arXiv subjects

Liangliang Shang

Publications and source records attributed to Liangliang Shang.

At least 19 recordsLinked to original sources

arXiv2026

Probing the vector-like $X$ quark via the $tW$ channel at future muon-proton colliders

We investigate the discovery potential for the vector-like $X$-quark (VLX) at future muon--proton ($\mu p$) colliders through the process $\mu^+ p \to \bar{\nu}_\mu X \to \bar{\nu}_\mu t W^+$. A simplified effective model is adopted in which the production and decay of the VLX are governed by the coupling strength $g^{*}$, the generation-mixing parameter $R_{L}$, and the VLX mass $m_X$. A comprehensive Monte Carlo analysis is performed at $\sqrt{s}=5.29$, $6.48$, and $9.16\ \mathrm{TeV}$, considering four complementary decay channels: the Fully Leptonic (FL), Fully Hadronic (FH), and two Semi-Leptonic (SL1 and SL2) modes. An $80\%$ polarized muon beam together with boosted-object reconstruction based on fat-jet techniques is employed to improve the signal sensitivity. The expected exclusion and discovery reaches are evaluated using the Asimov significance. We find that the sensitivity can be improved substantially with increasing center-of-mass energy and larger values of $R_L$. Among the four channels, the FH mode provides the strongest sensitivity, reaching a $2\sigma$ exclusion limit of $m_X\simeq8.3\ \mathrm{TeV}$ with $g^* = 0.009 $ for $R_L=0.1$ at $\sqrt{s}=9.16\ \mathrm{TeV}$, whereas the FL mode gives the weakest reach because of its smallest branch ratio. These results demonstrate that future $\mu p$ colliders can offer significant sensitivity to heavy VLX over a broad region of parameter space.

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arXiv2026

Searching for single production of a vector-like $Y$ quark decaying into $bW$ at the FCC-eh

We investigate the exclusion and discovery potential for single production of a vector-like $Y$ quark with electric charge $Q=-4/3$, followed by the decay $Y\to bW$, at the FCC-eh. The $Y$ quark is allowed to couple to both first- and third-generation down-type quarks. The analysis is performed for an electron-beam polarization of $P_e=-80\%$ at $\sqrt{s}=3.46$, $5.29$, and $6.9~\mathrm{TeV}$. Both leptonic and hadronic $W$-boson decay channels are considered. In the hadronic channel, the boosted $W$-boson is reconstructed as a $W$-jet, and kinematic observables are used to suppress the Standard Model (SM) backgrounds. By performing a detailed detector simulations and event analysis, we present the $2\sigma$ exclusion limits and $5\sigma$ discovery reaches in the $g^*$--$m_Y$ plane, where $g^*$ is $Y$ coupling strength to the SM quarks. We find that the hadronic channel can provide stronger exclusion and discovery sensitivities, which are improved with increasing $\sqrt{s}$ at the FCC-eh.

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arXiv2026

Probing Anomalous $t{\bar q}Z$ Interactions at Muon Colliders

In the framework of effective field theory, we study the anomalous $t{\bar q}Z$ interaction through the process $\mu^+\mu^- \to t{\bar q}Z$ at future muon colliders with $\sqrt s= 3, 10, 14\,\text{TeV}$. Based on the top quark decay modes involving $W$ and $Z$ bosons, we first divide the signal into six cases. Then, in order to obtain the limits on the corresponding branching ratios, we perform a detector simulation for both signals and Standard Model backgrounds. To enhance the signal significance, we exploit the polarization of the muon beams and employ the fat jet method to reconstruct signals in hadronic final states. For $\sqrt s= 14\,\text{TeV}$ with $20\,\text{ab}^{-1}$, we find that the upper limit on the branching ratio for $t\to qZ$ can reach the order of $\mathcal{O}(10^{-8})$, which exceeds the limits provided by the CMS and ATLAS collaborations by 2 to 3 orders of magnitude. Our study thus demonstrates that TeV-scale muon colliders can provide an efficient and complementary platform for probing rare top quark interactions.

