arXiv subjects

Marxil Sánchez

Publications and source records attributed to Marxil Sánchez.

3 recordsLinked to original sources

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