementing the traditional $B\toπ\ellν_{\ell}$ one in the exclusive determination of $|V_{ub}|$, and allow obtain, to the best of our knowledge, the first correlated results for the $B\toπ$ and $B_{s}\to K$ vector and scalar form factors. We hope that our study strengthens the case for precise measurements of the differential $B_{s}\to K\ellν_{\ell}$ decay rate with a finer resolution of the $q^{2}$ bins, as it would definitely allow achieving more conclusive results for $|V_{ub}|$.

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arXiv2020

A theoretical analysis of the doubly radiative decays $η^{(\prime)}\toπ^0γγ$ and $η^\prime\toηγγ$

The scalar and vector meson exchange contributions to the doubly radiative decays $η^{(\prime)}\toπ^0γγ$ and $η^\prime\toηγγ$ are analysed within the Linear Sigma Model and Vector Meson Dominance frameworks, respectively. Predictions for the diphoton invariant mass spectra and the associated integrated branching ratios are given and compared with current available experimental data. Whilst a satisfactory description of the shape of the $η\toπ^{0}γγ$ and $η^\prime\toπ^{0}γγ$ decay spectra is obtained, thus supporting the validity of the approach, the corresponding branching ratios cannot be reproduced simultaneously. A first theoretical prediction for the recently measured $η^\prime\toηγγ$ by the BESIII collaboration is also presented.

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arXiv2019

Exclusive hadronic tau decays as probes of non-SM interactions

We perform a global analysis of exclusive hadronic tau decays into one and two mesons using the low-energy limit of the Standard Model Effective Field Theory up to dimension six, assuming left-handed neutrinos. A controlled theoretical input on the Standard Model hadronic form factors, based on chiral symmetry, dispersion relations, data and asymptotic QCD properties, has allowed us to set bounds on the New Physics effective couplings using the present experimental data. Our results highlight the importance of semileptonic $τ$ decays in complementing the traditional low-energy probes, such nuclear $β$ decays or semileptonic pion and kaon decays, and the high-energy measurements at LHC scales. This makes yet another reason for considering hadronic tau decays as golden modes at Belle-II.

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arXiv2019

Effective-field theory analysis of the $τ^{-}\to K^{-}(η^{(\prime)},K^{0}) ν_τ$ decays

We analyze the decays $τ^-\to K^-(η^{(\prime)},K^0) ν_τ$ within an effective field theory that includes the most general interactions between Standard Model fields up to dimension six, assuming left-handed neutrinos. In particular, we examine different interesting phenomenological observables i.e. decay spectra and branching ratio, Dalitz plot distributions and the forward-backward asymmetry, to explore the sensitivity of the corresponding decays to the effects of non-standard interactions. A controlled theoretical input on the Standard Model hadronic form factors, based on chiral symmetry, dispersion relations, data and asymptotic QCD properties, has allowed us to set bounds on the New Physics scalar and tensor effective couplings using the measured branching ratios. These are found to be in line with the findings of our series of previous analyses of two-meson tau decays and less precise than the constraints obtained from semileptonic kaon decays. In order to set stringent limits on these couplings, we will use all available experimental data of all possible di-meson tau decays. This is our next step plan, that we hope to be of interest for future experimental analyses of these decays.

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arXiv2019

Tau decays into two mesons: an overview

We review the state-of-the-art theoretical analyses of tau decays into a pair of mesons and a neutrino. The participant vector and scalar form factors, $f_{+}(s)$ and $f_{0}(s)$, are described in the frame of Chiral Perturbation Theory with resonances supplemented by dispersion relations, and the physical parameters of the intermediate resonances produced in the decay are extracted through the pole position of $f_{+,0}(s)$ in the complex plane. As a side result, we also determine the low-energy observables associated to the form factors. We hope our study to be of interest for present and future experimental analyses of these decays.

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arXiv2019

A dispersive analysis of the pion vector form factor and $τ^{-}\to K^{-}K_{S}ν_τ$ decay

We explore the potential of a combined analysis of the decays $τ^{-}\toπ^{-}π^{0}ν_τ$ and $τ^{-}\to K^{-}K_{S}ν_τ$ in the determination of the $ρ(1450)$ and $ρ(1700)$ resonance properties in the frame of resonance Chiral Theory supplemented by dispersion relations. On the one hand, we take advantage of the very precise data on the modulus squared of the pion vector form factor $|F_{V}^π|^{2}$ obtained by Belle to carry out a very dedicated analysis of the region where these resonances come up into play. Our study provides an improved treatment of the systematic theoretical errors and, as a most important result, we conclude that they dominate over the fit uncertainties in the determination of the $ρ(1450)$ and $ρ(1700)$ pole parameters and tend to be larger than in other determinations quoted in the literature where these errors were ignored or underestimated. The results of our analysis are summarized in numerical tables for the form factor modulus and phase, including both statistical and systematic errors, that can be found as ancillary material of this paper. As a byproduct, we also determine the low-energy observables of the pion vector form factor and the $ρ$-pole position. On the other hand, we benefit from the recent experimental data for the transition $τ^{-}\to K^{-}K_{S}ν_τ$ released by BaBar to perform a first analysis of its decay spectrum and discuss the role of these resonances in this decay. We point out that higher-quality data on the $K^{-}K_{S}$ decay channel will allow compete with the $|F_{V}^π|^{2}$ ones and improve the determination of the $ρ(1450)$ and $ρ(1700)$ resonance parameters as a result of a combined analysis. We hope our study to be of interest for present and future experimental analysis of these decays.

