Charged-Higgs on , polarization, and FBA

Chuan-Hung Chen; Takaaki Nomura

doi:10.1140/epjc/s10052-017-5198-6

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2023 Impact factor 4.2

Particles and Fields

Open Access

Eur. Phys. J. C (2017) 77: 631
https://doi.org/10.1140/epjc/s10052-017-5198-6

Regular Article - Theoretical Physics

Charged-Higgs on $R_{D^{(*)}}$ , $\tau$ polarization, and FBA

Chuan-Hung Chen¹ and Takaaki Nomura²^*

¹ Department of Physics, National Cheng-Kung University, Tainan, 70101, Taiwan
² School of Physics, KIAS, Seoul, 130-722, Korea

^* e-mail: nomura@kias.re.kr

Received: 1 June 2017
Accepted: 5 September 2017
Published online: 21 September 2017

Abstract

We study the influence of a charged-Higgs on the excess of branching fraction ratio, $R_M = BR(\bar{B} \rightarrow M \tau \bar{\nu }_\tau )/BR(\bar{B} \rightarrow M \ell \bar{\nu }_\ell )$ $$(M=D, D^*)$$ , in a generic two-Higgs-doublet model. In order to investigate the lepton polarization, the detailed decay amplitudes with lepton helicity are given. When the charged-Higgs is used to resolve excesses, it is found that two independent Yukawa couplings are needed to explain the $$R_D$$ and $R_{D^*}$ anomalies. We show that when the upper limit of $BR(B_c\rightarrow \tau \bar{\nu }_\tau )<30\%$ is included, $$R_D$$ can be significantly enhanced while $R_{D^*}<0.27$ . With the $BR(B_c\rightarrow \tau \bar{\nu }_\tau )$ constraint, we find that the $\tau$ -lepton polarizations can be still affected by the charged-Higgs effects, where the standard model (SM) predictions are obtained: $P^\tau _{D} \approx 0.324$ and $P^\tau _{D^*}\approx -0.500$ , and they can be enhanced to be $P^\tau _{D} \approx 0.5$ and $P^\tau _{D^*}\approx -0.41$ by the charged-Higgs. The integrated lepton forward–backward asymmetry (FBA) is also studied, where the SM result is $\bar{A}^{D^{(*)},\tau }_{FB}\approx -0.359(0.064)$ , and they can be enhanced (decreased) to be $\bar{A}^{D^{(*)},\tau }_{FB}\approx -0.33 (0.02)$ .