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Kingman Cheung

Publications and source records attributed to Kingman Cheung.

At least 37 records · Page 2Linked to original sources
arXiv2024

Comparison between $μ^{-}μ^{+}$ and $e^{-}e^{+}$ colliders for charged Higgs production in 2HDM

We study the phenomenology of the charged Higgs boson at future muon colliders. We investigate both the pair production $μ^+ μ^- \to H^+ H^-$, the single production $μ^+ μ^- \to W^\pm H^\mp$, as well as the Vector Boson Fusion (VBF) $\{e^+e^-, μ^+ μ^-\} \to ν\barν H^+ H^-$. We show that the neutral Higgs exchange diagrams in the muon collider case can lead to a significant boost in the cross sections through their Yukawa couplings. Our results for the muon collider are systematically compared to the corresponding ones at $e^+e^-$ machines. It is demonstrated that the vector boson fusion (VBF) $e^+e^- \to ν\barν H^+ H^-$ can compete with the mentioned $2\to 2$ processes. We select benchmark points and perform signal-background analyses, taking into account detector simulations. We demonstrate the discovery region at $5σ$ and the excluded region at $2σ$ levels at a 3 TeV muon collider.

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arXiv2024

Probing the Gauge-boson Couplings of Axion-like Particle at the LHC and High-Luminosity LHC

In this work, we calculate the sensitivities on the gauge-boson couplings $g_{aZZ}$, $g_{aZγ}$, and $g_{aWW}$ of an axion-like particle (ALP) that one can achieve at the LHC with $\sqrt{s}=14$ TeV and integrated luminosities of 300 fb$^{-1}$ (current run) and 3000 fb$^{-1}$ (High-Luminosity LHC). We focus on the associated production processes $pp\to Za \to (l^+l^-)(γγ)$ and $pp\to W^\pm a \to (l^\pm ν)(γγ)$. We show that better sensitivities on these gauge couplings can be achieved at the LHC for $M_a = 1-100$ GeV, down to the level of $10^{-4}\,{\rm GeV}^{-1}$. In conclusion, this study emphasizes the significance of the investigated channels in constraining the ALP couplings at the LHC, offering valuable insights for future experiments dedicated to ALP detection.

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arXiv2024

Probing dark photons from a light scalar at Belle II

In the minimal $U(1)$ extension of the Standard Model (SM), a new gauge boson referred to as "dark photon" is predicted. The dark-photon mass can be generated from an additional Higgs mechanism associated with a dark scalar boson. At $B$-factories such as Belle II, large numbers of $B$-mesons are produced and can decay to a kaon plus the dark scalar via the latter's mixing with the SM Higgs boson. We evaluate the sensitivity of Belle II for the case in which the dark scalar decays exclusively into a pair of dark photons via the new $U(1)$ gauge coupling, and the dark photons are long lived owing to a small kinetic mixing $ε$. We study the experimental signature in which each dark photon decays into a pair of charged leptons, pions, or kaons, resulting in a pair of displaced vertices, and argue that the search is essentially background-free. We perform detailed Monte-Carlo simulations to determine the expected number of signal events at Belle II with an integrated luminosity of 50 ab$^{-1}$, taking into account the efficiencies for both final-state-particle identification and displaced tracking. We find that for experimentally allowed values of the scalar mixing angle and kinematically allowed dark-photon and dark-scalar masses, the proposed search is uniquely sensitive to the medium-$ε$ regime, which is currently mostly unexcluded by experiments.

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arXiv2023

Leptoquark search at the Forward Physics Facility

In this study, we calculate the sensitivity reach on the vector leptoquark (LQ) $U_1$ at the experiments proposed in Forward Physics Facility (FPF), including FASER$ν$, FASER$\nu2$, FLArE (10 tons), and FLArE (100 tons) using the neutrino-nucleon scattering ($νN \rightarrow νN'$ and $νN \rightarrow l N'$). We cover a wide mass range of $10^{-3}$ GeV $\leq M_{LQ}\leq 10^4$ GeV. The new result shows that the FLArE (100 tons) offers the best sensitivity to the LQ model. The sensitivity curves for all the experiments follow a similar pattern with weakened sensitivities with the increment of the LQ mass. We combine the sensitivities obtained from the neutral- and charged-current interactions of the neutrinos.