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arXiv2024

Search for single vector-like $B$ quark production in hadronic final states at the LHC

In this paper, we study the discovery potential of a Vector-Like $B$ quark (VLB) via the process $pp \to B(\to bZ)j\to b(Z \to ν_l\bar{ν_l})j$ at the Large Hadron Collider (LHC) with $\sqrt{s}=14$ TeV. In the framework of a simplified model, we perform a scan over its parameter space and test its viability following a Monte Carlo analysis developed to include all production and decay dynamics. We use cut-and-count combined with Extreme Gradient Boosting (XGBoost) methods to classify the signal and background events in order to improve the efficiency of signal identification and background rejection. We find that this approach can reduce background events significantly while the signal retention rate is much higher than that of traditional methods, thereby improving the VLB discovery potential. We then calculate the exclusion and discovery capabilities for VLBs and find that the advantages of the cut-and-count plus XGBoost method especially lie in the high-mass region, i.e., $m_B > 1500 \text{ GeV}$. We finally obtain the following LHC results in terms of the coupling and chiral structure of a singlet heavy VLB interactions: (i) for $g^{\ast}$=0.2 and $R_L=0$ with 3000 fb$^{-1}$, the $B$ quark mass can be be excluded (discovered) up to 3000 GeV (2500 GeV); (ii) for $g^{\ast}$=0.2 and $R_L=0.5$ with 3000 fb$^{-1}$, the exclusion (discovery) region can reach up to 4750 GeV (4250 GeV).

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arXiv2024

Single production of an exotic vector-like $Y$ quark at future high energy $pp$ colliders

Vector-like quarks have been predicted in various new physics scenarios beyond the Standard Model (SM). In a simplified modelling of a $(B,Y)$ doublet including a vector-like quark $Y$, with charge $-\frac{4}{3}$e, there are only two free parameters: the $Y$ coupling $κ_{Y}$ and mass $m_Y$. In the five flavor scheme, we investigate the single production of the $Y$ state decaying into $Wb$ at the Large Hadron Collider (LHC) Run-III and High-Luminosity LHC (HL-LHC) operating at $\sqrt{s}$ = 14 TeV, the possible High-Energy LHC (HE-LHC) with $\sqrt{s}$ = 27 TeV as well as the Future Circular Collider in hadron-hadron mode (FCC-hh) with $\sqrt{s}$ = 100 TeV. Through detailed signal-to-background analyses and detector simulations, we assess the exclusion capabilities of the $Y$ state at the different colliders. We find that this can be improved significantly with increasing collision energy, especially at the HE-LHC and FCC-hh, both demonstrating an obvious advantage with respect to the HL-LHC in the case of high $m_Y$. Assuming a 10\% systematic uncertainty on the background event rate, the exclusion capabilities are summarized as follows: (1) the LHC Run-III can exclude the correlated regions of $κ_{Y} \in [0.06,0.5]$ and $m_{Y} \in [1500\text{ GeV},3800\text{ GeV}]$ with integrated luminosity $L = 300\text{ fb}^{-1}$; (2) the HL-LHC can exclude the correlated regions of $κ_{Y} \in [0.05,0.5]$ and $m_{Y} \in [1500\text{ GeV},3970\text{ GeV}]$ with $L = 3$ ab$^{-1}$; (3) the HE-LHC can exclude the correlated regions of $κ_Y \in [0.06,0.5]$ and $m_{Y} \in [1500\text{ GeV} , 6090\text{ GeV}]$ with $L = 3$ ab$^{-1}$; (4) the FCC-hh can exclude the correlated regions of $κ_{Y} \in [0.08,0.5]$ and $m_{Y} \in [1500\text{ GeV} , 10080\text{ GeV}]$ with $L = 3$ ab$^{-1}$.

