arXiv subjects

Jung Chang

Publications and source records attributed to Jung Chang.

At least 19 recordsLinked to original sources

arXiv2025

Demonstrating Interoperable Channel State Feedback Compression with Machine Learning

Neural network-based compression and decompression of channel state feedback has been one of the most widely studied applications of machine learning (ML) in wireless networks. Various simulation-based studies have shown that ML-based feedback compression can result in reduced overhead and more accurate channel information. However, to the best of our knowledge, there are no real-life proofs of concepts demonstrating the benefits of ML-based channel feedback compression in a practical setting, where the user equipment (UE) and base station have no access to each others' ML models. In this paper, we present a novel approach for training interoperable compression and decompression ML models in a confidential manner, and demonstrate the accuracy of the ensuing models using prototype UEs and base stations. The performance of the ML-based channel feedback is measured both in terms of the accuracy of the reconstructed channel information and achieved downlink throughput gains when using the channel information for beamforming. The reported measurement results demonstrate that it is possible to develop an accurate ML-based channel feedback link without having to share ML models between device and network vendors. These results pave the way for a practical implementation of ML-based channel feedback in commercial 6G networks.

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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$^{-1}$.

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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.

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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.

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arXiv2018

Sneutrino Dark Matter via pseudoscalar X-funnel meets Inverse Seesaw

In this paper we study sneutrino dark matter in a recently proposed supersymmetric electroweak-scale inverse seesaw model, in which the majority of the sneutrino dark matter particle is a mixture of the right-handed sneutrino $\tilde{N}^c$ and the singlet field $\tilde{S}$. The scalar field $X$ responsible for the generation of neutrino masses can simultaneously play a crucial role for sneutrino annihilation in the early Universe via the pseudoscalar mediator $A_X$ into neutrinos. We focus here on the dominant annihilation channels and provide all the formulas together with analytic estimates in order to identify the relevant parameters. Furthermore, we show that the direct detection scattering cross section is many orders of magnitude below the current limits, and estimate the indirect detection annihilation rate, which is only a few orders of magnitude below the current limits.

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arXiv2018

Proceedings of the first MadAnalysis 5 workshop on LHC recasting in Korea

We present the activities performed during the first MadAnalysis 5 workshop on LHC recasting that has been organized at High 1 (Gangwon privince, Korea) on August 20-27, 2017. This report includes details on the implementation in the MadAnalysis 5 framework of eight ATLAS and CMS analyses, as well as a description of the corresponding validation and the various issues that have been observed.

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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.

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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.

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arXiv2017

A supersymmetric electroweak scale seesaw model

In this paper we propose a novel supersymmetric inverse seesaw model which has only one additional $Z_6$ symmetry. The field content is minimal to get a viable neutrino spectrum at tree-level. Interestingly, the inverse seesaw scale in our model is related to the scale of electroweak symmetry breaking. Due to that origin we are less biased about hierarchies and discuss three different types of the inverse seesaw mechanism with different phenomenologies. We can successfully reproduce neutrino masses and mixing and our model is consistent with current bounds on neutrinoless double beta decay, non-unitarity of the PMNS matrix and charged lepton flavor violation.

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arXiv2017

Higgs boson pair productions in the Georgi-Machacek model at the LHC

Higgs bosons pair production is well known for its sensitivity to probing the sign and size of Higgs boson self coupling, providing a way to determine whether there is an extended Higgs sector. The Georgi-Machacek (GM) model extends the Standard Model (SM) with an $SU(2)_L$ triplet scalar field that has one real and one complex components. The Higgs self coupling now has a wider range than that in the SM, with even the possibility of a sign flip. The new heavy singlet Higgs boson $H^{0}_{1}$ can contribute to s-channel production of the $hh$ pairs. In this work, we study non-resonant/resonant Higgs boson pair productions $p p \rightarrow hh$ and $p p \rightarrow H^{0}_{1} \rightarrow hh$, focusing exclusively on the contribution of $H^0_1$. We show the sensitivity for Higgs boson pair production searches at the 13-TeV LHC with the luminosities of $3.2,\ 30$ and $100$~fb$^{-1}$.

