arXiv subjects

Xin-Yang Li

Publications and source records attributed to Xin-Yang Li.

7 recordsLinked to original sources

arXiv2026

Probing the ALP--Photon--Dark Photon Interaction through the Mono-Photon plus Missing-Energy Signature at a Muon Collider

The dark axion portal provides a well-motivated framework for new physics beyond the Standard Model (SM), in which an axion-like particle (ALP) couples simultaneously to a photon and a dark photon, leading to distinctive collider signatures. In this work, we investigate the sensitivity to the $a$--$\gamma$--$\gamma'$ interaction via the mono-photon channel arising from $\mu^{+}\mu^{-} \to a \gamma'$ with $a \to \gamma \gamma'$ at the $1.5~\mathrm{TeV}$ muon collider with an integrated luminosity of $\mathcal{L}=500~\mathrm{fb}^{-1}$ for the polarized and unpolarized beam configurations, $P(\mu^+,\mu^-)=(-100\%,+100\%)$ and $P(\mu^+,\mu^-)=(0,0)$, using detector-level simulation. The signal is characterized by a single energetic photon accompanied by missing energy as the dark photons escape detection. The projected sensitivity reaches the $\mathcal{O}(10^{-5})~\mathrm{GeV}^{-1}$ level for ALP masses in the range $1~\mathrm{GeV}\leq m_a\leq1200~\mathrm{GeV}$ for $P(\mu^+,\mu^-)=(-100\%,+100\%)$, while for $P(\mu^+,\mu^-)=(0,0)$ the projected sensitivity reaches the $\mathcal{O}(10^{-4})~\mathrm{GeV}^{-1}$ level for the same ALP mass range. These results demonstrate that the mono-photon signature at a muon collider provides a sensitive probe of the $a$--$\gamma$--$\gamma'$ interaction over a wide mass range.

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arXiv2026

Prospects for probing neutral vector-like leptons via pair production at muon collider

Vector-like leptons (VLLs) are well-motivated candidates for physics beyond the Standard Model. We investigate the sensitivity of the $6$ TeV muon collider to the neutral doublet VLL (denoted as $N$) via its pair production within a general VLL framework. Taking vector-like muon as a case study, we study the subsequent decay $N\rightarrow W^+ μ$ and analyze two representative signals, namely $4j2μ$ and $2\ell2μE\mkern-10.5 mu/$, arising from the hadronic and leptonic decays of the $W$ boson, respectively. The signal and background events are simulated within a complete Monte Carlo framework, and a cut-based analysis is performed at the $6$ TeV muon collider with an integrated luminosity $\mathcal{L}=4$ ab$^{-1}$ and beam polarizations $(P_{μ^+},P_{μ^-})=(-1,1)$. We consider VLL masses in the range of $1300-3000$ GeV and evaluate the corresponding search sensitivity. Our results show that the future $6$ TeV muon collider can effectively probe neutral doublet VLLs through the $4j2μ$ and $2\ell2μE\mkern-10.5 mu/$ signals, with statistical significances exceeding $5σ$ over a broad mass range. These results demonstrate that the future $6$ TeV muon collider has excellent potential to search neutral doublet VLLs.

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arXiv2026

Prospects for probing light photophobic axion-like particles via displaced vertex signals at the CEPC

In recent years, long-lived particles (LLPs) have attracted increasing attention in searches for physics beyond the Standard Model (SM). In this paper, we investigate the discovery prospects for light, long-lived ALPs predicted by the photophobic ALP scenario through displaced-vertex signals at the CEPC, with a center-of-mass energy of $\sqrt{s}=91.2 $ GeV and an integrated luminosity of $\mathcal{L}=$ $100$ ab$^{-1}$. After comparing several possible single-production processes for the photophobic ALP, we focus on the dominant process $e^+ e^- \to Z \to a \gamma $, in which the ALP $a$ subsequently decays into a pair of charged leptons at a displaced vertex. Dedicated Monte Carlo simulations are performed for the $\mu^+ \mu^- \gamma$ and $\tau_h^+ \tau_h^- E\mkern-10.5 mu/_T \gamma$ signals. For the $\mu^+\mu^-\gamma$ signal, the CEPC is sensitive to the parameter region $g_{aWW} \in [1.27\times10^{-3},6.80\times10^{-1}]~\mathrm{TeV}^{-1}$ for $m_a \in [1,4]~\mathrm{GeV}$. For the $\tau_h^+\tau_h^- E\mkern-10.5 mu/_T \gamma$ signal, the accessible region is $g_{aWW} \in [7.00\times10^{-4},9.40\times10^{-3}]~\mathrm{TeV}^{-1}$ for $m_a \in [4,9]~\mathrm{GeV}$. These results demonstrate the substantial potential of the CEPC to explore light, long-lived ALPs through displaced-vertex signals, providing complementary coverage to existing searches at LEP and the LHC, as well as to the projected reach of the HL-LHC.