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arXiv2023

EasyScan_HEP: a tool for connecting programs to scan the parameter space of physics models

We present an application, EasyScan_HEP, for connecting programs to scan the parameter space of High Energy Physics (HEP) models using various sampling algorithms. We develop EasyScan_HEP according to the principle of flexibility and usability. EasyScan_HEP allows us to connect different programs that calculate physical observables, and apply constraints by one human-readable configuration file. All programs executed through command lines can be connected to EasyScan_HEP by setting input and output parameters of the programs. The current version offers the sampling algorithms of Random, Grid, Markov chain Monte Carlo and MultiNest. We also implement features such as resume function, parallelization, post-processing, and quick analysis.

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arXiv2023

Properties of Heavy Higgs Bosons and Dark Matter under Current Experimental Limits in the $μ$NMSSM

Searches for new particles beyond the Standard Model (SM) are an important task for the Large Hadron Collider (LHC). In this paper, we investigate the properties of the heavy non-SM Higgs bosons in the $μ$-term extended Next-to-Minimal Supersymmetric Standard Model ($μ$NMSSM). We scan the parameter space of the $μ$NMSSM considering the basic constraints from Higgs data, dark matter (DM) relic density, and LHC searches for sparticles. And we also consider the constraints from the LZ2022 experiment and the muon anomaly constraint at 2$σ$ level. We find that the LZ2022 experiment has a strict constraint on the parameter space of the $μ$NMSSM, and the limits from the DM-nucleon spin-independent (SI) and spin-dependent (SD) cross-sections are complementary. Then we discuss the exotic decay modes of heavy Higgs bosons decaying into SM-like Higgs boson. We find that for doublet-dominated Higgs $h_3$ and $A_2$, the main exotic decay channels are $h_3\rightarrow Z A_1$, $h_3\rightarrow h_1 h_2$, $A_2\rightarrow A_1 h_1$ and $A_2\rightarrow Z h_2$, and the branching ratio can reach to about 23$\%$, 10$\%$, 35$\%$ and 10$\%$ respectively. At the 13 TeV LHC, the production cross-section of $ggF\rightarrow h_3\rightarrow h_1 h_2$ and $ggF\rightarrow A_2\rightarrow A_1 h_1$ can reach to about $10^{-11}$pb and $10^{-10}$pb, respectively.

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arXiv2023

Search for the singlet vector-like top quark in the $T\to tZ$ channel with $Z\to ν\barν$ at hadron colliders

Based on a simplified model including a singlet vector-like top quark $T$ with charge $|Q|=2/3$, we analyze the prospects of observing $T$ via the single $T$ production in the $tZ$ channel with $Z$ decaying to neutrinos at the hadron-hadron colliders. This simplified model only includes two free parameters, the coupling constant $g^*$ and the $T$ quark mass $m_T$. To investigate the observability of the single $T$ production, we perform a detailed background analysis and detector simulation for the collision energies 14~TeV, 27~TeV, and 100~TeV. We scan the $g^*-m_T$ parameter space and show the exclusion and discovery capabilities on the $T$ quark with the highest integrated luminosity designed at these colliders. Moreover, the limits from the narrow-width approximation and electroweak precision observables are considered.

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arXiv2023

The Phenomenological Research on Higgs and dark matter in the Next-to-Minimal Supersymmetric Standard Model

The $Z_3$-invariant next-to-minimal supersymmetric standard model (NMSSM) can provide a candidate for dark matter (DM). It can also be used to explain the hypothesis that the Higgs signal observed on the Large Hadron Collider (LHC) comes from the contribution of the two lightest CP-even Higgs bosons, whose masses are near 125 GeV. At present, XENON1T, LUX, and PandaX experiments have imposed very strict restrictions on direct collision cross sections of {dark matter}. In this paper, we consider a scenario that the observed Higgs signal is the superposition of two mass-degenerate Higgs in the $Z_3$-invariant NMSSM and scan the seven-dimension parameter space composing of $λ, κ, \tanβ, μ, A_k, A_t, M_1$ via the Markov chain Monte Carlo (MCMC) method. We find that the DM relic density, as well as the LHC searches for sparticles, especially the DM direct detections, has provided a strong limit on the parameter space. %Please check intended meaning has been retained. The allowed parameter space is featured by a relatively small $μ\le 300$ GeV and about $\tanβ\in(10,20)$. In addition, the DM is Higgsino-dominated because of $|\frac{2κ}λ|>1$. Moreover, the co-annihilation between $\tildeχ_1^0$ and $\tildeχ_1^\pm$ must be taken into account to obtain the reasonable DM relic density.