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arXiv2017

Entangling Higgs production associated with a single top and a top-quark pair in the presence of anomalous top-Yukawa coupling

The ATLAS and CMS collaborations observed a mild excess in the associated Higgs production with a top-quark pair ($t\bar t h$) and reported the signal strengths of $ μ_{tth}^{\rm ATLAS}=1.81\pm 0.80$ and $μ_{tth}^{\rm CMS}=2.75\pm 0.99 $ based on the data collected at $\sqrt{s}$= 7 and 8 TeV. Although, at the current stage, there is no obvious indication whether the excess is real or due to statistical fluctuations, here we perform a case study of this mild excess by exploiting the strong entanglement between the associated Higgs production with a single top quark ($thX$) and $t\bar t h$ production in the presence of anomalous top-Yukawa coupling. As well known, $t\bar t h$ production only depends on the absolute value of the top-Yukawa coupling. Meanwhile, in $thX$ production, this degeneracy is lifted through the strong interference between the two main contributions which are proportional to the top-Yukawa and the gauge-Higgs couplings, respectively. Especially, when the relative sign of the top-Yukawa coupling with respect to the gauge-Higgs coupling is reversed, the $thX$ cross section can be enhanced by more than one order of magnitude. We perform a detailed study of the influence of $thX$ production on $t\bar{t}h $ production in the presence of the anomalous top-Yukawa coupling and point out that it is crucial to include $thX$ production in the analysis of the $t\bar t h$ data to pin down the sign and the size of the top-Yukawa coupling in future. While assuming the Standard Model (SM) value for the gauge-Higgs coupling, we vary the top-Yukawa coupling within the range allowed by the current LHC Higgs data. We consider the Higgs decay modes into multileptons, $b\bar b$ and $γγ$ putting a particular emphasis on the same sign dilepton events. We also discuss ...

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arXiv2017

Detecting multimuon jets from the Higgs exotic decays in the Higgs portal framework

A muon jet ($μ$-jet) is a very special feature that consists of a cluster of collimated muons from the decay of a fast moving light particle of mass about $\mathcal{O}$(1 GeV). We will use this feature to search for very light particles from rare decays of the Higgs boson. For such a small angular separation of muons which might come from a long-lived particle, both ATLAS and CMS could have the displaced-vertexing-reconstruction capability. We use two simple models of the Higgs-portal type to explore the possibilities of event topologies with two $2μ$-jets, one $2μ$-jet $\&$ one $4μ$-jet, and two $4μ$-jets in the final state at LHC-14. We also summarize existing constraints on these models.

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arXiv2016

Interpreting the 750 GeV Di-photon Resonance using photon-jets in Hidden-Valley-like models

Motivated by the di-photon resonance recently reported by the ATLAS and CMS collaborations at $\sqrt{s} =13$ TeV, we interpret the resonance as a scalar boson $X (750)$ in hidden-valley-like models. The scalar boson $X$ can mix with the standard model Higgs boson and thus can be produced via gluon fusion. It then decays into a pair of very light hidden particles $Y$ of sub-GeV, each of which in turn decays to a pair of collimated $ π^{0} $'s, and these two $ π^{0} $'s decay into photons which then form photon-jets. A photon-jet ($ γ$-jet) is a special feature that consists of a cluster of collinear photons from the decay of a fast moving light particle (sub-GeV). Because these photons inside the photon-jet are so collimated that it cannot be distinguished from a single photon, and so in the final state of the decay of $X(750)$ a pair of photon-jets look like a pair of single photons, which the experimentalists observed and formed the 750 GeV di-photon resonance. Prospects for the LHC Run-2 about other new and testable features are also discussed.