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arXiv2018

New spectrum of negative-parity doubly charmed baryons: Possibility of two quasistable states

The discovery of $Ξ_{cc}^{++}$ by the LHCb Collaboration triggers predictions of more doubly charmed baryons. By taking into account both the $P$-wave excitations between the two charm quarks and the scattering of light pseudoscalar mesons off the ground state doubly charmed baryons, a set of negative-parity spin-1/2 doubly charmed baryons are predicted already from a unitarized version of leading order chiral perturbation theory. Moreover, employing heavy antiquark-diquark symmetry the relevant low-energy constants in the next-to-leading order are connected with those describing light pseudoscalar mesons scattering off charmed mesons, which have been well determined from lattice calculations and experimental data. Our calculations result in a spectrum richer than that of heavy mesons. We find two very narrow $J^P=1/2^-$ $Ω_{cc}^P$, which very likely decay into $Ω_{cc}π^0$ breaking isospin symmetry. In the isospin-1/2 $Ξ_{cc}^P$ sector, three states are predicted to exist below 4.2~GeV with the lowest one being narrow and the other two rather broad. We suggest to search for the $Ξ_{cc}^{P}$ states in the $Ξ_{cc}^{++}π^-$ mode. Searching for them and their analogues are helpful to establish the hadron spectrum.

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arXiv2018

$η^{\prime}\toηππ$ decays in unitarized resonance chiral theory

We study the hadronic $η^{\prime}\toηππ$ decays within the framework of $U(3)_{L}\otimes U(3)_{R}$ Chiral Perturbation Theory including resonance states and the complete one-loop corrections. The amplitude is projected in partial waves and unitarized by means of the $N/D$ method resumming both the important $S$-and $D$-wave $ππ$ and the subleading $S$-wave $πη$ final-state interactions. The participating scalar multiplet mass and coupling strengths are determined from fits to the Dalitz plot experimental data recently released by the A2 collaboration. As a byproduct of our analysis, the associated Dalitz-plot slope parameters are found to be $a=-0.072(7)_{\rm{stat}}(8)_{\rm{syst}}\,, b=-0.052(1)_{\rm{stat}}(2)_{\rm{syst}}\,, d=-0.051(8)_{\rm{stat}}(6)_{\rm{syst}}$, which lie in the ballpark of the current experimental and theoretical determinations.

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arXiv2018

Study of $B\toπ\ellν_{\ell}$ and $B^{+}\toη^{(\prime)}\ell^{+}ν_{\ell}$ decays and determination of $|V_{ub}|$

We reassess the $B\toπ\ellν_{\ell}$ differential branching ratio distribution experimental data released by the BaBar and Belle Collaborations supplemented with all lattice calculations of the $B\toπ$ form factor shape available up to date obtained by the HPQCD, FNAL/MILC and RBC/UKQCD Collaborations. Our study is based on the method of Padé approximants, and includes a detailed scrutiny of each individual data set that allow us to obtain $|V_{ub}|=3.53(8)_{\rm{stat}}(6)_{\rm{syst}}\times10^{-3}$. The semileptonic $B^{+}\toη^{(\prime)}\ell^{+}ν_{\ell}$ decays are also addressed and the $η$-$η^{\prime}$ mixing discussed.

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arXiv2018

Insisting on the role of experimental data: the pseudoscalar-pole piece to the $(g_μ-2)$ and the $|V_{ub}|$ from $B \to π\ell ν_{\ell}$ differential branching ratio

We employ a mathematical framework based on rational approximants in order to calculate meson form factors. The method profits from unitary, is systematic and data based, and is able to ascribe a systematic uncertainty which provides for the desired model independence. Two examples are discussed: the transition form factor entering the pseudoscalar-pole piece of the hadronic light-by-light contribution to the anomalous magnetic moment of the muon, and the $B \to π$ form factor participating the $B\toπ\ellν_{\ell}$ differential branching ratios which allows to determine the $|V_{ub}|$ CKM parameter.

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arXiv2018

A data-driven approach to $π^{0}, η$ and $η^{\prime}$ single and double Dalitz decays

The dilepton invariant mass spectra and integrated branching ratios of the single and double Dalitz decays $\mathcal{P}\to\ell^{+}\ell^{-}γ$ and $\mathcal{P}\to\ell^{+}\ell^{-}\ell^{+}\ell^{-}$ ($\mathcal{P}=π^{0}, η, η^{\prime}$; $\ell=e$ or $μ$) are predicted by means of a data-driven approach based on the use of rational approximants applied to $π^{0}, η$ and $η^{\prime}$ transition form factor experimental data in the space-like region.

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