arXiv subjects

Néstor Quintero

Publications and source records attributed to Néstor Quintero.

5 recordsLinked to original sources

arXiv2023

$B$ meson anomalies within the triplet vector boson model to the light of recent measurements from LHCb

The triplet vector boson (TVB) is a simplified new physics model involving massive vector bosons transforming as a weak triplet vector. Such a model has been proposed as a combined explanation of the anomalous $b \to sμ^+μ^-$ and $b \to c τ\barν_τ$ data (the so-called $B$ meson anomalies). In this work, we carry out an updated view of the TVB model by incorporating the most recent 2022 and 2023 LHCb measurements on the lepton flavor universality ratios $R(D^{(\ast)}) = {\rm BR}(B \to D^{(\ast)}τ\barν_τ)/{\rm BR}(B \to D^{(\ast)}\ell^\prime \barν_{\ell^\prime})$, $R(Λ_c) = {\rm BR}(Λ_b \to Λ_cτ\barν_τ)/{\rm BR}(Λ_b \to Λ_cμ\barν_μ)$, and $R_{K^{(\ast)}} = {\rm BR}(B \to K^{(\ast)}μ^+μ^-)/{\rm BR}(B \to K^{(\ast)}e^+e^-)$. We perform a global fit to explore the allowed parameter space by the new data and all relevant low-energy flavor observables. Our results are confronted with the recent high-mass dilepton searches at the Large Hadron Collider (LHC). We find that for a heavy TVB mass of 1 TeV a common explanation of the $B$ meson anomalies is possible for all data with the recent LHCb measurements on $R(D^{(\ast)})$, in consistency with LHC constraints. However, this framework is in strong tension with LHC bounds when one considers all data along with the world average values (BABAR, Belle, and LHCb) on $R(D^{(\ast)})$. Future measurements will be required in order to clarify such a situation. In the end, the implications of our phenomenological analysis of the TVB model to some known flavor parametrizations are also discussed.

hep-ph↗

arXiv2022

Singlet vector leptoquark model facing recent LHCb and BABAR measurements

Very recently the LHCb experiment released the first measurement of the ratio $R(Λ_c) = {\rm BR}(Λ_b \to Λ_cτ\barν_τ)/{\rm BR}(Λ_b \to Λ_cμ\barν_μ)$. Moreover, the BABAR experiment reported a new result of the leptonic decay ratio of Upsilon meson $Υ(3S)$, namely, $R_{Υ(3S)} = {\rm BR}(Υ(3S) \to τ^+τ^-)/{\rm BR}(Υ(3S) \to μ^+μ^-)$. Both measurements are below their corresponding Standard Model predictions (deficit), deviating by $\sim 1.1σ$ and $\sim 1.8σ$, respectively. Moreover, the LHCb recently presented the first search of the lepton flavor violating decay $B^0 \to K^{\ast 0}μ^\pmτ^\mp$. Motivated by these new data, in this work we study their impact on the phenomenology of the singlet vector leptoquark ($U_1$) model addressing the hints of lepton flavor universality violation in the semileptonic decays of $B$ mesons ($B$ meson anomalies), by carrying out a global fit analysis. In general, we found that a minimal version of the $U_1$ model with a mass of 1.8 TeV can successfully explain the $B$ meson anomalies, while being compatible with all other flavor observables and LHC bounds. Interestingly, our study shows that the new observables $R(Λ_c)$ and $R_{Υ(3S)}$ generate strong tension, leading to non-trivial effects on the global fit. Future improvements at the LHCb and Belle II experiments would help to understand their complementarity. Moreover, we also analyze the impact of the expected sensitivity on flavor observables at Belle II to provide a further test of the $U_1$ model. Finally, we study the minimal assumptions under which the $U_1$ model could, in addition, provide a combined explanation of the anomalous magnetic moment of the muon.

hep-ph↗

arXiv2021

Tests of the Atomki anomaly in lepton pair decays of heavy mesons

The anomalies recently reported in lepton pair transitions of $^8$Be$^*$ and $^4$He nuclei may be attributed to the existence of a feebly interacting light vector boson $X17$. We study the effects of this hypothetical particle in the semileptonic $H^* \to H e^+e^-$ decays ($H$ a $Q\bar{q}$ meson) in the framework of the HQET+VMD model. Using current bounds and the universality assumption of the $X17$ boson to quarks, we find that decays of $D^{*+}$ and $D_s^{*+}$ mesons can be importantly enhanced relative to the dominant photon-mediated contributions. Dedicated experimental searches at current heavy meson factories may confirm the existence of this light boson or set stronger bounds of their couplings to ordinary matter.

hep-ph↗

arXiv2021

Extra gauge bosons and lepton flavor universality violation in $Υ$ and $B$ meson decays

Lepton flavor universality can be tested through the ratio of semileptonic $B$ meson decays and leptonic $Υ$ meson decays, with $Υ\equiv Υ(nS)$ ($n=1,2,3$). For the charged-current transitions $b \to cτ\barν_τ$, discrepancies between the experiment and the Standard Model (SM) have been observed in recent years by different flavor facilities such as BABAR, Belle, and LHCb. While for the neutral-current transitions $b \bar{b} \to τ\barτ$, the BABAR experiment reported recently a new measurement of leptonic decay ratio $R_{Υ(3S)} = {\rm BR}(Υ(3S) \to τ^+τ^-)/{\rm BR}(Υ(3S) \to μ^+μ^-)$, showing an agreement with the SM at the $1.8 σ$ level. In light of this new BABAR result and regarding the connection between new physics (NP) interpretations to the charged-current $b \to c τ\barν_τ$ anomalies and neutral-current $b \bar{b} \to τ\barτ$ processes, in this study, we revisit the NP consequences of this measurement within a simplified model with extra massive gauge bosons that coupled predominantly to left-handed leptons of the third-generation. We show that the BABAR measurement of $R_{Υ(3S)}$ cannot easily be accommodated (within its experimental $1σ$ range) together with the other $b \to cτ\barν_τ$ data, hinting toward a new anomalous observable.

hep-ph↗

arXiv2019

Charged current $b \to c τ\barν_τ$ anomalies in a general $W^\prime$ boson scenario

Very recent experimental information obtained from the Belle experiment, along with that accumulated by the BABAR and LHCb experiments, has shown the existence of anomalies in the ratios $R(D)$ and $R(D^{*})$ associated with the charged-current transition $b \to c τ\barν_τ$. Although the Belle measurements are in agreement with the standard model (SM) predictions, the new experimental world averages still exhibit a tension. In addition, the $D^\ast$ longitudinal polarization $F_L(D^\ast)$ related with the channel $B \to D^\ast τ\barν_τ$ observed by the Belle Collaboration and the ratio $R(J/ψ)$ measured by the LHCb Collaboration also show discrepancies with their corresponding SM estimations. We present a model-independent study based on the most general effective Lagrangian that yields a tree-level effective contribution to the transition $b \to c τ\barν_τ$ induced by a general $W^\prime$ boson. Instead of considering any specific new physics (NP) realization, we perform an analysis by considering all of the different chiral charges to the charm-bottom and $τ$-$ν_τ$ interaction terms with a charged $W^\prime$ boson that explain the anomalies. We present a phenomenological study of parameter space allowed by the new experimental $b \to c τ\barν_τ$ data and with the mono-tau signature $pp \to τ_h X + \rm{MET}$ at the LHC. For comparison, we include some of the $W^\prime$ boson NP realizations that have already been studied in the literature.

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