arXiv subjects

Yao-Bei Liu

Publications and source records attributed to Yao-Bei Liu.

At least 19 recordsLinked to original sources

arXiv2026

Searching for vectorlike $T$ quarks in the $T\to tZ$ channel at a future muon-proton collider

We investigate the discovery potential of a singly produced vector-like top quark $T$ in the $T\to tZ$ decay channel at future muon-proton ($μp$) colliders, considering three benchmark center-of-mass energies: $\sqrt{s}=5.29$, $6.48$, and $9.16$~TeV. The baseline signal final state consists of a semileptonic top decay $t\to bW\to b\ellν$ and a hadronic $Z\to q\bar{q}$ decay, where the collimated quark pair from the $Z$ boson is reconstructed as a single large-radius fat jet $J$. Full detector-level Monte Carlo simulations are performed for both the signal process and the dominant Standard Model backgrounds. We derive the $5σ$ discovery contours and the $95\%$ confidence level exclusion limits in the two-dimensional parameter space spanned by the VLQ mass $m_T$ and the effective coupling $g^*$. A comparison with the $T\to Wb$ channel and with searches at other collider facilities reveals that the $T\to tZ$ decay mode provides complementary sensitivity and offers unique advantages for probing high-mass vector-like $T$ quarks in the boosted jet topology.

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arXiv2026

Probing the Single Production of First-Generation Singlet Vector-like Leptons at Future $e^+e^-$ Colliders

We study the single production of first-generation weak-isosinglet vector-like leptons (VLLs) at future $e^+e^-$ colliders, considering the channels $e^+e^- \to e^{\pm}E^{\mp}$ with $E^{\pm} \to W^{\pm}ν_e$ and $E^{\pm} \to e^{\pm}Z$. For the heavy VLL masses under consideration, the decay products of the highly boosted $W$ and $Z$ bosons merge into a single fat-jet, providing a powerful handle for signal identification and background suppression. A comprehensive Monte Carlo simulation is carried out at $\sqrt{s}=1$ TeV at the International Linear Collider (ILC) and 1.5 TeV at the Compact Linear Collider (CLIC). The $2σ$ exclusion and $5σ$ discovery reaches are determined as functions of the integrated luminosity and the mixing parameter $\sinθ_L$ for representative benchmark masses. Our results show that future $e^+e^-$ colliders can effectively probe the first-generation singlet VLL scenario through these channels. The 1 TeV ILC can probe masses up to 900 GeV, while the 1.5 TeV CLIC extends the reach to 1400 GeV, surpassing existing limits from hadron colliders and complementing constraints from electroweak precision measurements.

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arXiv2026

Search for heavy Majorana neutrinos at muon-proton colliders via lepton-number-violating signals

We propose a novel search strategy for heavy Majorana neutrinos based on the lepton-number-violating process $μ^{-}p \to jN \to j(\ell^{+}W^{-})$ at future muon-proton ($μp$) colliders equipped with 1 TeV muon beams and 7 TeV proton beams, yielding a center-of-mass energy of approximately 5.3 TeV. For heavy neutrinos with masses in the range $200~\text{GeV} \lesssim m_N \lesssim 1000~\text{GeV}$, this analysis targets the decay chain $N \to \ell^{+}W^{-} \to \ell^{+}jj$, producing a characteristic final state consisting of one charged lepton and three well-resolved jets. For TeV-scale Majorana neutrinos, the $W$ boson is highly boosted, such that its hadronic decay products coalesce into a prominent fat-jet ($J$) signature. We conduct comprehensive signal and background analyses that account for realistic detector effects to assess the search sensitivity. We derive the projected $2σ$ exclusion limits on the neutrino mixing parameter $|V_{\ell N}|^2$ based on two typical integrated luminosity scenarios of $100~\text{fb}^{-1}$ and $1~\text{ab}^{-1}$. The results demonstrate that the proposed search strategy can achieve constraints substantially superior to the existing bounds from the LHC and other high-energy colliders. This study demonstrates that future $μp$ colliders can provide competitive sensitivity for probing heavy Majorana neutrinos over the mass range $200~\text{GeV} \leq m_N \leq 3000~\text{GeV}$.

