[Paper Review] An in-depth analysis of $b o c(s)$ semileptonic observables with possible $μ- τ$ mixing

Srimoy Bhattacharya, Aritra Biswas+2 more|arXiv (Cornell University)|Feb 7, 2019

Particle physics theoretical and experimental studies4 citations

TL;DR

This paper reanalyzes a minimal model of new physics that explains both $b \to c(s)$ semileptonic flavor anomalies—$R(D^{(*)})$ and $R(K^{(*)})$—via $\mu$-$\tau$ mixing in the lepton sector. Using 170 observables including updated experimental data and theoretical constraints, it finds a $3.78\sigma$ global tension and provides a precise new calculation of $R(J/\Psi)$, confirming the model's viability with improved statistical significance.

ABSTRACT

In a couple of recent publications ( arXiv:1706.08437 and arXiv:1712.01593 ), the authors attempted to achieve simultaneous explanation of the persistent flavor anomalies in $b o s$ and $b o c$ semileptonic decays with a minimal scheme by using only three unknown new parameters. The analysis was obtained with a handful of precise observables. Motivated by their proposal, in this paper we reanalyze the models proposed in the aforementioned papers with a total of 170 observables from those channels including newly available measurements, correlated theoretical results, and constraints. We validate our results by searching for the most influential points and outliers. By analyzing the parameter spaces and their relationship with the constraints, we gain new insight and statistical significance in those models. We also provide a new and precise calculation of $R(J/Ψ)$, obtained during the analysis.

Motivation & Objective

• To reevaluate a minimal new physics model that explains both $R(D^{(*)})$ and $R(K^{(*)})$ anomalies using only three new parameters.
• To test the model's consistency with a comprehensive dataset of 170 observables from $b\to c(s)$ semileptonic decays, including recent measurements and theoretical constraints.
• To identify influential points and outliers to validate the model's robustness and statistical significance.
• To provide a new, precise calculation of $R(J/\Psi)$ within the model framework.

Proposed method

• The authors use a global fit framework incorporating 170 experimental and theoretical observables from $b\to c(s)$ semileptonic decays, including $R(D^{(*)})$, $R(K^{(*)})$, and $R(J/\Psi)$.
• They apply a minimal extension of the Standard Model with $\mu$-$\tau$ mixing, introducing three new parameters to explain lepton flavor universality violation.
• The effective Hamiltonian is derived for $b\to c\tau\bar{\nu}$ and $b\to s\mu\bar{\mu}$ transitions, with Wilson coefficients $C_9^{NP}$, $C_{10}^{NP}$, and $C^{NP}$ expressed in terms of model parameters $A_1$, $A_2$, $A_3$, $A_5$.
• The model is tested via a statistical analysis of parameter space, identifying key constraints and outliers to assess robustness.
• The calculation of $R(J/\Psi)$ is performed using the same framework, yielding a new, precise value within the model.
• The global significance of the anomalies is quantified as $3.78\sigma$ when combining $R(D)$ and $R(D^*)$ deviations.

Experimental results

Research questions

• RQ1 Can a minimal model with $\mu$-$\tau$ mixing simultaneously explain the $R(D^{(*)})$ and $R(K^{(*)})$ anomalies with only three new parameters?
• RQ2 How do the updated experimental measurements and theoretical constraints affect the viability of the model?
• RQ3 What is the statistical significance of the combined $b\to c$ and $b\to s$ anomalies within this model?
• RQ4 How does the model predict $R(J/\Psi)$, and how does it compare to experimental data?
• RQ5 Which parameters or observables are most influential in constraining the model space?

Key findings

• The model achieves a consistent explanation of both $R(D^{(*)})$ and $R(K^{(*)})$ anomalies with only three new parameters, supporting its minimality.
• The global significance of the combined $b\to c$ and $b\to s$ anomalies reaches $3.78\sigma$, reinforcing the case for new physics.
• The analysis identifies key observables and outliers that significantly influence the parameter space, enhancing model validation.
• A new, precise calculation of $R(J/\Psi)$ is obtained, consistent with the model's predictions and available data.
• The parameter space is constrained by correlations between $C_9^{NP}$, $C_{10}^{NP}$, and $C^{NP}$, with $\mu$-$\tau$ mixing playing a central role.
• The model remains viable under stringent constraints from both experimental and theoretical inputs, with no major inconsistencies found.