Global fit to $b\to c\tau \nu$ anomalies 2022 mid-autumn

Abstract

Recently, the LHCb collaboration announced a preliminary result of the test of lepton flavor universality (LFU) in $B\to D^{(\ast )}$ semi-leptonic decays: $R_D^{LHCb2022}=0.441\pm 0.089$ and $R_{D^{\ast }}^{LHCb2022}=0.281\pm 0.030$ based on the LHC Run 1 data. This is the first result of $R_D$ for the LHCb experiment, and its precision is comparable to the other $B$-factory data. Interestingly, those data prefer the violation of the LFU again. A new world average of the data from the BaBar, Belle, and LHCb collaborations is $R_D=0.358\pm 0.027$ and $R_{D^{\ast }}=0.285\pm 0.013$. Including this new data, we update a circumstance of the $b\to c\tau \overline{\nu }$ measurements and their implications for new physics. Incorporating recent developments for the $B\to D^{(\ast )}$ form factors in the Standard Model (SM), we observe a $4.1\sigma$ deviation from the SM predictions. Our updates also include; model-independent new physics (NP) formulae for the related observables; and the global fittings of parameters for leptoquark scenarios as well as single NP operator scenarios. Furthermore, we show future potential to indirectly distinguish different new physics scenarios with the use of the precise measurements of the polarization observables in $B\to D^{(\ast )}\tau \overline{\nu }$ at the Belle II and the high-$p_{\mathrm{T}}$ flavored-tail searches at the LHC. We also discuss an impact on the LFU violation in ${\rm Y}\to l^{+}{l}^{-}$.

Comments: 38 pages, 5 figures, 6 Tables; v2: references added; v3: all experimental data are up-to-date, equivalent to arXiv:2405.06062v1; v4: restoring arXiv:2210.10751v2