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arXiv2026

Scalar Resonances near 650 and 95 GeV in the GNMSSM with Correct Dark Matter Relic Abundance

Recent CMS analyses report an excess in the diphoton-plus-$b \bar{b}$ channel, indicative of a heavy resonance around 650 GeV decaying into a Standard Model (SM)-like Higgs boson and a lighter scalar near 95 GeV. The case for a 95 GeV state is further supported by diphoton excesses observed by both CMS and ATLAS, as well as a $b\bar{b}$ excess previously observed at the Large Electron-Position collider. This study presents a unified interpretation of these anomalies within the framework of the General Next-to-Minimal Supersymmetric Standard Model that naturally accommodates a light singlet-dominated $CP$-even scalar boson $h_s$ near 95 GeV and a heavier doublet-like scalar boson $A_H$ near 650 GeV. Through a comprehensive scan of the parameter space, we demonstrate that the model can explain these excesses at $2\,σ$ level while satisfying constraints from the dark matter relic density, direct detection experiments, the properties of the 125 GeV Higgs boson, $B$-physics observables, and searches for electroweakinos at the Large Hadron Collider (LHC). The interpretation features a Bino-dominated lightest neutralino as the dark matter candidate, whose relic abundance is achieved primarily via $A_s$ funnel annihilation or coannihilation with $\tilde{S}$-like $\tildeχ^0_2$s into $h_sA_H$ final states. Our findings provide clear predictions for testing this scenario at the high-luminosity LHC and future colliders.

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arXiv2026

Probing the pair production of first-generation vector-like leptons at future $e^+e^-$ colliders

This work explores the discovery potential of the first-generation weak isosinglet Vector-Like Leptons (VLLs), denoted by $E^\pm$, via pair production at future electron-positron colliders. Our analysis adopts a comprehensive framework that incorporates beam polarization configurations and leverages detailed detector simulations. We focus on two distinct multilepton signatures: the $2\ell + 2j + \slashed{E}_T$ and $3\ell + 2j + \slashed{E}_T$ final states ($\ell = e, μ$). Both signatures arise from the decay $E^{\pm} \to Z e^{\pm} / W^{\pm} ν_\ell$ and are distinguished by the decay patterns of the associated gauge bosons. By applying optimized selection criteria to both signal and background events, we establish exclusion sensitivities and discovery prospects across the VLL mass spectrum. Our findings demonstrate that, for integrated luminosities of $\SI{25}{fb^{-1}}$, $\SI{90}{fb^{-1}}$ and $\SI{1000}{fb^{-1}}$ at corresponding center-of-mass (c.m.) energies of $\SI{1}{TeV}$, $\SI{1.5}{TeV}$ and $\SI{3}{TeV}$, the accessible mass range extends to approximately $\SI{490}{GeV}$, $\SI{740}{GeV}$ and $\SI{1440}{GeV}$, which represents a substantially improvement over the detection limits of existing hadron collider experiments.

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arXiv2026

Searches for heavy neutrinos at a 3 TeV CLIC in fat jet final states

Heavy Majorana neutrinos ($N$) are predicted in many models of physics beyond the Standard Model. In this work, we explore the production and detection prospects of TeV-scale heavy neutrinos ($m_N \gtrsim 1$ TeV) at a future 3 TeV Compact Linear Collider (CLIC). We focus on two distinct decay topologies: (i) $N \to \ell^{\pm} W^{\mp}$ with hadronic $W$ boson decay, leading to a final state with one charged lepton and a hadronic fat-jet $J_W$; and (ii) $N \to νh$ with subsequent Higgs decay $h \to b\bar{b}$, yielding a Higgs-tagged fat-jet $J_h$ and $\slashed{E}_T$. Based on comprehensive detector-level simulations and background analysis, we present both $2σ$ exclusion limits and $5σ$ discovery reaches in the $m_N$-$|V_{\ell N}|^2$ plane. We further extract 95\% confidence level upper limits on the mixing parameter $|V_{\ell N}|^2$, and perform a detailed comparison with existing constraints from direct searches at future colliders and indirect global fits. Our findings demonstrate that a 3 TeV CLIC can improve the sensitivity to $|V_{\ell N}|^2$ by about two orders of magnitude compared to the projected reaches of future hadron colliders, while remaining competitive with other CLIC search channels.

