arXiv subjects

Arianna Tinari

Publications and source records attributed to Arianna Tinari.

9 recordsLinked to original sources

arXiv2026

Constraints on lepton-flavor mixing with third-generation new physics

We study the implications of an approximate $U(2)^5$ flavor symmetry at the TeV scale, under the assumption of new physics predominantly coupled to the third-generation fermions, focusing on the breaking of the $U(2)_\ell$ subgroup governing the mixing between second- and third-generation left-handed leptons. We derive constraints on the corresponding spurion parameter $δ$ from current data on lepton flavor violating (LFV) and lepton flavor universality (LFU) observables, finding that $R_{K^{(*)}}$ and $\mathcal{B}(B_s \to μμ)$ give the most stringent bound on $δ$, yielding ${|δ|<0.051}$ at 95% CL. In addition, we provide updated bounds for LFV decay rates and discuss prospects for future sensitivity improvements, finding that future LFV searches could further tighten constraints on the mixing between second- and third-generation leptons.

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arXiv2026

Disentangling short- vs. long-distance dynamics in $B\to K^{*}μ^+μ^-$

We present an updated data-driven analysis of short- vs. long-distance dynamics in $B\to K^{*}μ^+μ^-$. The analysis is based on the recent LHCb measurement of the full angular distribution of this process, taking advantage of the previously published global amplitude fit. Thanks to the precise di-lepton invariant-mass binning and angular observables directly sensitive to absorptive phases, current data provide novel insights into non-local contributions. We analyze the latter using a dispersive description, whose free parameters are determined via the amplitude fit. The dispersive model provides a satisfactory overall description of current data, without the need to introduce additional ad hoc hadronic parameters. The extracted value of the short-distance coefficient $C_9$ is lower than its Standard Model prediction, but significantly closer to it than in analyses where long-distance contributions are not constrained by data. The overall tension with the SM does not exceed the $2σ$ level. We also obtain precise postdictions for the angular observables $S_{7,8,9}$, and envisage novel consistency tests among them. In view of future, more precise data, these could provide valuable tests of the description of non-local effects in this process that, if further validated, would enable an even more robust extraction of short-distance information.

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arXiv2025

Charm rescattering in $B^0\to K^0\bar{\ell}\ell$: an improved analysis

We improve upon previous explicit estimates of charm rescattering contributions to the decay $B^0\to K^0\bar{\ell}\ell$ by including contributions from dipole interactions with the intermediate charm-meson states, and by further investigating the structure of the electromagnetic form factors. Using a model of fundamental meson fields inspired by heavy-hadron chiral perturbation theory, augmented by form factors motivated by theoretical considerations as well as experimental data, we provide a thorough investigation of rescattering contributions induced by intermediate $D^{(*)}D^{(*)}_s$ states.

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arXiv2025

Theoretical Aspects of $b \to s \bar{\ell}\ell$ Decays

Flavor-changing neutral current decays such as $b \to s \bar{\ell} \ell$ are highly suppressed in the Standard Model (SM) and therefore provide sensitive tests for new physics. Persistent tensions between SM predictions and experimental results in branching ratios and angular observables can be explained by a shift of the Wilson coefficient $C_9$ of the effective operator $O_9$ by $\sim 20 \%$ relative to the SM value. This shift could arise from a non-standard short-distance contribution or from an inaccurate description of long-distance dynamics, particularly charm rescattering contributions. We therefore investigate charm rescattering contributions in $B^0 \to K^0 \bar{\ell}\ell$ using a model of fundamental hadronic degrees of freedom inspired by heavy-hadron chiral perturbation theory and improved by appropriate form factors as well as experimental data. Our analysis shows that such effects, with a high degree of fine-tuning, could shift $C_9$ by $\sim 20\%$, at the cost of introducing a more pronounced $q^2$ dependence, whereas experimental data are consistent with a $q^2$-independent shift of $C_9$ with the current experimental uncertainties. In the most natural scenario, we find these effects to be of the order of $\sim 5\%$. Connections with other flavor anomalies further illustrate the strong discovery potential of $b \to s \bar{\ell} \ell$ modes.

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arXiv2025

Explicit estimate of charm rescattering in $B^0 \to K^0 \bar{\ell} \ell$

We analyze $B^0 \to K^0 \bar{\ell}\ell$ long-distance contributions induced by the rescattering of a pair of charmed and charmed-strange mesons. We present an explicit estimate of these contributions using an effective description in terms of hadronic degrees of freedom, supplemented by data on the $B^0 \to D^*D_s (D^*_sD)$ transition in order to reproduce the corresponding discontinuity in the $B^0 \to K^0 \bar{\ell}\ell$ amplitude. The $D^* D_s (D^*_s D) K$ vertex is estimated using heavy-hadron chiral perturbation theory, obtaining an accurate description of the whole rescattering process in the low-recoil (or high-$q^2$) limit. We also present an extrapolation to the whole kinematical region introducing hadronic form factors. The explicit estimate of the leading $D^*D_s (D^*_sD)$ intermediate state leads to a long-distance amplitude which does not exceed a few percent relative to the short-distance one. The consequences of this result for the extraction of the short-distance coefficient $C_9$ are discussed.