hep-ph↗
arXiv2023

NANOGrav Signal and PBH from the Modified Higgs Inflation

This study investigates the classical Higgs inflation model with a modified Higgs potential featuring a dip. We examine the implications of this modification on the generation of curvature perturbations, stochastic gravitational wave production, and the potential formation of primordial black holes (PBHs). Unlike the classical model, the modified potential allows for enhanced power spectra and the existence of PBHs within a wide mass range $1.5\times10^{20}$ g -- $9.72\times10^{32}$ g. We identify parameter space regions that align with inflationary constraints and have the potential to contribute significantly to the observed dark matter content. Additionally, the study explores the consistency of the obtained parameter space with cosmological constraints and discusses the implications for explaining the observed excess in gravitational wave signals, particularly in the NANOGrav experiment. Overall, this investigation highlights the relevance of the modified Higgs potential in the classical Higgs inflation model, shedding light on the formation of PBHs, the nature of dark matter, and the connection to gravitational wave observations.

hep-ph↗
arXiv2023

Axion Like Particle Search at Higgs Factories

We study the potential of the future Higgs factories, including the ILC, CEPC, and FCC-ee with $\sqrt{s}$ = 240-250 GeV on discovering axion-like particles (ALPs) through various production channels in the leptonic final states, $e^+e^- \to f\bar{f} a$, where $f=e,μ,ν$. We show that the $e^+e^- \to e^+e^- a$ with $a \to γγ$ provides the best bounds for the $g_{aγγ}$ and $g_{aZZ}$ couplings, while $e^+e^- \to ν\barνa$, with $a \to γγ$ offers the best bounds for the $g_{aZZ}$ and $g_{aZγ}$ couplings. The $e^+e^- \to μ^+μ^- a$ with $ a \to γγ$ provides intermediate sensitivity to the $g_{aZZ}$ coupling. Our estimates of the bounds for the $g_{aγγ}$, $g_{aZγ}$, and $g_{aZZ}$ couplings as a function of ALP mass ($M_a$) ranging from 0.1 GeV to 100 GeV provide valuable insights for future experiments aiming to detect ALPs. We find that $g_{aγγ}$ around $1.5\times10^{-4}~\rm GeV^{-1}$ for $M_a = 0.1-6$ GeV is currently not ruled out by any other experiments.

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arXiv2022

Atmospheric axion-like particles at Super-Kamiokande

We consider a muonphilic axion-like-particle (ALP), denoted as $a$, lighter than twice the muon mass. ALPs of this mass range dominantly decay into a pair of photons, induced by a triangular muon loop. Such light muonphilic ALPs are naturally long-lived. At the atmosphere, the ALPs are copiously produced from charged-meson decays in air showers, such as $π^\pm \to μ^\pm νa$, via the ALP-muon coupling $g_{aμμ}$. After propagating tens of kilometers, the ALPs decay with $a\to γγ$ inside large-volume Cherenkov detectors near the Earth's surface, such as Super-Kamiokande (SK). We find the present SK observation constrains on muonphilic ALPs of mass range [1 MeV, 30 MeV] and ALP-muon coupling $[10^{-3}$, $10^{2}]$, assuming the proper decay length $cτ_a$ in [$10^{-3}$ km, $10^6$ km] either dependent on or independent of $g_{aμμ}$. We conclude that atmospheric searches of such exotic states can be complementary to collider and beam-dump experiments as well as astrophysical probes.

hep-ph↗
arXiv2022

The Role of a Heavy Neutrino in the Gamma-Ray Burst GRB-221009A

Recently, several telescopes, including Swift-BAT, GBM, and LHAASO, have observed the ever highest-energy and long-duration gamma-rays from a gamma-ray burst named as GRB221009A (located at a red-shift of $z=0.151$) on October 9, 2022. Conventional understanding tells us that very high-energy photons produced at such a far distance suffer severe attenuation before reaching the Earth. We propose the existence of a sub-MeV to $O(10)$ MeV heavy neutrino with a transitional magnetic dipole moment, via which the heavy neutrino is produced at the GRB. It then travels a long distance to our galaxy and decays into a neutrino and a photon, which is observed. In such a way, the original high-energy photon produced at the GRB can survive long-distance attenuation.