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arXiv2025

Searching for single production of vectorlike quarks decaying into Wb at a future muon-proton collider

This work investigates the discovery potential for singly produced vectorlike quarks~(VLQs) $T$ ($Q=+2/3e$) and $Y$ ($Q=-4/3e$) decaying to $Wb$ at future $μp$ colliders with $\sqrt{s}=5.29$, 6.48, and 9.16 TeV, analyzing both leptonic and hadronic $W$ decay channels through detailed detector simulations. The hadronic channel demonstrates superior sensitivity, enabling $5σ$ discovery up to $m_T=3750$ GeV ($m_Y=4100$ GeV) at 9.16 TeV with 100 fb$^{-1}$, while exclusion limits reach $m_T=4500$ GeV ($g^*\geq0.06$) and $m_Y=4800$ GeV ($κ_Y\geq0.04$) - significantly beyond LHC capabilities. At 5.29 TeV, discovery regions cover $g^*\in[0.15,0.5]$ for $m_T\in[1500,2520]$ GeV and $κ_Y\in[0.12,0.5]$ for $m_Y\in[1700,2700]$ GeV, with exclusions extending to $m_T=2750$ GeV and $m_Y=3020$ GeV. These results, obtained within a simplified two-parameter framework ($m_{T/Y}$ and electroweak couplings $g^{\ast}$), establish $μp$ colliders as uniquely powerful tools for probing high-mass VLQ states, particularly in the boosted jet regime.

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arXiv2024

Single production of vectorlike quarks with charge 5/3 at the 14 TeV LHC

Vectorlike quarks have been predicted in many new physics scenarios beyond the Standard Model (SM), which can have sizable couplings to first generation quarks without conflicting with current experimental constraints. In a framework of the SM simply extended by an SU(2) doublet $\left(X,T\right)$ including a vectorlike quark $X$~(VLQ-$X$), with electric charge $|Q_{X}| = 5/3$, we investigate the single production of the VLQ-$X$ induced by the couplings between the VLQ-$X$ with the first and the third generation quarks at the Large Hadron Collider (LHC) Run-III and High-Luminosity LHC (HL-LHC) operating at $\sqrt{s}=14$~TeV. The signal is searched in events including same-sign dileptons (electrons or muons), one $b$-tagged jet and missing energy, where the X quark is assumed to decay into a top quark and a W boson, both decaying leptonically. After a rapid simulation of signal and background events, the 95\% CL exclusion limits and the $5σ$ discovery reach are respectively obtained at the 14 TeV LHC with an integrated luminosity of 300 and 3000 fb$^{-1}$, respectively.

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arXiv2024

Pair production of the singlet vector-like B quark at the CLIC

Vector-like quarks~(VLQs) are a common feature of many scenarios of new physics beyond the Standard Model~(SM), which generally decay into a SM third-generation quark with a SM gauge boson, or a Higgs boson. The presence of a new exotic decay mode of VLQs will reduce the branching ratios of these standard decay modes and thus relax the current mass exclusion limits from LHC experiments. Based on a model-independent framework, we investigate the prospect of discovering the pair production of the weak-singlet VLQ-$B$ at the future 3-TeV Compact Linear Collider~(CLIC), by focusing on the final states including one $Z$ boson and four $b$-jets via two types of modes: $Z\to \ell^{+}\ell^{-}$ and $Z\to ν\barν$. By performing a rapid detector simulation of the signal and background events, and considering the initial state radiation and beamstrahlung effects, the exclusion limit at the 95\% confidence level and the $5σ$ discovery prospects are respectively obtained on the branching ratio of $B\to bZ$ and the VLQ-$B$ masses at the future 3-TeV CLIC with an integrated luminosity of 5 ab$^{-1}$.

