arXiv subjects

Jinmian Li

Publications and source records attributed to Jinmian Li.

At least 55 records · Page 3Linked to original sources

arXiv2018

Impact of the 125 GeV Higgs boson on the singlet fermion dark matter searches at the LHC

The search for singlet fermion dark matter at high-energy colliders is commonly analyzed with a singlet scalar mediator, which however violates the standard model (SM) gauge invariance, renormalizability and unitarity. These problems can be cured by introducing a mixing between the singlet scalar $s$ and the SM Higgs boson $h$. Thus one has to consider two scalar mediators $h_1$ and $h_2$, where $h_1$ is identified as the discovered 125 GeV Higgs boson. As a specific example, we consider the dark matter (DM) search in the $t \bar{t} + E_{T}^{\text{miss}}$ channel. According to the masses of dark matter and two scalar mediators, we classify the process into four cases. By investigating the total cross sections and differential distributions, we find that the contribution of the 125~GeV Higgs boson $h_1$ cannot be neglected in all cases and can even dominate once $h_1$ is on-shell in dark matter production. Further, we study the impact of $h_1$ on the LHC bounds of dark matter searches in the hadronic and semileptonic channels with the integrated luminosity of $36~\text{fb}^{-1}$. Finally we make a brief comment that $h_1$ should be also considered in the vector DM search at high-energy colliders.

hep-ph↗

arXiv2018

Prospects for discovery and spin discrimination of dark matter in Higgs portal DM models and their extensions at 100 TeV $pp$ collider

We study the discovery and discriminating prospects of the Higgs portal dark matter (DM) models for scalar, fermion and vector DM and their extensions in proton-proton ($pp$) collisions. The $t\bar{t}+$DM associated production in dileptonic final states is considered, in which the stransverse mass of two leptons is found to be effective in suppressing the Standard Model backgrounds along with the missing transverse energy and the angle between two leptons. The distributions of missing transverse energy and polar angle between two leptons are used for a discrimination of the spin nature of DM. For the proposed benchmark points, the discovery/exclusion can be made with an integrated luminosity less than 1 ab$^{-1}$ given a 1\% systematic uncertainty, while the spin discrimination require integrated luminosity of a few O(10) ab$^{-1}$ given a 0.5\% systematic uncertainty. The DM phenomenology is also discussed. A consistent DM candidate can be obtained either by extending our model where the Higgs portal couples to excited dark states that decay into DM, or modifying the coupling form into pseudoscalar.

hep-ph↗

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.

hep-ph↗

arXiv2018

Central-edge asymmetry as a probe of Higgs-top coupling in $t\bar{t}h$ production at LHC

The Higgs-top coupling plays a central role in the hierarchy problem and the vacuum stability of the Standard Model (SM). We propose a central-edge asymmetry ($A_{CE}$) to probe the CP violating Higgs-top coupling in dileptonic channel of $t\bar{t}h(\to b\bar{b})$ production at the LHC. We demonstrate that the CP-violating Higgs-top coupling can affect the central-edge asymmetry through distorting $Δy_{\ell^+\ell^-}$ distribution because of the contribution of new top charge asymmetric term. Since $Δy_{\ell^+\ell^-}$ distribution is frame-independent and has a good discrimination even in boosted regime, we use the jet substructure technique to enhance the observability of the dileptonic channel of $t\bar{t}h$ production. We find that (1) the significance of dileptonic channel of $t\bar{t}h$ production can reach $5σ$ for CP phase $ξ=0,π/4,π/2$ when the luminosity ${\cal L}=795,993,1276$ fb$^{-1}$ at 14 TeV LHC. (2) the central-edge asymmetry $A_{CE}$ show a good discrimination power of CP phase of $t\bar{t}h$ interaction, which are -40.26\%, -26.60\%, -9.47\% for $ξ=0$, $π/4$, $ π/2$ respectively and are hardly affected by the event selections. Besides, by performing the binned-$χ^2$ analysis of $Δy_{\ell^+\ell^-}$ distribution, we find that the scalar and pseudo-scalar interactions can be distinguished at 95\% C.L. level at 14 TeV HL-LHC.

hep-ph↗

arXiv2017

Characterizing Higgs portal dark matter models at the ILC

We study the Dark Matter (DM) discovery prospect and its spin discrimination in the theoretical framework of gauge invariant and renormalizable Higgs portal DM models at the ILC with $\sqrt{s} = 500$ GeV. In such models, the DM pair is produced in association with a $Z$ boson. In case the singlet scalar DM, the mediator is just the SM Higgs boson, whereas for the fermion or vector DM there is an additional singlet scalar mediator that mixes with the SM Higgs boson, which produces significant observable differences. After careful investigation of the signal and backgrounds both at parton level and at detector level, we find the signal with hadronically decaying $Z$ boson provides a better search sensitivity than the signal with leptonically decaying $Z$ boson. Taking the fermion DM model as a benchmark scenario, when the DM-mediator coupling $g_χ$ is relatively small, the DM signals are discoverable only for benchmark points with relatively light scalar mediator $H_2$. And the spin discriminating from scalar DM is always promising while it is difficult to discriminate from vector DM. As for $g_χ$ approaching the perturbative limit, benchmark points with the mediator $H_2$ in the full mass region of interest are discoverable. And the spin discriminating from both the scalar and fermion DM are quite promising.