hep-ph↗
arXiv2022

Sensitivities on dark photon from the Forward Physics Experiments

Neutrino-electron scattering experiments can explore the potential presence of a light gauge boson $A'$ which arises from an additional $U(1)_{B-L}$ group, or a dark photon $A'$ which arises from a dark sector and has kinetic mixing with the SM hypercharge gauge field. We generically call it a dark photon. In this study, we investigate the effect of the dark photon on neutrino-electron scattering $νe^-\rightarrowνe^-$ at the newly proposed forward physics experiments such as FASER$ν$, FASER$\nu2$, SND@LHC and FLArE(10 tons). We estimate the anticipated sensitivities to the $U(1)_{B-L}$ gauge coupling in a wide range of the dark photon mass $M_{A'}$. We compare the sensitivities of the proposed forward physics experiments with the current limits from TEXONO, GEMMA, BOREXINO, LSND, and CHARM II as well as NA64e experiments. We also extend the calculation to obtain the sensitivities on the kinetic mixing parameter $ε$ in a wide range of dark photon mass $M_{A'}$. We demonstrate that the sensitivities do not improve for $M_{A'} < 1 $ GeV at the Forward Physics Facilities.

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arXiv2022

Sensitivity on Two-Higgs-Doublet Models from Higgs-Pair Production via $b\bar{b}b\bar{b}$ Final State

Higgs boson pair production is well known to probe the structure of the electroweak symmetry breaking sector. We illustrate using the gluon-fusion process $pp \to H \to h h \to (b\bar b) (b\bar b)$ in the framework of two-Higgs-doublet models and how the machine learning approach (three-stream convolutional neural network) can substantially improve the signal-background discrimination and thus improves the sensitivity coverage of the relevant parameter space. We show that such $gg \to hh \to b \bar b b\bar b$ process can further probe the currently allowed parameter space by HiggsSignals and HiggsBounds at the HL-LHC. The results for Types I to IV are shown.

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arXiv2022

Status of the two-Higgs-doublet model in light of the CDF $m_W$ measurement

The most recent $W$-boson mass measurement by the CDF collaboration with a substantially reduced uncertainty indicates a significant deviation from the standard model prediction, as large as $7σ$ if taken literally. Then the Peskin-Takeuchi parameters of $S$ and $T$ shift to larger values, which has profound consequences in searching for physics beyond the SM. In the framework of two-Higgs-doublet models, we study the effect of the new $W$-boson mass measurement on the parameter space. Combined with other constraints including theoretical requirements, flavor-changing neutral currents in $B$ physics, the cutoff scale above 1 TeV, Higgs precision data, and direct collider search limits from the LEP, Tevatron, and LHC experiments, we find upper bounds on the masses of the heavy Higgs bosons: $M_{H, A, H^\pm} \lesssim 1.1$ TeV in type I, II, X, and Y for the normal Higgs scenario; $M_{H^\pm} \lesssim 450 $ GeV and $M_{A} \lesssim 420 $ GeV in type I and X for the inverted scenario where the heavier $CP$-even Higgs boson is the observed one. Another important finding is that type II and type Y in the inverted scenario are completely excluded. Such unprecedented findings imply that the upcoming LHC run can readily close out a large portion of the still-available parameter space.

hep-ph↗
arXiv2022

Constraining the Active-to-Heavy-Neutrino transitional magnetic moments associated with the $Z'$ interactions at FASER$ν$

We investigate the effects of the transitional magnetic dipole moment of the active-to-heavy-neutrino associated with a new neutral gauge boson $Z'$ on neutrino-nucleon scattering at the ForwArd Search ExpeRiment-$ν$ (FASER$ν$). We consider the neutral-current neutrino-nucleon scattering ($νA\rightarrow N A$) as the production mechanism of the heavy neutrino $N$ at FASER$ν$ and estimate the sensitivity reach on the magnetic moment coupling $μ_{ν_α}$ for a range of heavy neutrino mass ($1\,{\rm GeV} < M_{N} < 70 {\rm GeV}$). In this study, we consider three benchmark models, in which the heavy neutrino is coupled to $L_e$, $L_μ$ or $L_τ$ doublet, respectively.

hep-ph↗
arXiv2022

Comprehensive study of the light charged Higgs boson in the type-I two-Higgs-doublet model