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arXiv2022

Search for pair production of the heavy vectorlike top partner in same-sign dilepton signature at the HL-LHC

New vectorlike quarks are predicted in many new physics scenarios beyond the Standard Model~(SM) and could potentially be discovered at the LHC. Based on a simplified model including a singlet vectorlike top partner with charge $2/3$, we investigate the process $pp \to TT$ via a $t$-channel induced by the couplings between the top partner with the first-generation SM quarks. We calculate the production cross section and further study the observability of the heavy top partner in the channel $T\to Wq$ at the high-luminosity LHC (HL-LHC) using final states with same-sign dileptons (electrons or muons), two jets, and missing transverse momentum. At the 14 TeV LHC with an integrated luminosity of 3000 fb$^{-1}$, the $2σ$ exclusion limits, as well as the $5σ$ discovery reach in the parameter plane of the two variables $g^{\ast}-R_L$, are respectively obtained at the HL-LHC. We also obtain the $2σ$ exclusion limit on the coupling strength parameter $g^{\ast}$ in the case in which the vectorlike top partner is coupled only to the first-generation quarks.

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arXiv2022

Search for single production of vectorlike $B$-quarks at the LHC

New vectorlike quarks have been proposed in many scenarios of new physics beyond the Standard Model, which address the hierarchy problem and may be potentially discovered at the Large Hadron Collider~(LHC). Based on a model-independent framework, we propose to search for the vectorlike $B$-quark~(VLQ-$B$) and focus on resonant production via $b$-gluon fusion through chromomagnetic interactions. We then explore the possible signals of the VLQ-$B$ through the $B\to tW$ decay mode at the 14 TeV LHC. After a rapid simulation of signal and background events, the $2σ$ excluded regions and the $5σ$ discovery reach in the parameter plane of $κ_{B}-M_B$ are obtained at the LHC with an integrated luminosity of 300~(3000) fb$^{-1}$ in the dilepton final states.

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arXiv2022

Single production of vector-like $T$ quark at future high-energy linear $e^{+}e^{-}$ collider

Based on a model-independent framework including the vector-like top partner (VLQ-$T$), we investigate the prospect of discovering the singlet or doublet VLQ-$T$ via the single production process $e^{-}e^{+}\to T\bar{t}+t\bar{T}$ with the $T\to Zt$ decay channel at future high energy linear $e^{+}e^{-}$ collider with $\sqrt{s}=3$ TeV. We focus on the hadronic decay of the top quark and two types of decay channel for the $Z$ boson: $Z\to \ell^{+}\ell^{-}$ and $Z\to ν\barν$. By carrying out a full simulation for the signals and the relevant SM backgrounds, the $2σ$ exclusion limit and $5σ$ discovery prospects are, respectively, obtained on the VLQ-$T$ mass and the coupling strength $g^{\ast}$ with the integrated luminosity of 5 ab$^{-1}$. In addition, we considered the initial state radiation and beamstrahlung effects as well as the systematic uncertainty effects of backgrounds, which are found to reduce the excluding or discovery capability.

