# $D^*$ polarization vs. $R_{D(*)}$ anomalies in the leptoquark models

Iguro, Syuhei; Kitahara, Teppei; Watanabe, Ryoutaro; Yamamoto, Kei (2018). $D^*$ polarization vs. $R_{D(*)}$ anomalies in the leptoquark models. TTP 37, University of Zurich.

## Abstract

Polarization measurements in B¯→D(∗)τν¯¯¯ are useful to check consistency in new physics explanations for the RD and RD∗ anomalies. In this paper, we investigate the D∗ and τ polarizations and focus on the new physics contributions to the fraction of a longitudinal D∗ polarization (FD∗L), which is recently measured by the Belle collaboration FD∗L=0.60±0.09, in model-independent manner and in each single leptoquark model (R2, S1 and U1) that can naturally explain the RD(∗) anomalies. It is found that B(B+c→τ+ν) severely restricts deviation from the Standard Model (SM) prediction of FD∗L,SM=0.46±0.04 in the leptoquark models: [0.43, 0.44], [0.42, 0.48], and [0.43, 0.47] are predicted as a range of FD∗L for the R2, S1, and U1 leptoquark models, respectively, where the current data of RD(∗) is satisfied at 1σ level. It is also shown that the τ polarization observables can much deviate from the SM predictions. The Belle II experiment, therefore, can check such correlations between RD(∗) and the polarization observables, and discriminate among the leptoquark models.

## Abstract

Polarization measurements in B¯→D(∗)τν¯¯¯ are useful to check consistency in new physics explanations for the RD and RD∗ anomalies. In this paper, we investigate the D∗ and τ polarizations and focus on the new physics contributions to the fraction of a longitudinal D∗ polarization (FD∗L), which is recently measured by the Belle collaboration FD∗L=0.60±0.09, in model-independent manner and in each single leptoquark model (R2, S1 and U1) that can naturally explain the RD(∗) anomalies. It is found that B(B+c→τ+ν) severely restricts deviation from the Standard Model (SM) prediction of FD∗L,SM=0.46±0.04 in the leptoquark models: [0.43, 0.44], [0.42, 0.48], and [0.43, 0.47] are predicted as a range of FD∗L for the R2, S1, and U1 leptoquark models, respectively, where the current data of RD(∗) is satisfied at 1σ level. It is also shown that the τ polarization observables can much deviate from the SM predictions. The Belle II experiment, therefore, can check such correlations between RD(∗) and the polarization observables, and discriminate among the leptoquark models.