As one of the hypothetical principles in the Standard Model (SM), lepton flavor universality (LFU) should be tested with a precision as high as possible such that the physics violating this principle can be fully examined. The run of a factory at a future collider, such as the Circular Electron-Positron Collider or Future Circular Collider (electron/positron), provides a great opportunity to perform this task because of the large statistics and high reconstruction efficiencies for hadrons at the pole. In this paper, we present a systematic study on the LFU test in future factories. The goal is threefold. First, we study the sensitivities of measuring the LFU-violating observables of , i.e., , , , and , where decays muonically. For this purpose, we develop the strategies for event reconstruction, based on the track information significantly. Second, we explore the sensitivity robustness against detector performance and its potential improvement with the message of event shape or beyond the -hadron decays. A picture is drawn on the variation of analysis sensitivities with the detector tracking resolution and soft photon detectability, and the impact of Fox-Wolfram moments is studied on the measurement of relevant flavor events. Finally, we interpret the projected sensitivities in the SM effective field theory, by combining the LFU tests of and the measurements of and . We show that the limits on the LFU-violating energy scale can be pushed up to for Wilson coefficients at Tera- . Published by the American Physical Society 2024
@article{osti_2361181,
author = {Ho, Tin Seng Manfred and Jiang, Xu-Hui and Kwok, Tsz Hong and Li, Lingfeng and Liu, Tao},
title = {Testing lepton flavor universality at future <math display='inline'> <mrow> <mi>Z</mi> </mrow> </math> factories},
annote = { As one of the hypothetical principles in the Standard Model (SM), lepton flavor universality (LFU) should be tested with a precision as high as possible such that the physics violating this principle can be fully examined. The run of a Z factory at a future e + e − collider, such as the Circular Electron-Positron Collider or Future Circular Collider (electron/positron), provides a great opportunity to perform this task because of the large statistics and high reconstruction efficiencies for b hadrons at the Z pole. In this paper, we present a systematic study on the LFU test in future Z factories. The goal is threefold. First, we study the sensitivities of measuring the LFU-violating observables of b → c τ ν , i.e., R J / ψ , R D s , R D s * , and R Λ c , where τ decays muonically. For this purpose, we develop the strategies for event reconstruction, based on the track information significantly. Second, we explore the sensitivity robustness against detector performance and its potential improvement with the message of event shape or beyond the b -hadron decays. A picture is drawn on the variation of analysis sensitivities with the detector tracking resolution and soft photon detectability, and the impact of Fox-Wolfram moments is studied on the measurement of relevant flavor events. Finally, we interpret the projected sensitivities in the SM effective field theory, by combining the LFU tests of b → c τ ν and the measurements of b → s τ + τ − and b → s ν ¯ ν . We show that the limits on the LFU-violating energy scale can be pushed up to ∼ O ( 10 ) TeV for ≲ O ( 1 ) Wilson coefficients at Tera- Z . Published by the American Physical Society 2024 },
doi = {10.1103/PhysRevD.109.093004},
url = {https://www.osti.gov/biblio/2361181},
journal = {Physical Review. D.},
issn = {ISSN 2470-0010},
number = {9},
volume = {109},
place = {United States},
publisher = {American Physical Society},
year = {2024},
month = {05}}
Berger, Niklaus; Kozlinskiy, Alexandr; Kiehn, Moritz
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, Vol. 844https://doi.org/10.1016/j.nima.2016.11.012