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arXiv2021

Probing tqZ anomalous couplings in the trilepton signal at the HL-LHC, HE-LHC and FCC-hh

We investigate the prospects for discovering the Flavour Changing Neutral Current (FCNC) $tqZ$ couplings via two production processes yielding trilepton signals: top quark pair production $pp\to t\bar{t}$ with one top decaying to the $Z$ boson and one light jet and the anomalous single top plus $Z$ boson production process $pp\to tZ$. We study these channels at various successors of the Large Hadron Collider~(LHC), i.e., the approved High-Luminosity LHC (HL-LHC) as well as the proposed High-Energy LHC~(HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh). We perform a full simulation for the signals and the relevant Standard Model (SM) backgrounds and obtain limits on the Branching Ratios (BRs) of $t\to qZ~(q=u,c)$, eventually yielding a trilepton final state through the decay modes $t\to b W^{+}\to b\ell^{+}ν_{\ell}$ and $Z\to \ell^{+}\ell^{-}$. The upper limits on these FCNC BRs at 95\% Confidence Level (CL) are obtained at the HL-LHC with $\sqrt s=14$ TeV and 3 ab$^{-1}$, at the HE-LHC with $\sqrt s=27$ TeV and 15 ab$^{-1}$ as well as at the FCC-hh with $\sqrt s=100$ TeV and 30 ab$^{-1}$.

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arXiv2020

Signatures of vector-like top partners decaying into new neutral scalar or pseudoscalar bosons

We explore the phenomenology of models containing one Vector-Like Quark (VLQ), $t'$, which can decay into the Standard Model (SM) top quark, $t$, and a new spin-0 neutral boson, $S$, the latter being either a scalar or pseudoscalar state. We parametrise the underlying interactions in terms of a simplified model which enables us to capture possible Beyond the SM (BSM) scenarios. We discuss in particular three such scenarios: one where the SM state is supplemented by an additional scalar, one which builds upon a 2-Higgs Doublet Model (2HDM) framework and another which realises a Composite Higgs Model (CHM) through partial compositeness. Such exotic decays of the $t'$ can be competitive with decays into SM particles, leading to new possible discovery channels at the Large Hadron Collider (LHC). Assuming $t'$ pair production via strong interactions, we design signal regions optimised for one $t'\rightarrow S t$ transition (while being inclusive on the other \bar{t'} decay, and vice versa), followed by the decay of $S$ into the two very clean experimental signatures $S\rightarrow γγ$ and $S\rightarrow Z(\rightarrow \ell^+\ell^-)γ$. We perform a dedicated signal-to-background analysis in both channels, by using Monte Carlo (MC) event simulations modelling the dynamics from the proton-proton to the detector level. Under the assumption of BR$(t' \rightarrow S t) = 100\%$, we are therefore able to realistically quantify the sensitivity of the LHC to both the $t'$ and $S$ masses, assuming both current and foreseen luminosities. This approach paves the way for the LHC experiments to surpass current VLQ search strategies based solely on $t'$ decays into SM bosons ($W^\pm, Z$, $h$).

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arXiv2020

Probing the top-Higgs boson FCNC couplings via the $h\to γγ$ channel at the HE-LHC and FCC-hh

We investigate the sensitivity of future searches for the top-Higgs boson Flavour Changing Neutral Current (FCNC) couplings $tqh$~($q= u, c$) at the proposed High Energy Large Hadron Collider~(HE-LHC) and Future Circular Collider in hadron-hadron mode (FCC-hh). We perform a full simulation for two processes in the $h\to γγ$ decay channel (where $h$ is the discovered Higgs state): single top quark FCNC production in association with the Higgs boson (plus a jet) and top quark pair production with FCNC decays $t\to qh$. All the relevant backgrounds are considered in a cut based analysis to obtain the limits on the Branching Ratios (BRs) of $t\to uh$ and $t\to ch$. It is shown that, at the HE-LHC with an integrated luminosity of 15 ab$^{-1}$ and at the FCC-hh with an integrated luminosity of 30 ab$^{-1}$, {{the BR($t\to uh$) (BR($t\to ch$)) can be probed, respectively, to $7.0~(8.5)\times 10^{-5}$ and $2.3~(3.0) \times 10^{-5}$ at the 95\% Confidence Level (CL) (assuming a 10\% systematic uncertainty on the background), which is almost two orders of magnitude better than the current 13 TeV LHC experimental results.