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arXiv2022

Interpreting the $W$ mass anomaly in the vector-like quark models

The new measurement of $W$-boson mass by the CDF collaboration revealed a remarkable $7σ$ disagreement with the Standard Model (SM) prediction. If confirmed by other experiments, then the disagreement strongly indicates the existence of new physics beyond the SM. In this work, seven vectorlike quark (VLQ) extensions of the SM are investigated to interpret the anomaly, and it is found that three can explain the anomaly in broad parameter space. The explanations are consistent with the constraints from oblique parameters, the LHC search for VLQs, the measurements of the properties for the top quark, bottom quark, and Higgs boson, and the perturbativity criterion. The typical size of the involved Yukawa coupling is around 1, which is comparable to the top quark Yukawa coupling in the SM. The other extensions, however, either predict a negative correction to the mass in reasonable parameter space or explain the anomaly by unnatural theoretical input parameters.

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arXiv2022

Interpreting the $W$-mass anomaly in the vectorlike quark models

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arXiv2022

The mass-degenerate SM-like Higgs and anomaly of $(g-2)_μ$ in $μ$-term extended NMSSM

We chose the $μ$-term extended next-to-minimal supersymmetric standard model ($μ$NMSSM) for this work, and the phenomenological research is based on the assumption of double Higgs resonance state as the Standard Model (SM)-like Higgs considering the recent $(g-2)_μ$ result. The study also take into account a variety of experimental results, including direct detection of dark matter (DM) and searching results for sparticles at the Large Hadron Collider (LHC). We study the characteristic of DM confronted with limitations of direct detection experiments. Following that, we concentrate on the properties of the mass-degenerate SM-like Higgs bosons and explaining the anomaly of $(g-2)_μ$. We conclude that the anomaly of $(g-2)_μ$ can be explained in the scenario with two mass-degenerate SM-like Higgs, and there are samples that meet all current constraints and outperform SM in fitting Higgs data.

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arXiv2019

A Bayesian analysis of sneutrino DM in the NMSSM with Type-I seesaw mechanism

In the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with extra heavy neutrino superfields, neutrino may acquire its mass via a seesaw mechanism and sneutrino may act as a viable dark matter (DM) candidate. Given the strong tension between the naturalness for $Z$ boson mass and the DM direct detection experiments for customary neutralino DM candidate, we augment the NMSSM with Type-I seesaw mechanism, which is the simplest extension of the theory to predict neutrino mass, and study the scenarios of sneutrino DM. We construct likelihood function with LHC Higgs data, B-physics measurements, DM relic density and its direct and indirect search limits, and perform a comprehensive scan over the parameter space of the theory by Nested Sampling method. We adopt both Bayesian and frequentist statistical quantities to illustrate the favored parameter space of the scenarios, the DM annihilation mechanism as well as the features of DM-nucleon scattering. We find that the scenarios are viable over broad parameter regions, especially the Higgsino mass $μ$ can be below about $250 {\rm GeV}$ for a significant part of the region, which predicts $Z$ boson mass in a natural way. We also find that the DM usually co-annihilated with the Higgsinos to get the measured relic density, and consequently the DM-nucleon scattering rate is naturally suppressed to coincide with the recent XENON-1T results even for light Higgsinos. Other issues, such as the LHC search for the Higgsinos, are also addressed.

