We study the possibility of discovering neutral scalar Higgs bosons in the $U(1)'$-extended supersymmetric standard model (USSM) at the CERN Large Hadron Collider (LHC), by examining their productions via the exotic quark loop in the gluon fusion process at leading order. It is possible in some parameter region that the neutral scalar Higgs bosons may have stronger couplings with the exotic quarks than with top quark. In this case, the exotic quarks may contribute more significantly than top quark in productions of the neutral scalar Higgs bosons in the gluon fusion process. We find that there is indeed some parameter region in the USSM that supports our speculations.
Flavour changing neutral scalar interactions are a standard feature of generic multi Higgs models. These are constrained by mixing in the neutral meson systems. We consider situations where there are natural cancellations in such contributions. In particular, when the spin 0 particle has both scalar and pseudoscalar couplings, one may have a self-cancellation. We illustrate one such partial cancellation with BGL models. We also inquire whether the flavour changing quark interactions can lead to new production mechanisms for a neutral scalar at LHC.
We consider the experimental data on neutral Kstar-meson production on nucleon and nuclear targets. The Quark-Gluon String Model quantitatively describes the inclusive density in the midrapidity region, as well as the initial energy and A dependences of the produced Kstar-mesons.
Single top production associated with a neutral scalar at LHC in topcolor-assisted technicolor
顶色辅助的人工色（TC 2）模型预测了一些中性标量，如顶介子（$π^0_t$）和顶希格斯（$h^0_t$）。这些标量具有变味中性流（FCNC）顶夸克耦合，其中顶粲跃迁耦合可能相当大。在欧洲核子研究中心的大型强子对撞机（LHC）上，这种FCNC耦合通过部分子过程$cg \to t π_t^0$和$cg \to t h_t^0$诱导了与中性标量相关的单顶产生。在本文中，我们研究了这些生产，发现它们的生产率可以超过$3σ$的LHC的参数空间的大部分灵敏度。由于在标准模型和最小超对称模型中，这些稀有过程在LHC中的产生率小得不可观测，因此这些稀有过程将作为TC2模型的一个很好的探针。
The inclusion of heavy neutral leptons to the Standard Model particle content could provide solutions to many open questions in particle physics and cosmology. The modification of the charged and neutral currents from active-sterile mixing of neutral leptons can provide novel signatures in Standard Model processes. We revisit the displaced vertex signature that could occur in collisions at the LHC via the decay of heavy neutral leptons with masses of a few GeV emphasizing the implications of flavor, kinematics, inclusive production and number of these extra neutral fermions. We study in partic…
Long-lived light particles (LLLPs) appear in many extensions of the standard model. LLLPs are usually motivated by the observed small neutrino masses, by dark matter or both. Typical examples for fermionic LLLPs (a.k.a. heavy neutral fermions, HNFs) are sterile neutrinos or the lightest neutralino in R-parity violating supersymmetry. The high luminosity LHC is expected to deliver up to 3/ab of data. Searches for LLLPs in dedicated experiments at the LHC could then probe the parameter space of LLLP models with unprecedented sensitivity. Here, we compare the prospects of several recent experimen…
We explore possible signatures for heavy neutrinos and neutral gauge boson, Z', in TeV scale B-L extension of the Standard Model (BLSM) with inverse seesaw mechanisms at the Large Hadron Collider. We show that due to new decay channels of Z' into heavy/inert neutrinos, the LHC stringent bounds imposed on Z' mass can be significantly relaxed. We analyze the pair production of heavy neutrinos decaying to four leptons plus two neutrinos, four jets plus two leptons, or three leptons plus two jets and one neutrino. We show that the 4l + 2 nu is the most promising decay channel for probing both Z' a…
The phenomenology of the neutral scalar bosons in the compact 341 model is discussed. We show that the predictions of this model are fairly good and compatible with the experimental data by calculating the signal strength of $h_1$ for the channels $b\bar{b}$, W$W^{*}$, Z$Z^{*}$, $τ\barτ$ and $γγ$. Moreover, we use the branching ratios to search for the heavy neutral scalar bosons $h_2$ and $h_3$ where we take into account the theoretical constraints to precise the allowed ranges for the fundamental parameters of the scalar potential.
We investigate long-lived particles (LLPs) produced in pair from neutral currents and decaying into a displaced electron plus two jets at the LHC, utilizing the proposed minimum ionizing particle timing detector at CMS. We study two benchmark models: the R-parity-violating supersymmetry with the lightest neutralinos being the lightest supersymmetric particle and two different $U(1)$ extensions of the standard model with heavy neutral leptons (HNLs). The light neutralinos are produced from the standard model $Z$-boson decays via small Higgsino components, and the HNLs arise from decays of a hea…
Heavy Neutral Leptons are naturally present in many well-motivated extensions of the Standard Model. If their mass is of few dozens of GeVs, they can be long-lived and lead to events with displaced vertices, giving rise to promising signatures due to the low background. We revisit the opportunities offered by the LHC to discover these long-lived states via searches with displaced vertices. We study in particular the implication on the parameter space sensitivity when all mixings to active flavors are taken into account.
