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$D^*$ polarization vs. $ {R}_{D^{\left(\ast \right)}} $ anomalies in the leptoquark models


Iguro, Syuhei; Kitahara, Teppei; Omura, Yuji; Watanabe, Ryoutaro; Yamamoto, Kei (2019). $D^*$ polarization vs. $ {R}_{D^{\left(\ast \right)}} $ anomalies in the leptoquark models. Journal of High Energy Physics, 2019(2):194.

Abstract

Polarization measurements in $\overline{B}\to {D}^{\left(\ast \right)}\tau \overline{\nu}$ are useful to check consistency in new physics explanations for the $R_D$ and $ {R}_{D^{\ast}} $ 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 ($F_L^{D*}$), which is recently measured by the Belle collaboration $F_{L}^{D*}$ = 0.60 ± 0.09, in model-independent manner and in each single leptoquark model (R2, S1 and U1) that can naturally explain the $ {R}_{D^{\left(\ast \right)}} $ anomalies. It is found that $ℬ(Bc^+ \to τ^+ν)$ severely restricts deviation from the Standard Model (SM) prediction of $F_{L,SM}$$^{D*}$ = 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 $F_L^{D*}$ for the R2, S1, and U1 leptoquark models, respectively, where the current data of $ {R}_{D^{\left(\ast \right)}} $ 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 $ {R}_{D^{\left(\ast \right)}} $ and the polarization observables, and discriminate among the leptoquark models.

Abstract

Polarization measurements in $\overline{B}\to {D}^{\left(\ast \right)}\tau \overline{\nu}$ are useful to check consistency in new physics explanations for the $R_D$ and $ {R}_{D^{\ast}} $ 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 ($F_L^{D*}$), which is recently measured by the Belle collaboration $F_{L}^{D*}$ = 0.60 ± 0.09, in model-independent manner and in each single leptoquark model (R2, S1 and U1) that can naturally explain the $ {R}_{D^{\left(\ast \right)}} $ anomalies. It is found that $ℬ(Bc^+ \to τ^+ν)$ severely restricts deviation from the Standard Model (SM) prediction of $F_{L,SM}$$^{D*}$ = 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 $F_L^{D*}$ for the R2, S1, and U1 leptoquark models, respectively, where the current data of $ {R}_{D^{\left(\ast \right)}} $ 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 $ {R}_{D^{\left(\ast \right)}} $ and the polarization observables, and discriminate among the leptoquark models.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Physical Sciences > Nuclear and High Energy Physics
Uncontrolled Keywords:Nuclear and High Energy Physics
Language:English
Date:1 February 2019
Deposited On:20 Aug 2019 12:31
Last Modified:03 Aug 2020 15:05
Publisher:Springer
ISSN:1029-8479
OA Status:Gold
Free access at:Publisher DOI. An embargo period may apply.
Publisher DOI:https://doi.org/10.1007/jhep02(2019)194

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