# Analysis of Bc → τντ at CEPC

• The precise determination of the $B_c \to \tau\nu_\tau$ branching ratio provides an advantageous opportunity for understanding the electroweak structure of the Standard Model, measuring the CKM matrix element $|V_{cb}|$ and probing new physics models. In this paper, we discuss the potential of measuring the processes of $B_c \to \tau\nu_\tau$ with $\tau$ decaying leptonically at the proposed Circular Electron Positron Collider (CEPC). We conclude that during the Z pole operation, the channel signal can achieve five $\sigma$ significance with $\sim 10^9$ Z decays, and the signal strength accuracies for $B_c \to \tau\nu_\tau$ can reach around 1% level at the nominal CEPC Z pole statistics of one trillion Z decays assuming the total $B_c \to \tau \nu_\tau$ yield is $3.6 \times 10^6$. Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for the $b \to c\tau\nu$ transition. If the total $B_c$ yield can be determined to ${\cal{O}}$(1%) level of accuracy in the future, these results also imply $|V_{cb}|$ could be measured up to ${\cal{O}}$(1%) level of accuracy.
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Taifan Zheng, Ji Xu, Lu Cao, Dan Yu, Wei Wang, Soeren Prell, Yeuk-Kwan E. Cheung and Manqi Ruan. Analysis of Bcτντ at CEPC[J]. Chinese Physics C.
Taifan Zheng, Ji Xu, Lu Cao, Dan Yu, Wei Wang, Soeren Prell, Yeuk-Kwan E. Cheung and Manqi Ruan. Analysis of Bcτντ at CEPC[J]. Chinese Physics C.
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沈阳化工大学材料科学与工程学院 沈阳 110142

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## Analysis of Bc → τντ at CEPC

• 1. School of Physics, Nanjing University, Nanjing, China
• 2. INPAC, SKLPPC, MOE KLPPC, School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai, China
• 3. Physikalisches Institut der Rheinischen Friedrich-Wilhelms-Universität Bonn, 53115 Bonn, Germany
• 4. Institute of High Energy Physics, Beijing, China
• 5. Department of Physics and Astronomy, Iowa State University, Ames, IA, USA

Abstract: The precise determination of the $B_c \to \tau\nu_\tau$ branching ratio provides an advantageous opportunity for understanding the electroweak structure of the Standard Model, measuring the CKM matrix element $|V_{cb}|$ and probing new physics models. In this paper, we discuss the potential of measuring the processes of $B_c \to \tau\nu_\tau$ with $\tau$ decaying leptonically at the proposed Circular Electron Positron Collider (CEPC). We conclude that during the Z pole operation, the channel signal can achieve five $\sigma$ significance with $\sim 10^9$ Z decays, and the signal strength accuracies for $B_c \to \tau\nu_\tau$ can reach around 1% level at the nominal CEPC Z pole statistics of one trillion Z decays assuming the total $B_c \to \tau \nu_\tau$ yield is $3.6 \times 10^6$. Our theoretical analysis indicates the accuracy could provide a strong constraint on the general effective Hamiltonian for the $b \to c\tau\nu$ transition. If the total $B_c$ yield can be determined to ${\cal{O}}$(1%) level of accuracy in the future, these results also imply $|V_{cb}|$ could be measured up to ${\cal{O}}$(1%) level of accuracy.

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