B -meson charged current anomalies: The post-Moriond 2019 status

Abstract

In this note, we discuss the impact of the recent Belle result on the various theoretical explanations of the RD and RD * anomalies. The pure tensor explanation, which was strongly disfavoured by the measurements of F D * L and high-pT p p → τ ν searches before Moriond, is now completely allowed because of reduction of the experimental world-average. Moreover, the pure right-chiral vector solution (involving right-chiral neutrinos) has now moved into the 2σ allowed range of the LHC p p → τ ν searches. We also critically re-examine the bound on B(B − c → τ −ν τ ) from LEP data and show that the bound is considerably weaker than the number 10% often used in the recent literature.The Belle collaboration has recently published results for R D and R D * with a semileptonic tag [1,2], and their result is consistent with the Standard Model (SM) expectation within 1.2σ. Consequently, the experimental world average has moved towards the SM. However, the tension between the experimental world average and the SM expectation is still more than 3σ, and thus, it is interesting to re-examine the status of the various New Physics (NP) explanations in view of the new worldaverage. In Table. I below, we collect all the experimental results related to this anomaly. SM prediction Measurement04 [6] −0.38 +0.55 −0.53 [9, 10] F D * L 0.46 ± 0.04 0.60 ± 0.087 [11] R J/ψ 0.290 0.71 ± 0.25 [12] TABLE I. Observables, their SM predictions and the experimentally measured values. The pre-Moriond experimental averages for RD and RD * are based on [9, 10, 13-19].The most general effective Lagrangian for the decay b → c τ −ν τ involving mass dimension-6 operators and only left-chiral neutrinos can be written asc. If one uses power-counting rules arising from linearlyrealised SU(2) × U(1) gauge invariance, it turns out that the Wilson Coefficient (WC) C RL V , with the possibility of lepton non-universality, is only generated at the mass dimension-8 level [20]. Thus, it is expected to be suppressed compared to the other WCs as long as the scale * bardhan@post.bgu.ac.il † diptimoy.ghosh@iiserpune.ac.in of NP is not too close to the Higgs vacuum expectation value, thus we will ignore it in this analysis. If one also assumes the existence of light right-chiral neutrino(s), as was first done in [21] to solve the R D anomaly, five additional operators can be constructed by the replacement P L → P R in the leptonic currents of Eq. 1. In particular, a pure-right chiral vector current namely,was considered by several authors [22][23][24] , and we will include it in our analysis. As the experimental situation for R D and R D * is far from clear, we do not try to perform a fit to the WCs; for an early global fit, see [25]. Instead, we show how R D and R D * vary with respect to the WCs, and overlay the current 1σ experimental world-average and the corresponding currently allowed values of the WCs.In Fig. 1, we show this for two WCs C LL V and C RR V assuming them to be real. It can be seen from the left 0.20 0.25 0.30 0.35 0.40 0.45 R D 0.90 0.95 1.00 1.05...

R2 as a single leptoquark solution to RD(*Попов1, Schmidt2, White3 2019Phys. Rev. D701430View full textAdd to dashboardCite

“…Figure 5 in Ref. [97], in particular, shows this dependency where a bound of 10% corresponds to f c =f u ∼ 4 × 10 −3 and the most liberal bound of 60% corresponds to a ratio that is a factor of 5 smaller, f c =f u ∼ 8 × 10 −4 . Reference [97] use PYTHIA8 [98,99], which relies on experimental data to tune hadronization, to estimate the hadronization fraction and derive a fairly liberal lower bound of 39%.…”

“…Several groups inferred limits on BRðB c → τνÞ < ½0.1; 0.6 [52,83,86,96,97] via different theoretical arguments. In the top right panel of Fig.…”

“…However, there is some controversy over this constraint that relies on the probability that a bottom quark hadronizes with a charmed quark that has not yet been measured at the LHC. There is currently an ongoing discussion on how the probability at the LHC can be inferred from LEP measurements and Monte Carlo simulations, where the authors of the first paper [83,87] advocate values in the range 10%-20% compared to some recent papers that advocate liberal constraints in the range 39%-60% [96,97]. The large range of values comes from the fact that the limit is quite sensitive to the ratio of hadronization probabilities f c =f u , that is, the probability of hadronizing with a charm or up quark, respectively.…”

Charged current b→cτν¯τ anomalies in a general W′ boson scenario

“…the new Belle measurements, see Refs. [33][34][35][36][37]) 1 . On the other hand, particular NP scenarios such as: charged scalars [46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62], leptoquarks (both scalar and vector) , extra gauge bosons [47,94,[98][99][100][101][102][103][104][105][106][107][108][109][110][111], right-handed neutrinos [62,[106][107][108][109][110][111][112][113], R-parity violating (RPV) supersymmetric couplings [31,[114][115]…”

A near-minimal leptoquark model for reconciling flavour anomalies and generating radiative neutrino masses

“…Together these measurements amount to a deviation 3σ [35,37] from SM predictions, which can be significantly reduced in the presence of new physics [36][37][38][39][40].…”