arXiv subjects

Jae Sik Lee

Publications and source records attributed to Jae Sik Lee.

At least 19 recordsLinked to original sources

arXiv2026

Quantum entanglement and Bell nonlocality in top-quark pair production at a photon linear collider

A photon linear collider, the two-photon collision mode of an $e^+e^-$ linear collider, uses high-energy laser photons backscattered off the incoming electrons and positrons. The colliding-photon polarization is fully controllable through the polarizations of the initial electron and positron beams and laser photons. We investigate the impact of colliding-photon polarization on the observability of quantum entanglement in top-quark pair production at a photon linear collider. Constructing the spin density matrix of the $t\bar{t}$ two-qubit system from the helicity amplitudes, we demonstrate that a photon linear collider is an ideal machine to probe quantum entanglement and Bell nonlocality across the broad phase space of the process.

hep-ph↗

arXiv2026

Measuring the trilinear Higgs self-coupling in Higgs boson pair production at multi-TeV muon colliders

The trilinear Higgs self-coupling determines the shape of the Higgs potential, and its measurement is a central goal of future colliders. We assess the sensitivity of multi-TeV muon colliders to the coupling modifier $κ_3$ in Higgs boson pair production via vector boson fusion, using the $b\bar{b}b\bar{b}$ final state at $\sqrt{s}=3$ TeV with $1$ ab$^{-1}$ and at $10$ TeV with $10$ ab$^{-1}$. Events are analyzed in two complementary regions, a resolved region with four jets and a boosted region with two large-radius jets. To extract the signal from backgrounds a few orders of magnitude larger, we combine a supervised jet-to-Higgs pairing network based on the SPANet approach, topological data analysis of the event energy flow, and two dedicated classifiers, $D_{\rm HH}$ for the signal-to-background separation and $D_{κ_3}$ for the $κ_3$ shape information. The coupling is extracted from a two-dimensional likelihood fit to the distribution of the two classifier outputs. Combining the two regions, we obtain $0.80<κ_3<1.29$ at $3$ TeV and $0.96<κ_3<1.05$ at $10$ TeV at $68\%$ confidence level. The $10$ TeV determination reaches the few-percent level in this statistics-limited projection, which surpasses by a large amount the precision projected for the HL-LHC.

hep-ph↗

arXiv2026

Characterization of the 20-inch Photomultiplier Tubes for RENE Detector

To address the Reactor Antineutrino Anomaly (RAA) observed in neutrino experiments, the Reactor Experiment for Neutrino and Exotics (RENE) has been initiated using a liquid scintillation detector. In this study, we investigate the characteristics of two 20-inch Hamamatsu R12860 photomultiplier tubes (PMTs) intended for installation in the RENE detector. The charge and timing responses of the PMTs were evaluated at both the nominal and target gains expected during actual operation. In particular, gain non-uniformity arising from the large-diameter photocathode with a box-and-line type dynode structure was examined, and the maximum gain variation was measured. The occurrence rate, timing, and charge distributions of late pulses and afterpulses were also investigated to characterize the specific response features of the R12860 PMT. The results reported in this study will aid in the interpretation of signals from the RENE detector and serve as a reference for estimating potential systematic uncertainties in RENE data. Furthermore, these findings are expected to provide valuable information for other experiments employing the same type of PMTs.

physics.ins-det↗

arXiv2025

RENE experiment for the sterile neutrino search using reactor neutrinos

This paper summarizes the details of the Reactor Experiment for Neutrinos and Exotics (RENE) experiment. It covers the detector construction, Monte Carlo (MC) simulation study, and physics expectations. The primary goal of the RENE project is to investigate the sterile neutrino oscillation at $Δ{m}^{2}_{41}\sim 2\,{\rm{eV}^{2}}$. which overlap with the allowed region predicted by the Reactor Antineutrino Anomaly (RAA). On the other hand, the STEREO and PROSPECT experiments have excluded certain regions of the parameter space with 95 \% confidence level (C.L.), while the joint study conducted by RENO and NEOS suggests possible indications of sterile neutrinos at $Δ{m}^{2}_{41}\sim2.4\,{\rm{eV}^{2}}$ and $\sim{1.7}{\,\rm{eV}^{2}}$ with sin$^{2}θ_{41} < 0.01$. Accordingly, a more meticulous investigation of these remaining regions continues to be a scientifically valuable endeavor. This paper reports the technical details of the detector and physics objectives.