hep-ph↗

arXiv2017

Asymmetric Dark Matter Bound State

We propose an interesting framework for asymmetric scalar dark matter (ADM), which has novel collider phenomenology in terms of an unstable ADM bound state (ADMonium) produced via Higgs portals. ADMonium is a natural consequence of the basic features of ADM: the (complex scalar) ADM is charged under a dark local $U(1)_d$ symmetry which is broken at a low scale and provides a light gauge boson $X$. The dark gauge coupling is strong and then ADM can annihilate away into $X$-pair effectively. Therefore, the ADM can form bound state due to its large self-interaction via $X$ mediation. To explore the collider signature of ADMonium, we propose that ADM has a two-Higgs doublet portal. The ADMonium can have a sizable mixing with the heavier Higgs boson, which admits a large cross section of ADMonium production associated with $b\bar b$. The resulting signature at the LHC depends on the decays of $X$. In this paper we consider a case of particular interest: $pp\ra b\bar b+ {\rm ADMonium}$ followed by ${\rm ADMonium}\ra 2X\ra 2e^+e^-$ where the electrons are identified as (un)converted photons. It may provide a competitive explanation to heavy di-photon resonance searches at the LHC.

hep-ph↗

arXiv2017

Uncover Compressed Supersymmetry via Boosted Bosons from the Heavier Stop/Sbottom

A light stop around the weak scale is a hopeful messenger of natural supersymmetry (SUSY), but it has not shown up at the current stage of LHC. Such a situation raises the question of the fate of natural SUSY. Actually, a relatively light stop can easily be hidden in a compressed spectra such as mild mass degeneracy between stop and neutralino plus top quark. Searching for such a stop at the LHC is a challenge. On the other hand, in terms of the argument of natural SUSY, other members in the stop sector, including a heavier stop $\tilde{t}_2$ and lighter sbottom $\tilde{b}_1$ (both assumed to be left-handed-like), are also supposed to be relatively light and therefore searching for them would provide an alternative method to probe natural SUSY with a compressed spectrum. In this paper we consider quasi-natural SUSY which tolerates relatively heavy colored partners near the TeV scale, with a moderately large mass gap between the heavier members and the lightest stop. Then $W/Z/h$ as companions of $\tilde{t}_2$ and $\tilde{b}_1$ decaying into $\tilde{t}_1$ generically are well boosted, and they, along with other visible particles from $\tilde{t}_1$ decay, are a good probe to study compressed SUSY. We find that the resulting search strategy with boosted bosons can have better sensitivity than those utilizing multi-leptons.

hep-ph↗

arXiv2017

Minimal renormalizable simplified dark matter model with a pseudoscalar mediator

We consider a minimal renormalizable and gauge invariant dark matter (DM) model, in which the singlet fermion DM has only axial couplings to a new pseudoscalar mediator. The mixing between the pseudoscalar mediator and the standard model (SM) Higgs boson induces the interactions between the DM and SM particles. The DM candidate in this model can provide the correct thermal relic density and evades all direct detections, while it can produce observable signals in indirect detection experiments due to its large annihilation cross section. A comparative study for DM phenomenology at the LHC is conducted for models with scalar mediators that have either scalar or pseudoscalar couplings to SM particles and the DM. We find that the three scenarios have distinguishable features in scalar decay branching ratio, DM pair production cross section as well as the signal reaches at the LHC. The LHC searches for some visible signals related to the scalar sector are also discussed.