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arXiv2026

Searching for long-lived axion-like particles via displaced vertices at the HL-LHC

Axion-like particles (ALPs) are well-motivated extensions of the standard model (SM) that appear in numerous new physics scenarios. In this paper, we concentrate on searches for long-lived ALPs predicted by the photophobic scenario at the HL-LHC with the center-of-mass energy $\sqrt{s}=14$ TeV and the integrated luminosity $\mathcal{L}=$ $3$ ab$^{-1}$. We consider the process $pp \to γa$ with the ALP $a$ decaying into a pair of displaced charged leptons and perform a detailed analysis of two types of signals: $π^+ π^- γE\mkern-10.5 mu/_T $ and $\ell^+ \ell^- γE\mkern-10.5 mu/_T $. For the $π^+ π^- γE\mkern-10.5 mu/_T $ signal, we find that the prospective sensitivities of the HL-LHC can reach $g_{aWW}\in [8.72 \times 10^{-3}, 6.42 \times 10^{-2}]$ TeV$^{-1}$ for the ALP mass $m_a \in [4, 10]$ GeV. While for the $\ell^+ \ell^- γE\mkern-10.5 mu/_T $ signal, the HL-LHC can probe a broader parameter space, with the sensitivities covering $m_a \in [4, 10]$ GeV and $g_{aWW} \in [4.17 \times 10^{-3}, 2.00 \times 10^{-1}]$ TeV$^{-1}$. These long-lived searches complement some previous prompt decay studies from LEP and LHC experiments, extending the parameter space explored by the LHCb collaboration. Our results show that the HL-LHC has significant potential to probe long-lived ALPs via their displaced vertex signatures.

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arXiv2025

Probing the couplings of an axion-like particle with leptons via three-lepton final state processes at future $e^{-}p$ colliders

The axion-like particle (ALP) is one of the best motivated particles beyond the Standard Model (SM). We explore the possibility of detecting the couplings of ALP with leptons via three-lepton final state processes $e^- p \to e^- j a~(a \to \ell^+ \ell^-)$ at the LHeC (FCC-eh). For completeness, we investigate the cases where the ALP decays not only into electron and muon pairs but also into tau pairs, and perform a detailed simulation for the decays of taus. We find that the prospective sensitivities of the LHeC (FCC-eh) with the center-of-mass energy $\sqrt{s}=1.3~(3.5)$ TeV and the integrated luminosity $\mathcal{L}=1~ (2)$ ab$^{-1}$ to the ALP-lepton couplings are not only stronger than some existing bounds of the LHC and LEP but also complementary to the expected bounds of the CEPC and FCC-ee.

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arXiv2024

Single production of singlet vector-like leptons at the ILC

Vector-like leptons (VLLs) as one kind of interesting new particles can produce rich phenomenology at low- and high-energy experiments. In the framework of the singlet vector-like leptons with scalar (VLS) model, we investigate the discovery potential of VLL via its single production at the International Linear Collider (ILC) with the center of mass energy $\sqrt{s} =$ 1 TeV and the integrated luminosity $\mathcal{L}$ = 1 ab$^{-1}$, taking into account the appropriate polarization. For the signal and standard model (SM) background analysis, we have considered two kinds of decay channels for the W boson, i.e. pure leptonic and fully hadronic decay channels. Our analytic results show that the parameter space $M_{F}\in$ [300, 675] GeV and $κ\in$ [0.0294, 0.1] might be detected by the proposed ILC for pure leptonic decay channel. For fully hadronic decay channel, larger detection region of the parameter space are derived as $M_{F}\in$ [300, 700] GeV and $κ\in$ [0.0264, 0.0941].

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arXiv2024

Prospects for detecting the couplings of axion-like particle with neutrinos at the CEPC

We explore the possibility of detecting the couplings of axion-like particle (ALP) with leptons from their loop-level impact on the ALP couplings to electroweak (EW) gauge bosons via the signal process $e^+ e^- \to γγ{E\mkern-10.5 mu/}$ at the Circular Electron Positron Collider (CEPC) and obtain prospective sensitivities to the ALP-lepton couplings. Our numerical results show that the CEPC with the center of mass energy $\sqrt{s}=240~(91)$ GeV and the integrated luminosity $\mathcal{L}=5.6~(16)$ ab$^{-1}$ might be sensitive for probing the ALP-lepton couplings in the ALP mass range from $10$ GeV to $130~(50)$ GeV, where the prospective sensitivities to the ALP-neutrino coupling $Tr(g_{aνν})/f_a$ can be as low as $0.016~(0.012)$ GeV$^{-1}$ and $0.0031~(2.8 \times 10^{-4})$ GeV$^{-1}$ for $c_{R}=0$ and $c_{R}=c_{L}$, and to the ALP-charged lepton coupling $Tr(g_{a\ell\ell})/f_a$ can be as low as $0.035~(0.07)$ GeV$^{-1}$ for $c_{L}=0$. We find that the prospective sensitivities given by the CEPC are not covered by the current and expected exclusion regions in some ALP mass intervals. The CEPC has the potential for exploring the ALP-neutrino couplings via some promising processes induced by the ALP-EW gauge boson couplings in the future.

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