Non-universal gaugino mass models can naturally account for the dark matter relic density via the bulk annihilation process with relatively light bino LSP and right sleptons in the mass range of ~ 100 GeV, while accommodating the observed Higgs boson mass of ~ 125 GeV with TeV scale squark/gluino masses. A class of these models can also account for the observed muon g-2 anomaly via SUSY loops with wino and left sleptons in the mass range of 400 -- 700 GeV. These models can be tested at LHC via electroweak production of charged and neutral wino pair, leading to robust trilepton and same sign di…
In this manuscript, we study the LHC signatures of a non-standard heavy neutral Higgs boson H at the 14 TeV LHC model-independently by taking the anomalous HVV coupling constants in the possible range obtained in our previous paper, Ref.[1]. We suggest WW scattering and VH associated production as two sensitive processes for detecting H, and the latter is more sensitive than the former. The study is at the hadron level with signals and backgrounds carefully calculated. Certain kinematic cuts are proposed to suppress the backgrounds effectively. We take several values of the heavy Higgs masses …
Heavy neutral leptons are present in many well-motivated beyond the Standard Model theories, sometimes being accessible at present colliders. Depending on their masses and couplings they could be long-lived and lead to events with displaced vertices, and thus to promising signatures due to low Standard Model background. We revisit the potential of the LHC to discover this kind of new particles via searches for displaced vertices, which can probe masses of few GeV for mixings currently allowed by experimental constraints. We also discuss the importance of considering all the possible production…
LHC Detection of Neutral MSSM Higgs Bosons via $gg\rta b\anti b \h\rta b\anti b b\anti b$
我们证明，同时检测的两个中性希格斯玻色子的最小超对称模型将有可能在大型强子对撞机在$b\anti b b\anti b$的最终状态，提供$\tanb$是大的和$b$标记可以进行良好的效率和纯度。这种模式增强了已经建立的保证，即不存在超对称参数空间的区域，在该区域中，在LHC上可以看到该模型的希格斯玻色子玻色子。
The anomalous neutral triple gauge boson couplings (aNTGCs) for the Z gamma gamma and Z gamma Z vertices described by dimension-eight operators are examined through the process pp to l^{+}l^{-} gamma at the High-Luminosity Large Hadron Collider (HL-LHC). We performed an analysis on transverse momentum of photon and angular distribution of charged lepton in the final state including detector effects. Sensitivity limits of the C_{\widetilde{B}W}, C_{BB} couplings are obtained at 95 % C.L. to constrain for the range [-1.88: 1.88] TeV^{-4}, [-1.47: 1.47] TeV^{-4} and [-1.14:1.14] TeV^{-4}, [-0.86:…
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-luminos…
Neutral $Z$ boson pair production due to radion resonance in the Randall-Sundrum model: prospects at the CERN LHC
在大型强子对撞机（LHC）上，由于Radion共振而产生的中性$Z$玻色子对是探索扭曲几何（Randall-Sundrum模型）概念的一个有趣过程。由于迹线异常和顶（夸克）环增强了镭子与一对胶子的耦合，镭子可以提供比任何新物理效应更大的事件率可能性。使用适当的放射性顶-反顶（夸克离壳）耦合，我们得到了正确的Radion生产率在大型强子对撞机和探索的几个特点，较重的Radion衰变成一对真正的$Z$玻色子，随后衰变成带电的$4 l (l=e, μ)$轻子（镀金模式）。使用信号和背景事件率，我们得到了在$5σ$，$10σ$发现水平上的Radion质量$m_ϕ$和Radion vev $\vphi$的界限。
After the discovery of a Standard Model-like boson with mass of about 125 GeV the possibility of an enlarged scalar sector arises naturally. Here we present the current status of the phenomenology of the two-Higgs-doublet models with a special focus on the charged Higgs sector. If one considers a fermiophobic charged Higgs (it does not couple to fermions at tree level), all present experimental bounds are evaded trivially, therefore one needs to consider other decay and production channels. In this work we also present some of the interesting features of this specific scenario.