hep-ph↗

arXiv2017

Implication of the ALEPH 30 GeV dimuon resonance at the LHC

Recent reanalysis of ALEPH data on Z -> b bar{b} + X seems to indicate an existence of the dimuon excess around 30 GeV with a branching fraction for Z -> b bar{b} mu^+ mu^- around 1.1 X 10^{-5}. In this letter, we discuss three different types of simplified models for this possible excess. In the first class of models, we assume a new resonance couples to both b bar{b} and mu^+ mu^-. Within the allowed parameter space for the ALEPH data, this type of models is excluded because of too large Drell-Yan production of dimuon from the b bar{b} collision at the LHC. In the second model, we assume that the 30 GeV excess is a new gauge boson Z' that couples to the SM b and a new vectorlike singlet B quark heavier than Z and not to b bar{b}. Then one can account for the ALEPH data without conflict with the DY constraint. The new vectorlike quark B can be pair produced at the LHC 8/13 TeV by QCD with sigma(BB) ~ O(100-1000) pb, and Bq production rate is sigma(Bq) ~ a few pb which is larger than sigma(Bb) roughly by an order of magnitude. Their signatures at the LHC would be 2b + 4mu, bj + 2mu and 2b + 2mu, respectively, which however might have been excluded already by LHC run I and II data since the multi-muon events have low SM background and are rare at the LHC. In the third model, we consider Z -> Z' phi followed by Z' -> mu^+ mu^- and phi -> b bar{b} assuming that the Higgs field for Z' mass is also charged under the SM U(1)_Y gauge symmetry. In this class of model, we could accommodate the Br(Z -> b bar{b} mu^+ mu^-) ~ 1.1 X 10^{-5} if we assume very large U(1)' charge for the U(1)' breaking Higgs field. Finally, we study various kinematic distributions of muons and b jets in all the three models, and find that none of the models we consider in this paper are not compatible with the kinematic distributions extracted from the ALEPH data.

hep-ph↗

arXiv2017

Missing particle associated with two bottom quarks at the LHC: Mono-$b$ versus 2$b$ with razor variables

The extended Higgs sector, such as by a second Higgs doublet of type-II, provides portals to dark sector which contains missing particles at the LHC, e.g., dark matter (DM) particles. In this paper, working in the simplified model and taking into consideration the wide decay width effect of the mediator, we analyze the characteristic signatures of mono-$b$+MET and 2$b$+MET at the LHC. The latter signature was believed to be ineffective, while we found that, with the aid of razor shape analysis, it should be as important as the mono-$b$ signature. In the region of relatively low mediator mass (below a few hundred GeV), by requiring the signal to background ratio greater than a few percent, the 2$b$-tagged razor analysis has comparable sensitivity to the mono-$b$ search; it is even better for mediator lighter than $\sim 200$ GeV.

hep-ph↗

arXiv2016

Interference effects of two scalar boson propagators on the LHC search for the singlet fermion DM

A gauge invariant UV-completion for singlet fermion DM interacting with the standard model (SM) particles involves a new singlet scalar. Therefore the model contains two scalar mediators, mixtures of the SM Higgs boson and a singlet scalar boson. Collider phenomenology of the interference effect between these two scalar propagators is studied in this work. This interference effect can be either constructive or destructive in the DM production cross section depending on both singlet scalar and DM masses, and it will soften the final state jets in the full mass region. Applying the CMS mono-jet search to our model, we find the interference effect plays a very important role in the DM search sensitivity, and the DM production cross section of our model is more than one order of magnitude below the LHC sensitivity at current stage.

hep-ph↗

arXiv2016

Boosting the charged Higgs search prospects using jet substructure at the LHC

Charged Higgs bosons are predicted in variety of theoretically well-motivated new physics models with extended Higgs sectors. In this study, we focus on a type-II two Higgs doublet model (2HDM-II) and consider a heavy charged Higgs with its mass ranging from 500 GeV to 1 TeV as dictated by the $b\to sγ$ constraints which render $M_{H^\pm}>480$ GeV. We study the dominant production mode $H^\pm t$ associated production with $H^\pm \to W^\pm A$ being the dominant decay channel when the pseudoscalar $A$ is considerably lighter. For such a heavy charged Higgs, both the decay products $W^\pm$ and $A$ are relatively boosted. In such a scenario, we apply the jet substructure analysis of tagging the fat pseudoscalar and $W$ jets in order to eliminate the standard model background efficiently. We perform a detailed detector simulation for the signal and background processes at the 14 TeV LHC. We introduce various kinematical cuts to determine the signal significance for a number of benchmark points with charged Higgs boson mass from 500 GeV to 1 TeV in the $W^\pm A$ decay channel. Finally we perform a multivariate analysis utilizing a boosted decision tree algorithm to optimize these significances.

hep-ph↗

arXiv2016

Investigating light NMSSM pseudoscalar states with boosted ditau tagging

We study a class of realizations of the Next-to-Minimal Supersymmetric Standard Model that is motivated by dark matter and Higgs data, and in which the lightest pseudoscalar Higgs boson mass is smaller than twice the bottom quark mass and greater than twice the tau lepton mass. In such scenarios, the lightest pseudoscalar Higgs boson can be copiously produced at the LHC from the decay of heavier superpartners and will dominantly further decay into a pair of tau leptons that is generally boosted. We make use of a boosted object tagging technique designed to tag such a ditau jet, and estimate the sensitivity of the LHC to the considered supersymmetric scenarios with 20 to 50~fb$^{-1}$ of proton-proton collisions at a center-of-mass energy of 13~TeV.

