Jinmian Li

We present the first LHC search for quirks, particles with standard model and QCD-like infracolor (IC) interactions. The analysis uses data collected in 2022–2024 by FASER, with a 186 fb − 1 integrated luminosity of proton-proton collisions at a center-of-mass energy s = 13.6 TeV . Scintillator charge and timing information are used to search for slow pairs of quirks with no QCD color and electric charge ± 1 . No events are seen in this nearly background-free search, resulting in the first exclusion of quirks with masses above the weak scale for IC confinement scales in the broad range of 300 eV < Λ < 100 keV .

We investigate the atmospheric production and subsequent detection of sub-GeV dark mesons within the framework of a confining dark sector coupled to the Standard Model (SM) via a U ( 1 ) D vector portal. High-energy cosmic-ray interactions in the atmosphere produce dark quarks through proton bremsstrahlung, rare decays of Standard Model mesons, and Drell-Yan processes, which subsequently hadronize into dark mesons. We adopt a modified quark combination model to describe the nonperturbative dark hadronization process, allowing for a detailed event-level characterization of the dark meson flux. We simulate the flux and the interactions of these relativistic dark mesons in the Jiangmen Underground Neutrino Observatory (JUNO) using the generator, considering both elastic scattering off nuclei and deep inelastic scattering channels. Adopting a large-energy-singles-inspired conservative signal definition with 15 MeV < E vis < 100 MeV and vetoing events containing final-state neutrons, we derive projected 90% C.L. sensitivities to the coupling strength between the dark gauge boson and the SM sector for a 20 kton · year exposure. For the representative benchmark masses m Z ′ = 0.001 , 0.01, and 0.1 GeV, the projected JUNO reach corresponds to g SM 90 = 6.48 × 10 − 5 , 7.75 × 10 − 5 , and 2.37 × 10 − 4 , respectively. This reach is found to be only mildly sensitive to order-one variations of the hadronization parameter, as illustrated by the choices κ β = 1 / 3 , 1, and 3.

The dark photon is a well motivated candidate for the dark matter that comprises most of the mass of our visible Universe, leading to worldwide experimental and observational efforts toward its discovery. A primary tool in this search is the cavity haloscope, which facilitates resonantly enhanced conversion to photons from both dark photons and axions. In this context, limits from axion search experiments are often directly converted into dark photon constraints, without re-analyzing the original data. However, this rescaling may not fully capture all of the relevant physics due to various reasons. By reexamining data taken by the Taiwan Axion Search Experiment with Haloscope experiment, we derive a world-leading constraint on the dark photon parameter space, excluding | ε | ≳ 2 × 10 − 14 in the 19.46 – 19.84 μ eV mass range, which exceeds the naïve “rescaling limit” by roughly a factor of two. We emphasize that accounting for the scanning timing information is crucial for deriving limits for the polarized dark photon case. In the data, we also analyze a tentative signal excess with a local significance of 4.7 σ ( m X ≃ 19.5 μ eV ) that persists in the absence of a magnetic field. While this excess mimics the behavior of a dark photon signal, it has been excluded by recent results from the HAYSTAC and ORGAN-Q experiments. This case study, nevertheless, highlights the risk of discarding valid dark photon signals when relying on axion-specific magnetic field vetoes.

We introduce a novel end-to-end framework for jet reconstruction in high-energy collider events, leveraging the efficiency and long-range modeling capabilities of the Mamba architecture. Our model unifies instance segmentation, classification, and kinematic regression into a single multitask learning system, enabling a sophisticated multilevel reconstruction that simultaneously identifies primary heavy jets ( t , H , W / Z ) and their constituent subjets. To facilitate supervised learning for this complex task, we develop a novel method for assigning final-state hadrons to their ancestor colored partons using a mixed-integer linear programming solver, which generates high-fidelity ground-truth labels. The model achieves high classification accuracy, with an average precision score of 0.569 for W / Z -jets and 0.568 for b -jets, and shows exceptional precision in kinematic reconstruction. Furthermore, we show that the model not only maintains stable performance in high-pileup environments but also successfully reconstructs the mass peaks of beyond the standard model particles. This work presents a powerful and versatile new tool for comprehensive event reconstruction at the LHC.

We investigate TeV scale seesaw scenarios at μ + e − and μ + μ + colliders in the μ TRISTAN (Transposable Ring Intersecting STorage Accelerator in Nippon) experiment. In a minimal type I seesaw scenario, we consider two generations of Standard Model (SM) singlet heavy Majorana–type right-handed neutrinos, which couple with SM-gauge bosons through light-heavy neutrino mixing. We discuss the prospects of probing heavy neutrinos via the processes such as μ + e − → ν N i → e + j j ν or μ − j j ν for s = 346 GeV and 1 ab − 1 luminosity. Studying these process, we estimate limits on the light-heavy neutrino mixing angles as a function of heavy neutrino mass, which could be 2 orders of magnitude stronger than electroweak precision data. Further, we study the effect of a doubly charged scalar boson ( H + + ) from the type II seesaw scenario in μ + μ + collision at s = 2 TeV . In this case, we consider μ + μ + → ℓ i + ℓ j + and μ + μ + → H + + Z / γ processes followed by the same-sign dilepton decay of H + + . We find that events involving e + e + among these final states can probe the neutrino mass ordering in the μ TRISTAN experiment at 5 σ significance. In addition, we study the production of positively charged triplet fermions in μ TRISTAN following the μ + μ + → μ + Σ + process, where Σ + decays into μ + j j mode through Z boson exchange. Considering a triplet at 1 TeV and studying SM backgrounds, we estimate the discovery potential of the μ + μ + j j signal at μ TRISTAN with respect to projected luminosity.