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Register a new userNew Physics solutions for $brightarrow c,tau,bar{ u}$ anomalies after Moriond 2019
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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.
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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.
Following the updated measurement of the lepton flavour universality (LFU) ratio R_K in B -> Kll decays by LHCb, as well as a number of further measurements, e.g. R_K* by Belle and B_s -> mu mu by ATLAS, we analyse the global status of new physics in b -> s transitions in the weak effective theory at the b-quark scale, in the Standard Model effective theory at the electroweak scale, and in simplified models of new physics. We find that the data continues to strongly prefer a solution with new physics in semi-leptonic Wilson coefficients. A purely muonic contribution to the combination C_9 = -C_10, well suited to UV-complete interpretations, is now favoured with respect to a muonic contribution to C_9 only. An even better fit is obtained by allowing an additional LFU shift in C_9. Such a shift can be renormalization-group induced from four-fermion operators above the electroweak scale, in particular from semi-tauonic operators, able to account for the potential discrepancies in b -> c transitions. This scenario is naturally realized in the simplified U_1 leptoquark model. We also analyse simplified models where a LFU effect in b -> sll is induced radiatively from four-quark operators and show that such a setup is on the brink of exclusion by LHC di-jet resonance searches.
The recent measurements of $R_K$, $B_stomu^+mu^-$, a set of CP-averaged angular observables for the $B^0to K^{*0}mu^+mu^-$ decay, and its isospin partner $B^+to K^{*+}mu^+mu^-$ by the LHCb Collaboration, consistently hint at lepton universality violation in the $bto sellell$ transitions. The so-called $B$ anamolies can be best explained in five one-dimensional scenarios, i.e, $delta C_9^{mu}$, $delta C_{10}^{mu}$, $delta C_L^{mu}$, $delta C_9^{mu}=delta C_{10}^{muprime}$, and $delta C_9^{mu}=-delta C_9^{muprime}$, as demonstrated in recent model independent anlayses~cite{Alok:2019ufo,Alguero:2021anc,Geng:2021nhg,Altmannshofer:2021qrr}. In this work we explore how these scenarios can be distinguished from each other. We show that the combinations of four angular asymmetries $A_i$~$(i=3,4,5,9)$ together with the ratio $R_6$ first proposed in~cite{Jager:2014rwa} can discriminate the five new physics scenarios in proper intervals of $q^2$ and with future high-precision measurements.
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.
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.
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