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arXiv2019

Current Status of Natural NMSSM in Light of LHC 13TeV Data and XENON-1T Results

In the natural realization of the Next-to-minimal Supersymmetric Standard Model, Higgsinos tend to be lighter than about several hundred GeVs, which can induce detectable leptonic signals at the LHC as well as large DM-nucleon scattering cross section. We explore the constraints from the direct searches for electroweakino and slepton at the LHC Run II and the latest DM direct detection experiments on the scenario with low fine tuning indicator $Δ_{Z/h} \leq 50$. We find that these experiments are complementary to each other in excluding the scenario, and as far as each kind of experiment is concerned, it is strong enough to exclude a large portion of the parameter space. As a result, the scenario with Bino- or Higgsino-dominated DM is disfavored, and that with Singlino-dominated DM is tightly limited. There are two regions in natural NMSSM parameter space surviving in the current experimental limits. One is featured with a decoupled Singlino-dominated LSP with $μ\simeq m_{\widetildeχ_1^0}$, which cannot be explored by neither DM detections or collider searches. The other parameter space region is featured by $10^{-47}~{\rm cm^2} \lesssim σ^{SI}_{\widetildeχ-p} \lesssim 10^{-46}~{\rm cm^2}$ and the correlation $μ\simeq m_{\widetildeχ_1^0}$, which will be explored by near future DM detection experiments.

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arXiv2018

Explaining the DAMPE data with scalar dark matter and gauged $U(1)_{L_e-L_μ}$ interaction

Inspired by the peak structure observed by recent DAMPE experiment in $e^+e^-$ cosmic-ray spectrum, we consider a scalar dark matter (DM) model with gauged $U(1)_{L_e-L_μ}$ symmetry, which is the most economical anomaly-free theory to potentially explain the peak by DM annihilation in nearby subhalo. We utilize the process $χχ\to Z^\prime Z^\prime \to l \bar{l} l^\prime \bar{l}^\prime$, where $χ$, $Z^\prime$, $l^{(\prime)}$ denote the scalar DM, the new gauge boson and $l^{(\prime)} =e, μ$, respectively, to generate the $e^+e^-$ spectrum. By fitting the predicted spectrum to the experimental data, we obtain the favored DM mass range $m_χ\simeq 3060^{+80}_{-100} \, {\rm GeV}$ and $Δm \equiv m_χ- m_{Z^\prime} \lesssim 14 \, {\rm GeV}$ at $68\%$ Confidence Level (C.L.). Furthermore, we determine the parameter space of the model which can explain the peak and meanwhile satisfy the constraints from DM relic abundance, DM direct detection and the collider bounds. We conclude that the model we consider can account for the peak, although there exists a tension with the constraints from the LEP-II bound on $m_{Z^\prime}$ arising from the cross section measurement of $e^+e^- \to Z^{\prime\ast} \to e^+ e^-$.

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arXiv2018

Interpretations of galactic center gamma-ray excess confronting the PandaX-II constraints on dark matter-neutron spin-dependent scatterings in the NMSSM

The Weakly Interacting Massive Particle (WIMP) has been one of the most attractive candidates for Dark Matter (DM), and the lightest neutralino ($\widetildeχ^0_1$) in the Next-to-Minimal Supersymmetric Standard Model (NMSSM) is an interesting realization of WIMP. The Galactic Center Excess (GCE) can be explained by WIMP DM annihilations in the sky. In this work we consider the $Z_3$-NMSSM where the singlet $S$ and Singlino $\widetilde{S}^0$ components play important roles in the Higgs and DM sector. Guided by our analytical arguments, we perform a numerical scan over the NMSSM parameter space for the GCE explanation by considering various observables such as the Standard Model (SM) Higgs data measured by the ATLAS and CMS experiments, and the $B$-physics observables $BR(B_s\rightarrow X_sγ)$ and $BR(B_s\rightarrow μ^+μ^-)$. We find that the correlation between the coupling $C_{A_1 b\bar{b}}$ in $\langle σ_{b\bar{b}} v \rangle _{0}$ and the coupling $C_{Z \widetildeχ^0_1 \widetildeχ^0_1}$ in DM-neutron Spin Dependent (SD) scattering rate $σ^{SD}_{\widetildeχ^0_1-N}$ makes all samples we obtain for GCE explanation get excluded by the PandaX-II results. Although the DM resonant annihilation scenarios may be beyond the reach of our analytical approximations and scan strategy, the aforementioned correlation can be a reasonable motivation for future experiments such as PandaX-nT to further test the NMSSM interpretation of GCE.

