Measurement of an Excess of B -> D(*) Tau Nu Decays and Implications for Charged Higgs Bosons

Abstract: Based on the full BaBar data sample, we report improved measurements of the ratios R(D()) = B(B -> D() Tau Nu)/B(B -> D() l Nu), where l is either e or mu. These ratios are sensitive to new physics contributions in the form of a charged Higgs boson. We measure R(D) = 0.440 +- 0.058 +- 0.042 and R(D) = 0.332 +- 0.024 +- 0.018, which exceed the Standard Model expectations by 2.0 sigma and 2.7 sigma, respectively. Taken together, our results disagree with these expectations at the 3.4 sigma level. This excess cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model. Kinematic distributions presented here exclude large portions of the more general type III two-Higgs-doublet model, but there are solutions within this model compatible with the results.

• The paper refines measurements of R(D) and R(D*), showing deviations from the Standard Model with a combined 3.4σ discrepancy.
• The analysis reports R(D)=0.440±0.058±0.042 and R(D*)=0.332±0.024±0.018, underscoring potential new physics.
• Results counter simple charged Higgs models and suggest viable extensions in a general type III 2HDM framework.

Measurement of an Excess of $\overline{B}\to D^{(*)}\tau^-\overline{\nu}_\tau$ Decays and Implications for Charged Higgs Bosons

The paper under review presents a thorough analysis of the full BaBar data set to report refined measurements of the ratios ${\cal R}(D)$ and ${\cal R}(D^*)$. These ratios are defined as the branching fractions of $\overline{B}$ meson decays to $D\tau^-\overline{\nu}_\tau$ and $D^*\tau^-\overline{\nu}_\tau$, normalized to the decays into lighter leptons, specifically electrons or muons. The purpose of these measurements is to explore the potential presence of new physics beyond the Standard Model, specifically the contribution of a charged Higgs boson.

The results yielded by this study indicate values for ${\cal R}(D) = 0.440 \pm 0.058 \pm 0.042$ and ${\cal R}(D^*) = 0.332 \pm 0.024 \pm 0.018$. These findings display significant deviations from the predictions made by the Standard Model, quantified as $2.0\sigma$ and $2.7\sigma$ for ${\cal R}(D)$ and ${\cal R}(D^*)$, respectively. When combined, these deviations culminate in a $3.4\sigma$ discrepancy from the expected Standard Model values.

The study further explores the implications of these results concerning models with extended Higgs sectors. Specifically, in the context of a type II two-Higgs-doublet model (2HDM), the observed excess cannot be adequately accounted for by introducing a charged Higgs boson. Nevertheless, analyses of kinematic distributions presented in the study demonstrate that while substantial areas of the parameter space in the more general type III 2HDM can be dismissed, there remain viable solutions within this model that align with the experimental outcomes observed.

The implications of these findings are significant for both theoretical and experimental physics. Practically, they prompt a reevaluation of current models and rekindle interest in exploring Higgs-related extensions to the Standard Model. Furthermore, the deviations observed suggest potential new physics interactions that could, in principle, provide explanations for other anomalies or unanswered questions in particle physics. Future advancements might focus on more refined theoretical models or alternative experimental setups to either confirm the excess or provide higher precision measurements that can further constrain or rule out potential new physics contributions.

Given these results, the field must continue to engage with enhanced experimental techniques or refined model frameworks to substantiate or nullify the present deviations. Continued investigations in this area may also illuminate pathways toward understanding other unresolved problems in particle physics, such as flavor physics and CP violations. Ultimately, this research exemplifies the intricate interplay between theory and experiment that is vital in the quest to expand the fundamental understanding of particle physics.