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Guillermo Baltà

Publications and source records attributed to Guillermo Baltà.

2 recordsLinked to original sources
arXiv2026

New Physics in $ b \to s τ^+τ^-$ Processes and Correlations with $R(D^{(*)})$ and $B\to K^{(*)}ν\barν$: An (SM)EFT Analysis

Tauonic flavour-changing neutral-current transitions ($b\to sτ^+τ^-$) are sensitive probes of New Physics connected to third-generation quarks and leptons. Motivated by the persistent anomalies in $R(D^{(*)})$ and the indications of enhanced $B^+\to K^{+}ν\barν$ rates, we revisit and update the predictions for $b\to sτ^+τ^-$ processes. Building upon a previous work on a data-driven approach to include the dominant $ψ(2S)$ resonances, we provide predictions for $B\to K^{(*)}τ^+τ^-$ ($B_s\toϕτ^+τ^-$) over the full kinematic range. To include possible New Physics contributions within the Weak Effective Theory, we provide semi-analytic expressions for the corresponding branching ratios. We then perform a comprehensive dimension-6 SMEFT analysis of New Physics realised at the TeV scale. We identify regions of parameter space preferred by current data where the branching ratios of $b\to sτ^+τ^-$ processes can be enhanced by several orders of magnitude. While current experimental sensitivities remain far above the SM rates, the enhancements suggested by present flavour data imply that forthcoming limits from LHCb, CMS, and Belle~II will probe significant regions of the relevant SMEFT parameter space. Furthermore, we highlight that while different scenarios can lead to the same predictions for $B\to K^{(*)}ν\barν$ branching ratios, they can be disentangled by measuring $B\to K^{(*)}τ^+τ^-$, $B_s\toτ^+τ^-$ and $B_s\toϕτ^+τ^-$.

hep-ph↗
arXiv2026

Impact of Hadronic Resonances on $B\to K^{(*)}τ^+τ^-$ decays

Neutral-current semileptonic $B$ decays are plagued by hadronic resonances across the dilepton invariant-mass squared spectrum, $q^2$. For light leptons, $\ell=e,μ$, these resonances can be avoided with suitable $q^2$ cuts. This strategy is less straightforward for $τ$ modes, where missing energy from the $τ$ decay makes $q^2$ difficult to reconstruct. In fact, while Belle II is able to discriminate between different regions in $q^2$ due to its clean environment, this is not directly possible in a hadronic one. Therefore, the interpretation of $b\to sτ^+τ^-$ measurements from e.g. LHCb, CMS requires the description of these resonant effects. In this article, we adopt a different strategy by including the resonant contributions (in particular from $ψ(2S)$) into our predictions for $B\to K^{(*)}τ^+τ^-$ decays, instead of avoiding them. We provide predictions for different initial kinematic points ($4m_τ^2, 14.18\,$GeV$^2$ and $15\,$GeV$^2$) that can be convenient for LHCb, CMS and Belle II. For this, we use a data-driven approach based on the LHCb measurements of $B\to K^{(*)}μ^+μ^-$ decays. Including the resonances and integrating over the full $q^2$ range substantially enhances the Standard Model predictions. However, for sufficiently large New Physics, motivated by the current tensions in $R(D^{(*)})$ and $B\to K^{(*)}νν$ decays, the short-distance contribution becomes comparable to or even exceeds the resonant one. This highlights two advantages of this strategy: it exploits the additional phase space associated with the resonant regions to probe large New Physics contributions, and it enables the use of hadron-collider data, where the resonances cannot be resolved. We further quantify how including or neglecting the resonances affects the total branching ratio as a function of New Physics contributions and, equivalently, of the experimental precision.

hep-ph↗