Confronting lepton flavor universality violation in B decays with high-$p_T$ tau lepton searches at LHC (1609.07138v1)

Abstract: We confront the indications of lepton flavor universality (LFU) violation observed in semi-tauonic $B$ meson decays with new physics (NP) searches using high $p_T$ tau leptons at the LHC. Using effective field theory arguments we correlate possible non-standard contributions to semi-tauonic charged currents with the $\tau^+ \tau^-$ signature at high energy hadron colliders. Several representative standard model extensions put forward to explain the anomaly are examined in detail: (i) weak triplet of color-neutral vector resonances, (ii) second Higgs doublet and (iii) scalar or (iv) vector leptoquark. We find that, in general, $\tau^+ \tau^-$ searches pose a serious challenge to NP explanations of the LFU anomaly. Recasting existing 8 TeV and 13 TeV LHC analyses, stringent limits are set on all considered simplified models. Future projections of the $\tau^+ \tau^-$ constraints as well as caveats in interpreting them within more elaborate models are also discussed.

• The paper examines potential new physics explanations for lepton flavor universality violation in B decays using effective field theory and simplified models constrained by LHC data.
• The study recasts existing LHC high-pT tau-pair searches, applying them to new physics models to derive stringent constraints on viable explanations for the R(D*) anomaly.
• It emphasizes the importance of LHC high-pT searches for constraining new physics in B decays and provides theoretical groundwork for future experimental strategies.

Theoretical Analysis of Lepton Flavor Universality Violation in B Decays

The paper examines potential lepton flavor universality (LFU) violations in B meson decays, with specific emphasis on the role of high-$p_T$ tau lepton signatures at the Large Hadron Collider (LHC). This research investigates deviations from the expected LFU in semi-tauonic B decays, prompting a deep dive into new physics (NP) theories as potential explanations for these anomalies. This analysis is carried out using effective field theory (EFT) frameworks and simplified models that suggest non-standard contributions to charged currents, potentially detectable via high energy hadron collider processes like those at the LHC.

Key Insights and Methodology

The authors propose linking these LFU anomalies to potential NP by examining the correlation between semi-tauonic charged currents and high-energy tau pairs at the LHC. They explore extensions to the Standard Model (SM) that have been posited as explanations for these anomalies. These include models featuring a weak triplet of color-neutral vector resonances, a second Higgs doublet, and scalar or vector leptoquarks. They employ EFT to outline how new massive particles might affect low-energy processes, particularly focusing on generating operators that respect the SM gauge symmetry.

A detailed examination of simplified NP models is conducted, specifically considering their ability to meet constraints from both low-energy and high-energy collider data. The models are investigated for the presence of additional charged or colored states that could interact with third-generation SM fermions, offering insights into potential signals for LFU violation.

Numerical Results and Constraints

This paper's numerical analysis recasts existing LHC $\tau^+\tau^-$ searches (from both 8 TeV and 13 TeV data sets), applying them to their NP models. These analyses yield stringent limits on all considered model extensions. For instance, the work demonstrates that viable NP explanations of the $R(D^{(*)})$ anomaly are tightly constrained by existing LHC data, particularly demanding significant couplings between NP states and tau leptons.

The paper concludes that general NP solutions to LFU anomalies involve significant theoretical and experimental challenges, especially when coupled with high-$p_T$ tau signatures at the LHC. Future projections suggest that ongoing and upcoming LHC analyses will further refine these constraints, shedding additional light on the potential for NP beyond the SM.

Implications and Future Directions

The implications of this paper are twofold: First, it reinforces the utility of LHC high-$p_T$ searches in exploring possible LFU violations and NP in B decays. Second, it offers substantial theoretical groundwork to inform future experimental strategies, highlighting the need for both precise collider searches and advancements in EFT methodologies.

Looking forward, the paper opens several avenues for further research. It speculates on expanded LHC search strategies that could account for broader classes of NP models, perhaps involving interactions beyond simple extensions of third-generation couplings. Additionally, it encourages enhanced theoretical formulations that could confront or complement alternative routes to explain lepton flavor universality violations. Through such efforts, the paper enhances the collaborative bridge between theory and experiment in the search for NP in particle physics.