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Register a new userMaximizing the Impact of New Physics in $brightarrow c tau u$ Anomalies
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We develop a rigorous, semi-analytical method for maximizing any $bto ctau u$ observable in the full 20-real-dimensional parameter space of the dimension 6 effective Hamiltonian, given some fixed values of $R_{D^{(*)}}$. We apply our method to find the maximum allowed values of $F^L_{D^*}$ and $R_{J/psi}$, two observables which have both come out higher than their SM predictions in recent measurements by the Belle and LHCb collaborations. While the measurements still have large error bars, they add to the existing $R_{D^{(*)}}$ anomaly, and it is worthwhile to consider NP explanations. It has been shown that none of the existing, minimal models in the literature can explain the observed values of $F^L_{D^*}$ and $R_{J/psi}$. Using our method, we will generalize beyond the minimal models and show that there is no combination of dimension 6 Wilson operators that can come within $1sigma$ of the observed $R_{J/psi}$ value. By contrast, we will show that the observed value of $F^L_{D^*}$ can be achieved, but only with sizable contributions from tensor and mixed-chirality vector Wilson coefficients.
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At Moriond 2019, Belle collaboration has announced new measurements on the flavour ratios $R_D - R_{D^*}$ which are consistent with their Standard Model predictions within $1.2sigma$. After inclusion of these measurements, the global tension in $R_D - R_{D^*}$ has reduced from $4.1sigma$ to $3.1sigma$ which is still significant. The measurements of these ratios indicate towards the violation of lepton flavor universality in $brightarrow c,l,bar{ u}$ decay. Assuming new physics in $brightarrow c,tau,bar{ u}$ transition, we have done a global fit to all available data in this sector to identify the allowed new physics solutions. We find that there are seven allowed new physics solutions which can account for all measurements in $brightarrow c,tau,bar{ u}$ transition. We show that a simultaneous measurement of the $tau$ polarization fraction and forward-backward asymmetry in $Brightarrow D,tau,bar{ u}$, the zero crossing point of forward backward asymmetry in $Brightarrow D^*taubar{ u}$ and the branching ratio of $B_crightarrow tau,bar{ u}$ decay can distinguish these seven new physics solutions if they can be measured with a required precision.
In this addendum to arXiv:1811.09603 we update our results including the recent measurement of ${cal R}(D)$ and ${cal R}(D^*)$ by the Belle collaboration: ${cal R}(D)_{rm Belle} = 0.307pm0.037pm0.016$ and ${cal R}(D^*)_{rm Belle}=0.283pm0.018pm0.014$, resulting in the new HFLAV fit result ${cal R}(D) = {0.340pm0.027 pm 0.013}$, ${cal R}(D^*) = {0.295pm0.011 pm 0.008 }$, exhibiting a $3.1,sigma$ tension with the Standard Model. We present the new fit results and update all figures, including the relevant new collider constraints. The updated prediction for ${cal R}(Lambda_c)$ from our sum rule reads ${cal R}(Lambda_c)= mathcal{R}_{rm SM}(Lambda_c) left( 1.15 pm 0.04 right) = 0.38 pm 0.01 pm 0.01$. We also comment on theoretical predictions for the fragmentation function $f_c$ of $bto B_c$ and their implication on the constraint from $B_{u/c}totau u$ data.
A number of observables related to the $b to s l^+ l^-$ transition show deviations from their standard model predictions. A global fit to the current $brightarrow sl^+l^-$ data suggests several new physics solutions. Considering only one operator at a time and new physics only in the muon sector, it has been shown that the new physics scenarios (I) $C_9^{rm NP}<0$, (II) $C_{9}^{rm NP} = -C_{10}^{rm NP}$, (III) $C_9^{rm NP} = -C_9^{prime rm NP}$ can account for all data. In this paper, we develop a procedure to discriminate between these scenarios through a study of the branching ratio of $B_s to mu^+mu^-$ and the distribution of $Bto K^*mu^+mu^-$ decay in the azimuthal angle. The scenario II predicts a significantly lower value of $mathcal{B}(B_sto mu^+mu^-)$ and can be distinguished from the other two scenarios if the experimental uncertainty comes down by a factor of three. On the other hand, a precise measurement of the CP averaged angular observables $S_3$ and $S_9$ in high $q^2$ bin of $Bto K^*mu^+mu^-$ decay can uniquely discriminate between the other two scenarios. We define two azimuthal angle asymmetries, proportional to $S_3$ and to $S_9$ respectively, which can be measured with small statistical uncertainty.
The combined analysis of the BaBar, Belle, and LHCb data on $Bto Dtau u$, $Bto D^*tau u$ and $B_cto J/Psitau u$ decay observables shows evidence of physics beyond the Standard Model (SM). In this article, we study all the one- and two-dimensional scenarios which can be generated by adding a single new particle to the SM. We put special emphasis on the model-discriminating power of $F_L(D^*)$ and of the $tau$ polarizations, and especially on the constraint from the branching fraction ${rm BR}(B_ctotau u)$. We critically review this constraint and do not support the aggressive limit of ${rm BR}(B_ctotau u)<10%$ used in some analyses. While the impact of $F_L(D^*)$ is currently still limited, the ${rm BR}(B_ctotau u)$ constraint has a significant impact: depending on whether one uses a limit of $60%$, $30%$ or $10%$, the pull for new physics (NP) in scalar operators changes drastically. More specifically, for a conservative $60%$ limit a scenario with scalar operators gives the best fit to data, while for an aggressive $10%$ limit this scenario is strongly disfavored and the best fit is obtained in a scenario in which only a left-handed vector operator is generated. We find a sum rule for the branching ratios of $Bto Dtau u$, $Bto D^*tau u$ and $Lambda_bto Lambda_ctau u$ which holds for any NP contribution to the Wilson coefficients. This sum rule entails an enhancement of ${rm BR}(Lambda_bto Lambda_ctau u)$ over its SM prediction by $(24pm 6)%$ for the current $mathcal{R}(D^{(*)})$ data.
In this article, we have predicted the standard model (SM) values of the asymmetric and angular observables in $Bto D^{(ast)}tau u_{tau}$ decays, using the results of the new up-to-date analysis in $Bto D^{(*)}ell u_{ell}$. We have also revisited the SM prediction of the inclusive ratio $mathcal{R}_{X_c}$, and have given its values in different schemes of the charm quark mass. This is the first analysis which includes all the known corrections in the SM. In addition, we have analysed the $bto ctau u_tau$ decay modes in a model-independent framework of effective field theory beyond the standard model. Considering all the possible combinations of the effective operators in $b to c tau u_{tau}$ decays and using the Akaike Information Criterion, we find out the scenarios which can best explain the available data on these channels. In the selected scenarios, best-fit values and correlations of the new parameters are extracted. Using these results, predictions are made on various observables in the exclusive and inclusive semitaunic $b to c $ decays. The graphical correlations between these observables are shown, which are found to be useful in discriminating various new physics scenarios.
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