hep-ex↗

arXiv2025

Higgs boson precision analysis of two-Higgs-doublet models: Full LHC Run 1 and Run 2 data

We present the results obtained by performing global fits of two-Higgs-doublet models (2HDMs) using the full Run 1 and Run 2 Higgs datasets collected at the LHC. Avoiding unwanted tree-level flavor-changing neutral currents and including the wrong-sign cases, we consider 12 scenarios across six types of 2HDMs: Inert, type I, type II, type III, type IV, and Aligned 2HDMs. Our main results are presented in Table III and Fig. 1. We find that the type-I 2HDM provides the best fit, while the wrong-sign scenarios of the type-II and type-IV 2HDMs, where the normalized Yukawa coupling to down-type quarks is opposite in sign to the Standard Model (SM), are disfavored. We also observe that the Aligned 2HDM gives the second-best fit when the Yukawa couplings to down-type quarks take the same sign as in the SM, regardless of the sign of the Yukawa couplings to the charged leptons.

hep-ph↗

arXiv2024

Higgs Boson Precision Analysis of the Full LHC Run 1 and Run 2 Data

We perform global fits of the Higgs boson couplings to the full Higgs datasets collected at the LHC with the integrated luminosities per experiment of approximately 5/fb at 7 TeV, 20/fb at 8 TeV, and up to 139/fb at 13 TeV. Our combined analysis based on the experimental signal strengths used in this work and the theoretical ones elaborated for our analysis reliably reproduce the results in the literature. We reveal that the LHC Higgs precision data are no longer best described by the SM Higgs boson taking account of extensive and comprehensive CP-conserving and CP-violating scenarios found in several well-motivated models beyond the SM. Especially, in most of the fits considered in this work, we observe that the best-fitted values of the normalized Yukawa couplings are about $2σ$ below the corresponding SM ones with the $1σ$ errors of 3%-5%. On the other hand, the gauge-Higgs couplings are consistent with the SM with the $1σ$ errors of 2%-3%. Incidentally, the reduced Yukawa couplings help to explain the excess of the $H\to Zγ$ signal strength of $2.2\pm 0.7$ recently reported by the ATLAS and CMS collaborations.

hep-ph↗

arXiv2023

On the mass spectrum of heavy Higgs bosons in two-Higgs-doublet model in the light of the CDF $W$-mass anomaly

We analyze the mass spectrum of the charged and neutral Higgs bosons in the framework of two Higgs doublet model (2HDM) in the light of the precision measurement of the $W$ boson mass by the CDF collaboration. We have considered the most general 2HDM potential with explicit CP violation in the Higgs basis which contains the three CP-mixed neutral mass eigenstates $H_1$, $H_2$, and $H_3$ with $M_{H_1}\leq M_{H_2}\leq M_{H_3}$. The high-precision CDF measurement of the $W$ boson mass is characterized by the large positive value of the $T$ parameter. By identifying the lightest neutral Higgs boson $H_1$ as the SM-like one discovered at the LHC, we find that it is necessary to have the mass splitting between the charged Higgs boson $H^\pm$ and the second heaviest neutral one $H_2$ to accommodate the sizable positive deviation of the $T$ parameter from its SM value of $0$. By combining the mass splitting between $H^\pm$ and $H_2$ with the theoretical constraints from the perturbative unitarity and for the Higgs potential to be bounded from below, we implement comprehensive analysis of the mass spectrum of the heavy Higgs bosons taking account of the effects of deviation from the alignment limit and also the mass splitting between $H_3$ and $H_2$. We further analyze the behavior of the heavy-Higgs mass spectrum according to the variation of the $T$ parameter. Finally, concentrating on the heavy mass region $M\equiv (M_{H_2}+M_{H^\pm})/2\gsim 500$ GeV in which we find a mass hierarchy of $M\gg M_{H_1}\sim |Δ| \gsim δ$ with $Δ\equiv M_{H_2}-M_{H^\pm}$ and $δ\equiv M_{H_3}-M_{H_2}$, we discuss some benchmarking scenarios for the searches of heavy Higgs bosons at future colliders such as the high luminosity option of the LHC and a 100 TeV hadron collider.

