2 Search Results

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 $b\to c\tau \nu$ , i.e., $R_{J/\psi }$ , $R_{D_s}$ , $R_{D_s^{*}}$ , and $R_{{\mathrm{\Lambda }}_c}$ , where $\tau$ 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 $b\to c\tau \nu$ and the measurements of $b\to s{\tau }^{+}{\tau }^{-}$ and $b\to s\overline{\nu }\nu$ . We show that the limits on the LFU-violating energy scale can be pushed up to $\sim \mathcal{O}\left(10\right)\mathrm{TeV}$ for $\lesssim \mathcal{O}\left(1\right)$ Wilson coefficients at Tera- $Z$ . Published by the American Physical Society 2024

Novelty detection is a task of machine learning that aims at detecting novel events without a prior knowledge. In particular, its techniques can be applied to detect unexpected signals from new phenomena at colliders. In this paper, we develop an analysis scheme that exploits the complementarity, originally studied in ref. [1], between isolation-based and clustering-based novelty evaluators. This approach can significantly improve the performance and overall applicability of novelty detection at colliders, which we demonstrate using a variety of two dimensional Gaussian samples mimicking collider events. As a further proof of principle, we subsequently apply this scheme to the detection of two significantly different signals at the LHC featuring a $$t\bar{t}γγ$$ final state: $$t\bar{t}h$$, giving a narrow resonance in the diphoton mass spectrum, and gravity-mediated supersymmetry, resulting in broad distributions at high transverse momentum. Compared to existing dedicated searches at the LHC, the sensitivities for detecting both signals are found to be encouraging.