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arXiv2024

Short- vs Long-Distance Dynamics in $b \rightarrow s\bar{\ell} \ell$ Decays

The tension of $B\to K^{(*)}\bar\ell\ell$ decays with the Standard Model (SM) can be attributed to a short-distance (SD) $b s\bar\ell\ell$ interaction. We show two methods to disentangle this effect from long-distance (LD) dynamics. Firstly, we perform a comparison of the inclusive $b\to s\bar\ell\ell$ rate at high $q^2=m^2_{\ell\ell}\geq 15~\rm GeV^2$ with a determination based on data on the leading exclusive modes, finding a $\sim 2σ$ discrepancy. Secondly, we analyze the exclusive $B\to K^{(*)}\bar\ell\ell$ spectrum in the entire $q^2$ region. With a dispersive parametrization of the charmonia resonances, we extract the non-SM contribution to the Wilson coefficient $C_9$ for every bin in $q^2$. The result is compatible with the SD hypothesis and the inclusive determination. Finally, with the aim of having better control over LD effects that mimic the $C_9$ contribution, we estimate the size of a few charm-rescattering processes in $B\to K\bar\ell\ell$.

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arXiv2024

Short- vs. long-distance physics in $B\to K^{(*)} \ell^+\ell^-$: a data-driven analysis

We analyze data on $B\to Kμ^+μ^-$ and $B\to K^*μ^+μ^-$ decays in the whole dilepton invariant mass spectrum with the aim of disentangling short- vs. long-distance contributions. The sizable long-distance amplitudes from $c \bar{c}$ narrow resonances are taken into account by employing a dispersive approach. For each available $q^2=m_{μμ}^2$ bin and each helicity amplitude an independent determination of the Wilson coefficient $C_9$, describing $b\to s\ell^+\ell^-$ transitions at short distances, is obtained. The consistency of the $C_9$ values thus obtained provides an a posteriori check of the absence of additional, sizable, long-distance contributions. The systematic difference of these values from the Standard Model expectation supports the hypothesis of a non-standard $b\to s μ^+μ^-$ amplitude of short-distance origin.

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arXiv2023

Semi-inclusive $b\to s\bar{\ell}\ell$ transitions at high $q^2$

We present an updated Standard Model (SM) estimate of the inclusive $b\to s\bar{\ell}\ell$ rate at high dilepton invariant mass ($q^2\geq 15~{\rm GeV}^2$). We show that this estimate is in good agreement with the result obtained summing the SM predictions for the leading one-body modes ($K$ and $K^*$) and the subleading non-resonant $Kπ$ channel (for which we also present an updated estimate). On the contrary, the semi-inclusive sum based on data exhibits a deficit compared to the inclusive SM prediction in the muon modes. The statistical significance of this deficit does not exceed $2σ$, but is free from uncertainties on hadronic form factors, and fully compatible with the deficit observed at low-$q^2$ on the exclusive modes. The implications of these results in conjunction with other SM tests on $b\to s\barμμ$ modes are briefly discussed.

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arXiv2023

New tests of short-distance dynamics in $b \rightarrow s\bar{\ell} \ell$ decays

The rare $B \to K^{(*)} \bar{\ell} \ell$ decays exhibit a long-standing tension with Standard Model (SM) predictions, which can be attributed to a lepton-universal short-distance $b \to s \bar{\ell} \ell$ interaction. We present two novel methods to disentangle this effect from long-distance dynamics: one based on the determination of the inclusive $b \to s \bar{\ell} \ell$ rate at high dilepton invariant mass ($q^2\geq 15~{\rm GeV}^2$), the other based on the analysis of the $q^2$ spectrum of the exclusive modes $B \to K^{(*)} \bar{\ell} \ell$ (in the entire $q^2$ range). Using the first method, we show that the SM prediction for the inclusive $b \to s \bar{\ell} \ell$ rate at high dilepton invariant mass is in good agreement with the result obtained summing the SM predictions for one- and two-body modes ($K$, $K^*$, $Kπ$). This observation allows us to perform a direct comparison of the inclusive $b \to s \bar{\ell} \ell$ rate with data. This comparison shows a significant deficit ($\sim 2σ$) in the data, fully compatible with the deficit observed at low-$q^2$ on the exclusive modes. This provides independent evidence of an anomalous $b \to s \bar{\ell} \ell$ short-distance interaction, free from uncertainties on the hadronic form factors. To test the short-distance nature of this effect we use a second method, where we analyze the exclusive $B \to K^{(*)} \bar{\ell} \ell$ data in the entire $q^2$ region. Here, after using a dispersive parametrization of the charmonia resonances, we extract the non-SM contribution to the universal Wilson coefficient $C_9$ for every bin in $q^2$ and for every polarization. The $q^2$- and polarization-independence of the result, and its compatibility with the inclusive determination, provide a consistency check of the short-distance nature of this effect.

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