hep-ph↗

arXiv2016

The Maximal $U(1)_L$ Inverse Seesaw from $d=5$ Operator and Oscillating Asymmetric Sneutrino Dark Matter

The maximal $U(1)_L$ supersymmetric inverse seesaw mechanism (M$L$SIS) provides a natural way to relate asymmetric dark matter (ADM) with neutrino physics. In this paper we point out that, M$L$SIS is a natural outcome if one dynamically realizes the inverse seesaw mechanism in the next-to minimal supersymmetric standard model (NMSSM) via the dimension-five operator $(N)^2S^2/M_*$, with $S$ the NMSSM singlet developing TeV scale VEV; it slightly violates lepton number due to the suppression by the fundamental scale $M_*$, thus preserving $U(1)_L$ maximally. The resulting sneutrino is a distinguishable ADM candidate, oscillating and favored to have weak scale mass. A fairly large annihilating cross section of such a heavy ADM is available due to the presence of singlet.

hep-ph↗

arXiv2016

LHC searches for heavy neutral Higgs bosons with a top jet substructure analysis

We study the LHC searches for the heavy $CP$-odd Higgs boson $A$ and $CP$-even Higgs boson $H$ in the context of general two-Higgs-doublet model. Specifically, we consider the decay mode of $A/H\to t \bar t $ through the $b \bar b$ or $t \bar t $ associated production channels. In the so-called "alignment limit" of the two-Higgs-doublet model, this decay mode can be the most dominant one. By employing the HEPTopTagger and the multi-variable-analysis method, we present the search sensitivities for both $CP$-odd Higgs boson $A$ and $CP$-even Higgs boson $H$ via these channels at the high-luminosity LHC runs.

hep-ph↗

arXiv2016

New Avenues to Heavy Right-handed Neutrinos with Pair Production at Hadronic Colliders

In many models incorporating the type-I seesaw mechanism, the right-handed neutrino ($N$) couples to heavy vector/scalar bosons and thereby has resonant pair production. It barely receives attention thus far, however, it may provide the best avenue to probe TeV scale $N$ without requiring anomalously large mixing between $N$ and the active neutrino $ν_L$. In this paper we explore the discovery prospects of (mainly heavy) $N$ pair production at the 14 TeV LHC and future 100 TeV $pp$ collider, based on the three signatures: 1) trilepton from $ N(\rightarrow \ell W_\ell)N(\rightarrow \ell W_h)$ with $W_{\ell/h}$ the leptonically/hadronically decaying $W$; 2) boosted di-Higgs boson plus MET from $N(\rightarrow ν_L h)N(\rightarrow ν_L h)$; 3) a single boosted Higgs with leptons and MET from $N(\rightarrow \ell W_\ell)N(\rightarrow ν_L h)$. At the 100 TeV collider, we also consider the situation when the Higgs boson is over boosted thus losing its jet substructure. Interpreting our tentative results in the benchmark model, the local $B-L$ model, we find that the (multi-) TeV scale $N$ can be probed at the (100) 14 TeV colliders.

hep-ph↗

arXiv2016

Gamma rays from muons from WIMPs: Implementation of radiative muon decays for dark matter analyses

Dark matter searches in gamma ray final states often make use of the fact that photons can be produced from final state muons. Modern Monte Carlo generators and DM codes include the effects of final state radiation from muons produced in the dark matter annihilation process itself, but neglect the O(1%) radiative correction that arises from the subsequent muon decay. After implementing this correction we demonstrate the effect that it can have on dark matter phenomenology by considering the case of dark matter annihilation to four muons via scalar mediator production. We first show that the AMS-02 positron excess can no longer easily be made consistent with this final state once the Fermi-LAT dwarf limits are calculated with the inclusion of radiative muon decays, and we next show that the Fermi-LAT galactic centre gamma excess can be improved with this final state after inclusion of the same effect. We provide code and tables for the implementation of this effect in the popular dark matter code micrOMEGAs, providing a solution for any model producing final state muons.

hep-ph↗

arXiv2016

New Physics Opportunities in the Boosted Di-Higgs plus \ET Signature

The Higgs field in the standard model (SM) may couple to new physics sectors related with dark matter and/or massive neutrinos. In this paper we propose a novel signature, the boosted di-Higgs boson plus \ET (which is either a dark matter or neutrino), to probe those new physics sectors. In a large class of models, in particular the supersymmetric SMs and low scale seesaw mechanisms, this signature can play a key role. The signature has clear background, and at the $\sqrt s=$14 TeV high luminosity (HL-)LHC, we can probe it with production rate as low as $\sim$ 0.1 fb. We apply it to benchmark models, supersymmetry in the bino-Higgsino limit, the canonical seesaw model and little Higgs model, finding that masses of Higgsino, right-handed neutrino and heavy vector boson can be probed up to $\sim$ 500 GeV, 650 GeV and 900 GeV, respectively.

hep-ph↗