hep-ph↗

arXiv2022

Yukawa Alignment Revisited in the Higgs Basis

We implement a comprehensive and detailed study of the alignment of Yukawa couplings in the so-called Higgs basis taking the framework of general two Higgs doublet models (2HDMs). We clarify the model input parameters and derive the Yukawa couplings considering the two types of CP-violating sources: one from the Higgs potential and the other from the three complex alignment parameters $ζ_{f=u,d,e}$. We consider the theoretical constraints from the perturbative unitarity and for the Higgs potential to be bounded from below as well as the experimental ones from electroweak precision observables. Also considered are the constraints on the alignment parameters from flavor-changing $τ$ decays, $Z\to b\bar b$, $ε_K$, and the radiative $b\to sγ$ decay. By introducing the basis-independent Yukawa delay factor $Δ_{H_1\bar f f}\equiv |ζ_{f}|(1-g_{_{H_1VV}}^2)^{1/2}$, we scrutinize the alignment of the Yukawa couplings of the lightest Higgs boson to the SM fermions.

hep-ph↗

arXiv2022

Impact of the CDF $W$-mass anomaly on two Higgs doublet model

We consider the implication of the recent CDF $W$-mass anomaly in the general framework of two Higgs doublet model. We find that the large deviation of the $S$ and $T$ parameters from their SM values of zero leads to the upper limit of about $1$ TeV on the heavy charged and neutral Higgs bosons when it is combined with the theoretical constraints from the perturbative unitarity and for the Higgs potential to be bounded from below.

hep-ph↗

arXiv2021

Decays of Higgs Bosons in the Standard Model and Beyond

We make an updated review and a systematic and comprehensive analysis of the decays of Higgs bosons in the Standard Model (SM) and its three well-defined prototype extensions such as the complex singlet extension of the SM (cxSM), the four types of two Higgs-doublet models (2HDMs) without tree-level Higgs-mediated flavor-changing neutral current (FCNC) and the minimal supersymmetric extension of the SM (MSSM). We summarize the theoretical predictions for the decay widths of the SM Higgs boson and those of Higgs bosons appearing in its extensions taking account of all possible decay modes. We incorporate them to study and analyze decay patterns of CP-even, CP-odd, and CP-mixed neutral Higgs bosons and charged ones. We put special focus on the properties of a neutral Higgs boson with mass about 125 GeV discovered at the LHC and present constraints obtained from precision analysis of it. This review is intended to be self-contained and consolidated by coherently integrating relevant physics information for studying decays of Higgs bosons in the SM and beyond.

hep-ph↗

arXiv2020

Alignment of Yukawa couplings in two Higgs doublet models

We study the alignment of Yukawa couplings in the framework of general two Higgs doublet models (2HDMs) considering a scenario in which the lightest neutral Higgs boson is purely CP even while the two heavier neutral Higgs bosons are allowed to mix in the presence of nontrivial CP-violating phases in the Higgs potential. Identifying the lightest neutral Higgs boson as the 125 GeV one discovered at the LHC, we find that the alignment of Yukawa couplings without decoupling could be easily achieved in the type-I 2HDM with no much conflict with the current LHC Higgs precision data. Otherwise, we observe that the Yukawa couplings of the lightest Higgs boson could decouple much slowly compared to the Higgs coupling to a pair of massive vector bosons and they significantly deviate from the corresponding SM values even when the deviation of the Higgs to vector boson coupling is below the percent level. On the other hand, independently of 2HDM type and regardless of decoupling, we find a wrong-sign alignment limit of the Yukawa couplings in which the Yukawa couplings to the down-type quarks and/or those to the charged leptons are equal in strength but opposite in sign to the corresponding SM ones. The magnitude and sign of the up-type quark Yukawa couplings remain the same as in the SM. Accordingly, in this limit, all four types of 2HDMs are viable against the LHC Higgs precision data.