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arXiv2019

Search for single production of a top quark partner via the $T\to th$ and $h\to WW^{\ast}$ channels at the LHC

Many scenarios of physics beyond the Standard Model that address the hierarchy problem also predict the existence of vector-like top quark partners, which are generally expected around the TeV scale. In this paper, we propose to search for a vector-like top quark partner with charge $2/3$ in a simplified model including only two free parameters, the coupling constant $g^{\ast}$ and top quark partner mass $m_T$. We investigate the observability of the top quark partner through the process $pp \to T(\to th)j\to t(\to b W^+\to b \ell^{+} ν_{\ell})h( \to WW^{\ast}\to \ell^{+}ν\ell^{-}\barν) j$, where $T$ is the heavy top quark partner and $h$ the SM-like Higgs boson, at the Large Hadron Collider (LHC). The discovery prospects and exclusion limits on the parameter plane defined by ($m_T,g^{\ast}$) are obtained for the already scheduled LHC runs as well as at the future High-Luminosity~LHC (HL-LHC). The constraints and projected sensitivities are also interpreted in a realistic model, i.e., the minimal Composite Higgs Model with singlet top quark partners. We finally also analyze the projected sensitivity in terms of the production cross section times branching fraction at the (HL-)LHC.

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arXiv2018

Probing anomalous top-Higgs couplings at the HL-LHC via $H\to WW^{\ast}$ decay channels

We study the prospects of probing the anomalous $tHq$~($q= u, c$) couplings via SS2L or 3L signatures at the High Luminosity (HL-LHC) run of the 14 TeV CERN collider. We focus on signals of the $tH$ associated production followed by the decay modes $t\to b\ell^{+}ν_{\ell}$ and $H\to WW^{\ast}$, and $t\bar{t}$ production followed by the decay modes $t\to b\ell^{+}ν_{\ell}$ and $\bar{t}\to H(\to WW^{\ast})\bar{q}$, where $\ell=e, μ$. Based on two types of $H\to WW^{\ast}$ decay topologies, one assuming the semileptonic decay mode $H\to WW^{\ast}\to \ell^{+}νjj $ and the other the fully leptonic decay mode $H\to WW^{\ast}\to \ell^{+}ν\ell^{-}\barν$, we perform a full simulation for signals and backgrounds. It is shown that, at the future HL-LHC, the branching ratio $Br(t\to uh)~(Br(t\to ch))$ can be probed to $1.17~(1.56)\times 10^{-3}$ for the same-sign di-lepton channel and to $7.1~\times 10^{-4}~(1.39~\times 10^{-3})$ for the 3L channel at $3σ$ sensitivity.

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arXiv2017

Searches for anomalous $tqZ$ couplings from the trilepton signal of $tZ$ associated production at the 14 TeV LHC

We investigate the observability of the top anomalous $tqZ$ couplings via the trilepton signatures at the Large Hadron Collider~(LHC) with the center-of-mass energy of 14 TeV. We focus on signals of the $tZ$ associated production with the decay mode $t\to W^{+}b\to b\ell^{+}ν_{\ell}$, $Z\to \ell^{+}\ell^{-}$, and $t\bar{t}$ production with the decay mode $\bar{t}\to Z(\to \ell^{+}\ell^{-})\bar{q}$ and $t\to b\ell^{+}ν_{\ell}$, where $\ell=e, μ$ and $q$ reflects up and charm quarks. It is shown that at $3σ$ level, the FCNC top quark decay branching ratios can be probed at, respectively, about $Br(t\to uZ) \leq 1.3\times 10^{-4}$ and $Br(t\to cZ) \leq 4.2\times 10^{-4}$ with the integrated luminosity of 100 fb$^{-1}$, and probed down to $Br(t\to uZ) \leq 2.2\times 10^{-5}$ and $Br(t\to cZ) \leq 8\times 10^{-5}$ for the high-luminosity LHC with 3000 fb$^{-1}$.

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