In the type-I two-Higgs-doublet model, existing theoretical and experimental constraints still permit the light charged Higgs boson with a mass below the top quark mass. We present a complete roadmap for the light charged Higgs boson at the LHC through the comprehensive phenomenology study, focusing on the normal scenario where the lighter \textit{CP}-even Higgs boson is the observed Higgs boson. In type-I, it is challenging to simultaneously accommodate the light mass of the charged Higgs boson and the constraints from theory, electroweak precision data, Higgs data, $b\to s γ$, and direct search bounds. Consequently, the parameter space is extremely curtailed, which predicts somewhat definite phenomenological signatures. We find that the mass of the pseudoscalar Higgs boson, $M_A$, is the most crucial factor in the phenomenology of the charged Higgs boson. If $M_A$ is light, the charged Higgs boson decays mainly into $A W^\pm$. When $M_A$ is above the $A W^\pm$ threshold, the dominant decay mode is into $ τ^\pm ν$. Over the whole viable parameter space, we study all the possible production and decay modes of charged Higgs bosons at the LHC, and suggest three efficient channels: (i) $pp \to H^+ H^-\to [τν] [τν]$; (ii) $pp \to HA/HH/AA \to H^\pm W^\mp H^\pm W^\mp \to [τν] [τν] W W$; (iii) $pp \to H^+ H^-\to [b \bar b W ] [b \bar b W ] $. Based on the sophisticated signal-background analyses including detector simulation, we showed that the significance of the first final state is large, that of the second one is marginal around three, but the third one suffers from huge $t\bar t$ related backgrounds.

hep-ph↗
arXiv2022

Exploring the Universality of Hadronic Jet Classification

The modeling of jet substructure significantly differs between Parton Shower Monte Carlo (PSMC) programs. Despite this, we observe that machine learning classifiers trained on different PSMCs learn nearly the same function. This means that when these classifiers are applied to the same PSMC for testing, they result in nearly the same performance. This classifier universality indicates that a machine learning model trained on one simulation and tested on another simulation (or data) will likely be optimal. Our observations are based on detailed studies of shallow and deep neural networks applied to simulated Lorentz boosted Higgs jet tagging at the LHC.

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arXiv2022

Inverting cosmic ray propagation by Convolutional Neural Networks

We propose a machine learning method to investigate the propagation of cosmic rays based on the precisely measured spectra of the primary and secondary cosmic ray nuclei of Li, Be, B, C, and O from AMS-02, ACE, and Voyager-1. We train two convolutional neural networks. One network learns how to infer propagation and source parameters from the energy spectra of cosmic rays, and the other network, which is similar to the former, has the flexibility to learn from the data with added artificial fluctuations. Together with the simulated data generated by GALPROP, we find that both networks can properly invert the propagation process and infer the propagation and source parameters reasonably well. This approach can be much more efficient than the traditional Markov chain Monte Carlo fitting method for deriving the propagation parameters if users choose to update confidence intervals with new experimental data. Both of the trained networks are available at (https://github.com/alan200276/CR_ML).

astro-ph.HE↗
arXiv2021

Probing charged lepton flavor violation with axion-like particles at Belle II

We study charged lepton flavor violation associated with a light leptophilic axion-like particle (ALP), $X$, at the $B$-factory experiment Belle II. We focus on production of the ALP in the tau decays $τ\to X l$ with $l=e,μ$, followed by its decay via $X\to l^- l^+$. The ALP can be either promptly decaying or long-lived. We perform Monte-Carlo simulations, recasting a prompt search at Belle for lepton-flavor-violating $τ$ decays, and propose a displaced-vertex (DV) search. For both types of searches, we derive the Belle~II sensitivity reaches in both the product of branching fractions and the ALP coupling constants, as functions of the ALP mass and lifetime. The results show that the DV search exceeds the sensitivity reach of the prompt search to the relevant branching fractions by up to about a factor of 40 in the long decay length regime.

hep-ph↗
arXiv2021

Time-delayed electrons from neutral currents at the LHC

We investigate long-lived particles (LLPs) produced in pair from neutral currents and decaying into a displaced electron plus two jets at the LHC, utilizing the proposed minimum ionizing particle timing detector at CMS. We study two benchmark models: the R-parity-violating supersymmetry with the lightest neutralinos being the lightest supersymmetric particle and two different $U(1)$ extensions of the standard model with heavy neutral leptons (HNLs). The light neutralinos are produced from the standard model $Z$-boson decays via small Higgsino components, and the HNLs arise from decays of a heavy gauge boson, $Z'$. By simulating the signal processes at the HL-LHC with the center-of-mass energy $\sqrt{s}=$ 14 TeV and integrated luminosity of 3 ab$^{-1}$, our analyses indicate that the search strategy based on a timing trigger and the final state kinematics has the potential to probe the parameter space that is complementary to other traditional LLP search strategies such as those based on the displaced vertex.

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