hep-ph↗

arXiv2020

Measuring the trilinear Higgs boson self--coupling at the 100 TeV hadron collider via multivariate analysis

We perform a multivariate analysis of Higgs-pair production via the decay channel $HH \to b\bar b γγ$ at the future 100 TeV $pp$ collider to determine the trilinear Higgs self--coupling (THSC) $λ_{3H}$, which takes the value of 1 in the standard model. We consider all known background processes. For the signal we adopt the most recent event generator of {\tt POWHEG-BOX-V2} to exploit the NLO distributions for Toolkit for Multivariate Data Analysis (TMVA). Through the technique of Boosted Decision Tree (BDT) analysis trained for $λ_{3H}=1$, compared to the the conventional cut-and-count approach, the signal-to-background ratio improves tremendously from about $1/10$ to $1$ and the significance can reach up to $20.5$ with a luminosity of 3 ab$^{-1}$ without including systematic uncertainties. In addition, by implementing a likelihood fitting of the signal-plus-background $M_{γγb b}$ distribution with optimized bin sizes, it is possible to determine the THSC with the precision of 7.5\% at 68\% CL even at the early stage of 100 TeV hadron collider with 3 ab$^{-1}$.

hep-ph↗

arXiv2019

Probing Trilinear Higgs Self-coupling at the HL-LHC via Multivariate Analysis

We perform a multivariate analysis of Higgs-pair production in $HH \to b\bar b γγ$ channel at the HL-LHC to probe the trilinear Higgs self--coupling $λ_{3H}$, which takes the value of 1 in the SM. We consider all the known background processes. Also, for the signal we are the first to adopt the most recent event generator of POWHEG-BOX-V2 to exploit the NLO distributions for Toolkit for Multivariate Data Analysis (TMVA), taking account of the full top--quark mass dependence. Through Boosted Decision Tree (BDT) analysis trained for $λ_{3H}=1$, we find that the significance can reach up to 1.95 with about $9$ signal and $18$ background events. In addition, the Higgs boson self-coupling can be constrained to $1.00 < λ_{3H} < 6.22$ at 95\% confidence level (CL). We also perform a likelihood fitting of $M_{γγbb}$ distribution and find the $1σ$ confidence interval (CI) of $0.1 < λ_{3H} < 2.2\, \cup\,5.4 < λ_{3H} < 6.6$ for the $λ_{3H}=1$ nominal set. On the other hand, using BDTs trained for each value of $λ_{3H}$, we find a bulk region of $0.5 <\sim λ_{3H} <\sim~ 4.5$, for which it is hard to pin down the trilinear coupling.

hep-ph↗

arXiv2019

New Emerging Results in Higgs Precision Analysis Updates 2018 after Establishment of Third-Generation Yukawa Couplings

We perform global fits of the Higgs boson couplings to all the 7 TeV, 8 TeV, and 13 TeV data available up to the Summer 2018. New measurements at 13 TeV extend to include the Higgs signal strengths exclusively measured in associated Higgs production with top-quark pair and the third-generation Yukawa couplings now have been established. Some important consequences emerge from the global fits. (i) The overall average signal strength of the Higgs boson stands at $2σ$ above the SM value ($μ= 1.10 \pm 0.05 $). (ii) For the first time the bottom-quark Yukawa coupling shows a preference of the positive sign to the negative one. (iii) The negative top-quark Yukawa coupling is completely ruled out unless there exist additional particles running in the $H$-$γ$-$γ$ loop with contributions equal to two times the SM top-quark contribution within about 10 \%. (iv) The branching ratio for nonstandard decays of the Higgs boson is now below 8.4\% at the 95\% confidence level.

hep-ph↗

arXiv2019

Higgs-boson-pair production $H(\rightarrow b\overline{b})H(\rightarrowγγ)$ from gluon fusion at the HL-LHC and HL-100 TeV hadron collider