In this paper, the top quark pair production events are analyzed as a source of neutral Higgs bosons of two Higgs doublet model type I at LHC. The production mechanism is $pp \to H/A \to t\bar{t}$ assuming a fully hadronic final state through $t \to Wb \to jjb$. In order to distinguish the signal from the main background which is the standard model $t\bar{t}$, we benefit from the fact that the top quarks in signal events acquire a large Lorentz boost due to the heavy neutral Higgs boson. This feature leads to three collinear jets (a fat jet) which is a discriminating tool for identification of…
Single top quark production is a powerful process to search for new physics signs. In this work we propose and investigate a search for top quark flavor changing neutral currents (FCNC) via a photon using direct single top quark production events in proton-proton collisions at the LHC at CERN. We show that the direct single top quark final state can provide constraints on the strengths of tq$γ$ (top-quark-$γ$) and tqg (top-quark-gluon) FCNC couplings simultaneously. Results of a search for direct single top quark production at the LHC at a center-of-mass energy of 8 TeV performed by the ATLAS …
In supersymmetry (SUSY) models with low electroweak naturalness (natSUSY), which have been suggested to be the most likely version of SUSY to emerge from the string landscape, higgsinos are expected at the few hundred GeV scale whilst electroweak gauginos inhabit the TeV scale. For TeV-scale heavy neutral SUSY Higgs bosons H and A, as currently required by LHC searches, then the dominant decay modes of H, A are into gaugino plus higgsino provided these decays are kinematically open. The light higgsinos decay to soft particles so are largely invisible whilst the gauginos decay to W, Z or h plus…
This is a sequel to our previous work on LHC phenomenology of the type II seesaw model in the nondegenerate case. In this work, we further study the pair and associated production of the neutral scalars H^0/A^0. We restrict ourselves to the so-called negative scenario characterized by the mass order M_{H^{\pm\pm}}>M_{H^\pm}>M_{H^0/A^0}, in which the H^0/A^0 production receives significant enhancement from cascade decays of the charged scalars H^{\pm\pm},~H^\pm. We consider three important signal channels---b\bar{b}γγ, b\bar{b}τ^+τ^-, $b\bar{b}\ell^+\ell^-\cancel{E}_T$---and perform detailed si…
In this paper we show that the diphoton mass spectrum in proton-proton collisions at the LHC is sensitive to the top quark flavor changing neutral current in the vertices of $tuγ$ and $tcγ$. The diphoton mass spectrum measured by the CMS experiment at the LHC at a center-of-mass energy of 8 TeV and an integrated luminosity of 19.5 fb$^{-1}$ is used as an example to set limits on these FCNC couplings. It is also shown that the angular distribution of the diphotons is sensitive to anomalous $tuγ$ and $tcγ$ couplings and it is a powerful tool to probe any value of the branching fraction of top qu…
Searches at the Large Hadron Collider (LHC) for neutral, long-lived particles have historically relied on the detection of displaced particles produced by their decay $\textit{within}$ the detector volume. In this paper we study the potential of the complementary signature comprising of the missing transverse energy ($E_T^{miss}$) signal, traditionally used to look for dark matter, e.g., the lightest supersymmetric particle (LSP), to extend the LHC coverage to models with long-lived (LL) particles when they decay $\textit{outside}$ the detector. Using CMS and ATLAS analyses at the 8 TeV LHC, w…
Direct Chargino-Neutralino Production at the LHC: Interpreting the Exclusion Limits in the Complex MSSM
我们重新评估的排斥限制的参数描述的超对称（SUSY）电弱部门的MSSM从寻找直接chargino中性伴子生产在大型强子对撞机。我们从简化模型中获得的已发表的极限开始，其中对于重slepton的情况，相关的分支比BR（neu 2-> neu 1 Z）被设置为1。我们展示了如何衰减模式neu 2-> neu 1 h，这不能被忽视，在任何现实的模型，一旦运动学允许，大大减少了排除的参数区域。我们分析了排斥区对高更诺软超对称性破缺质量参数M_1的相位、对轻标量τ的质量、对tb以及对夸克和斯莱普顿质量尺度的依赖性。在所有设想方案中，都可以观察到被排除的参数范围大幅缩小。使用复杂MSSM的完整NLO计算来评估电荷伴子和中性伴子的分支比。研究了非线性光学计算对不相容边界影响的大小。我们还评估了收集100/fb后，在运行在13 TeV的大型强子对撞机的实验分析的潜在影响。
We consider relatively rare events of SUSY production at the LHC without missing $p_T$. Namely, we discuss the chargino production with further decay into the W-boson and the neutralino when the masses of chargino and neutralino differ by 80-90 GeV. In this case, in the final state one has two Ws and missing $E_T$ but no missing $P_T$. The produced neutralinos are just busted along Ws. Within the MSSM such events are quite probable in the region of parameter space close to the EWSB border line. The excess in the W production cross-section may achieve a few \%.
New massive resonances are predicted in many extensions to the Standard Model (SM) of particle physics and constitutes one of the most promising searches for new physics at the LHC. We present a feasibility study to search for new heavy neutral gauge bosons using vector boson fusion (VBF) processes, which become especially important as the LHC probes higher collision energies. In particular, we consider the possibility that the discovery of a $Z'$ boson may have eluded searches at the LHC. The coupling of the $Z'$ boson to the SM quarks can be small, and thus the $Z'$ would not be discoverable…