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arXiv2015

An Exploratory study of Higgs-boson pair production

Higgs-boson pair production is well known being capable to probe the trilinear self-coupling of the Higgs boson, which is one of the important ingredients of the Higgs sector itself. Pair production then depends on the top-quark Yukawa coupling $g_t^{S,P}$, Higgs trilinear coupling $λ_{3H}$, and a possible dim-5 contact-type $ttHH$ coupling $g_{tt}^{S,P}$, which may appear in some higher representations of the Higgs sector. We take into account the possibility that the top-Yukawa and the $ttHH$ couplings involved can be CP violating. We calculate the cross sections and the interference terms as coefficients of the square or the 4th power of each coupling $(g_t^{S,P}, λ_{3H}, g_{tt}^{S,P})$ at various stages of cuts, such that the desired cross section under various cuts can be obtained by simply inputing the couplings. We employ the $H H \to γγb \bar b$ decay mode of the Higgs-boson pair to investigate the possibility of disentangle the triangle diagram from the box digram so as to have a clean probe of the trilinear coupling at the LHC. We found that the angular separation between the $b$ and $\bar b$ and that between the two photons is useful. We obtain the sensitivity reach of each pair of couplings at the 14 TeV LHC and the future 100 TeV pp machine. Finally, we also comment on using the $b\bar b τ^+ τ^-$ decay mode in Appendix.

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arXiv2014

Probing the Top-Yukawa Coupling in Associated Higgs production with a Single Top Quark

Associated production of the Higgs boson with a single top quark proceeds through Feynman diagrams, which are either proportional to the hWW, top-Yukawa, or the bottom-Yukawa couplings. It was shown in literature that the interference between the top-Yukawa and the gauge-Higgs diagrams can be significant, and thus the measurement of the cross sections can help pin down the sign and the size of the top-Yukawa coupling. Here we perform a detailed study with full detector simulations of such a possibility at the LHC-14 within the current allowed range of hWW and top-Yukawa couplings, using h-> b b-bar, γγ, τ+ τ-, ZZ* -> 4 l modes. We found that the LHC-14 has the potential to distinguish the size and the sign of the top-Yukawa coupling. Among the channels the h-> b b-bar mode mode provides the best chance to probe the signal, followed by the h -> γγ mode, which has the advantage of a narrow reconstructed mass peak. We also pointed out that the spatial separation among the final-state particles has the potential in differentiating among various values of the top-Yukawa coupling.

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arXiv2013

WW Scattering in the Era of Post Higgs Discovery

More evidences have now been collected at the Large Hadron Collider suggesting the new 125 - 126 GeV boson is likely the long sought Higgs boson in the standard model. One pressing question continued being asked by theorists is whether this Higgs boson is a lone player responsible for the full electroweak symmetry breaking. Current data still allow room for additional Higgs bosons or some other UV physics that may play a partial role in electroweak symmetry breaking as well. We use the WW scattering to investigate such a possibility, using the two-Higgs-doublet model as a prototype. The WW scattering becomes strong when the extra Higgs bosons are very heavy. We study the sensitivity of the partially strong WW scattering signals at the 13 TeV Large Hadron Collider.

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arXiv2013

Implications on the Heavy CP-even Higgs Boson from Current Higgs Data

The current Large Hadron Collider data indicates that the newly observed resonance has the WW and ZZ modes consistent with the standard model Higgs boson, while the γγmode is about 1.2 - 2 times that of the standard model prediction and the tau-pair mode is suppressed. If this pattern persists in the upcoming data, it would be a sign for physics beyond the standard model. In the type II two-Higgs-doublet model, it is the region where \sinα\approx 0 and a moderately large \tanβ= 10 - 20 that the lighter CP-even Higgs boson can accommodate the current data. We note that in this region the heavier CP-even Higgs boson must have a large decay branching ratio into tau pairs. We find that this heavier Higgs boson can be observable in the associated production with a b\bar b pair and through the decay into a tau pair.

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arXiv2012

Various Models Mimicking the SM Higgs Boson

This review is based on the talk presented at the SUSY 2012 (Beijing). The new particle around 125 GeV observed at the Large Hadron Collider (LHC) is almost consistent with the standard model Higgs boson, except that the diphoton decay mode may be excessive. We summarize a number of possibilities. While at the LHC the dominant production mechanism for the Higgs boson of the standard model and some other extensions is via the gluon fusion process, the alternative vector-boson fusion is more sensitive to electroweak symmetry breaking. Using the well known dijet-tagging technique to single out the vector-boson fusion mechanism, we investigate potential of vector-boson fusion to discriminate a number of models suggested to give an enhanced inclusive diphoton production rate.

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