We perform the most up-to-date comprehensive signal-background analysis for Higgs-pair production in $HH \to b\bar b γγ$ channel at the HL-LHC and HL-100 TeV hadron collider, with the goal of probing the self-coupling $λ_{3H}$ of the Higgs boson. We simulate all the standard-model signal and background processes with the simulation tools almost as sophisticated as what experimentalists are using. We find that even for the most promising channel $HH \to b\bar{b}γγ$ at the HL-LHC with a luminosity of 3000 fb$^{-1}$, the significance is still not high enough to establish the Higgs self-coupling at the standard model (SM) value. Instead, we can only constrain the self-coupling to $-1.0 < λ_{3H} < 7.6 $ at $ 95\% $ confidence level after considering the uncertainties associated with the top-Yukawa coupling and the estimation of backgrounds. Here we also extend the study to the HL-100 TeV hadron collider. With a luminosity of 3 ab$^{-1}$, we find there exists a bulk region of $2.6 \lsim λ_{3H} \lsim 4.8 $ in which one cannot pin down the trilinear coupling. Otherwise one can measure the coupling with a high precision. At the SM value, for example, we show that the coupling can be measured with about 20 \% accuracy. While assuming 30 ab$^{-1}$, the bulk region reduces to $3.1 \lsim λ_{3H} \lsim 4.3$ and the trilinear coupling can be measured with about 7 \% accuracy at the SM value. With all the simulated background events and results, our study can be useful to probe the Higgs potential of various models with extended Higgs sector, such as two-Higgs-doublet model, MSSM, etc.

hep-ph↗

arXiv2019

Vector-like Quark Interpretation of Excess in Higgs Signal Strength

There is a $+2σ$ deviation in the average Higgs-signal strength for all the $7+8+13$ TeV data up to Summer 2018. We find that a slight reduction of the bottom-Yukawa coupling can fit the data better than the standard model. We suggest an extension with a vector-like quark doublet, of which the right-handed component of $b'$ mixes nonnegligibly with the standard model $b$ quark. We show that the mixing would induce a reduction of the bottom Yukawa coupling. Simultaneously, the coupling of the $Z$ boson to the right-handed $b$ quark increases, which could reduce the forward-backward asymmetry of bottom production at LEP and bring it closer to the experimental value.

hep-ph↗

arXiv2018

Measuring properties of a Heavy Higgs boson in the $H\to t\bar t \to bW^+\bar b W^-$ decay

Suppose a heavy neutral Higgs or scalar boson $H$ is discovered at the LHC, it is important to investigate its couplings to the standard model particles as much as possible. Here in this work we attempt to probe the CP-even and CP-odd couplings of the heavy Higgs boson to a pair of top quarks, through the decay $H \to t\bar t \to b W^+ \bar b W^-$. We use the helicity-amplitude method to write down the most general form for the angular distributions of the final-state $b$ quarks and $W$ bosons. We figure out that there are 6 types of angular observables and, under CP$\widetilde{\rm T}$ conservation, one-dimensional angular distributions can only reveal two of them. Nevertheless, the $H$ couplings to the $t\bar t$ pair can be fully determined by exploiting the one-dimensional angular distributions. A Higgs-boson mass of 380 GeV not too far above the $t\bar t$ threshold is illustrated with full details. With a total of $10^4$ events of $H \to t\bar t \to bW^+ \bar b W^+$, one can determine the couplings up to 10-20 % uncertainties.

hep-ph↗

arXiv2017

Measuring properties of a Heavy Higgs boson in the $H\to ZZ \to 4\ell$ decay

In many extensions of the standard model, there exist a few extra Higgs bosons. Suppose a heavy neutral Higgs boson H is discovered at the LHC, one could then investigate CP and CPT~ properties of its couplings to a pair of $Z$ bosons through $H \to ZZ \to 4\ell$. We use the helicity-amplitude method to write down the most general form for the angular distributions of the four final-state leptons, which can cover the case of CP-even, -odd, and -mixed state for the Higgs boson. We figure out there are 9 types of angular observables and all the $H$ couplings to $Z$ bosons can be fully determined by exploiting them. A Higgs-boson mass of 260 GeV below the $t\bar t$ threshold is illustrated with full details. With a total of $10^3$ events of $H \to ZZ \to 4\ell$, one can determine the couplings up to 12-20\% uncertainties.

hep-ph↗