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arXiv2018

Scalar dark matter explanation of the DAMPE data in the minimal Left-Right symmetric model

Left-Right symmetric model (LRSM) has been an attractive extension of the Standard Model (SM) which can address the origin of parity violation in the SM electroweak (EW) interactions, generate tiny neutrino masses, accommodate dark matter (DM) candidates and provide a natural framework for baryogenesis through leptogenesis. In this work we utilize the minimal LRSM to study the recently reported DAMPE results of cosmic $e^+e^-$ spectrum which exhibits a tentative peak around 1.4 TeV, while satisfying the current neutrino data. We propose to explain the DAMPE peak with a complex scalar DM $χ$ in two scenarios: 1) $χχ^* \to H_1^{++}H_1^{--} \to \ell_i^+\ell_i^+\ell_j^-\ell_j^-$; 2) $χχ^* \to H_{k}^{++}H_{k}^{--} \to \ell_i^+\ell_i^+\ell_j^-\ell_j^-$ accompanied by $χχ^* \to H_1^+ H_1^- \to \ell_i^+ ν_{\ell_i} \ell_j^- ν_{\ell_j}$ with $\ell_{i,j}=e,μ,τ$ and $k=1,2$. We fit the theoretical prediction on $e^+e^-$ spectrum to relevant experimental data to determine the scalar mass spectrum favored by the DAMPE excess. We also consider various constraints from theoretical principles, collider experiments as well as DM relic density and direct search experiments. We find that there are ample parameter space which can interpret the DAMPE data while passing the constraints. Our explanations, on the other hand, usually imply the existence of other new physics at the energy scale ranging from $10^7 {\rm GeV}$ to $10^{11} {\rm GeV}$. Collider tests of our explanations are also discussed.

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arXiv2018

Scalar dark matter interpretation of the DAMPE data with U(1) gauge interactions

Recently, DAMPE experiment released the new measurement of the total cosmic $e^+e^-$ flux between 25 GeV and 4.6 TeV which indicates a spectral softening at around 0.9 TeV and a tentative peak at around 1.4 TeV. We utilize the scalar dark matter (DM) annihilation scenario to explain the DAMPE peak by extending $G_{SM}\equiv SU(3)_C \times SU(2)_L \times U(1)_Y$ with additional $U(1)$ gauge symmetries while keeping anomaly free to generate $χχ\to Z^\prime Z^\prime \to \ell\bar{\ell}\ell^\prime\overline{\ell^\prime}$, where $χ, Z^\prime, \ell^{(^\prime)}$ denote the scalar DM, the new gauge boson and $\ell^{(^\prime)}=e,μ,τ$, respectively, with $m_χ\sim m_{Z^\prime} \sim 2 \times 1.5$ (TeV). We first illustrate that the minimal framework $G_{SM} \times U(1)_{Y^\prime}$ with the above mass choices can explain the DAMPE excess but has been excluded by LHC constraints from the $Z^\prime$ searches. Then we study a non-minimal framework $G_{SM} \times U(1)_{Y^\prime} \times U(1)_{Y^{\prime \prime}}$ in which $U(1)_{Y^{\prime \prime}}$ mixes with $U(1)_{Y^\prime}$. We show that such a framework can interpret the DAMPE data while passing other constraints including the DM relic abundance, DM direct detection and collider bounds. We also investigate the predicted $e^+e^-$ spectrum in this framework and find that the mass splitting $Δm = m_χ- m_{Z'}$ should be less than about 17 GeV to produce the peak-like structure.

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