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$^{-1}$.
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 …
We show that the dominant channel proposed for the determination of the Higgs boson trilinear coupling, $pp\to HH+X$ via gluon fusion, exhibits an interference structure that is independent of the collider energy for collider energies in the range $8\,{\rm TeV}\leq \sqrt{s}\leq 100\,{\rm TeV}$ and is almost maximally destructive. This insensitivity to the collider energy remains approximately true for a variety of other two Higgs production mechanisms although the magnitude of the interference varies widely.
The possibility of generating a large trilinear $A_t$ soft supersymmetry breaking coupling at low energies through renormalisation group evolution in the 5D MSSM is investigated. Using the power law running in five dimensions and a compactification scale in the 10-$10^3$ TeV range, to show that gluino mass may drive a large enough $A_t$ to reproduce the measured Higgs mass and have a light stop superpartner below $\sim 1$ TeV as preferred by the fine tuning argument for the Higgs mass.
Non-zero trilinear parameter in the mSUGRA model - dark matter and collider signals at Tevatron and LHC
在具有小$m_0$和小$m_{1/2}$的最小超引力（mSUGRA）模型中，参数空间的现象学上可行和有趣的区域与WMAP关于暗物质遗迹密度的数据和LEP 2中最轻的希格斯标量$ m_h>$ 114 GeV的质量上的束缚一致，如果相当特别的假设$A_0$ =0，则打开，其中$A_0$是常见的三线性软破裂参数，在大多数现有的分析中使用的是放松的。由于该区域对应于相对较轻的方子和胶子，它们可能在LHC实验的早期阶段被广泛探测，因此详细研究了$A_0$的中等或大负值的后果。我们发现，在该区域，最轻超对称粒子对湮灭、超对称粒子对与较轻的τ-slepton（${\tilde τ}_1$）共湮灭和超对称粒子对与较轻的顶夸克（${\tilde t}_1$）共湮灭等过程对观测到的暗物质遗迹密度都有贡献. % \sout{The possibility that a relic density producing ${\tilde t}_1$ can be %observed at the current experiments at the Tevatron is wide open.}一个${\tilde t}_1$，可以参与共湮灭与最轻的中性伴子，以满足WMAP约束的遗迹密度，同时被观察到在目前的实验在Tevatron的可能性是很大的开放。在大型强子对撞机上，大量的夸克-胶子事件导致了一个非常独…
We study the impact of large trilinear R-parity violating couplings on the lightest CP-even Higgs boson mass in supersymmetric models. We use the publicly available computer codes SARAH and SPheno to compute the leading two-loop corrections. We use the effective potential approach. For not too heavy third generation squarks (< 1 TeV) and couplings close to the unitarity bound we find positive corrections up to a few GeV in the Higgs mass.
We present results for Higgs boson pair production with variations of the trilinear Higgs boson self-coupling at next-to-leading order (NLO) in QCD including the full top quark mass dependence. Differential results at 14 TeV are presented, and we discuss the implications of anomalous trilinear couplings as well as differences between the PYTHIA 8.2 and HERWIG 7.1 parton showers in combination with POWHEG. The implementation of the NLO QCD calculation with variable Higgs boson self-coupling is made publicly available in the POWHEG-BOX-V2 Monte Carlo framework. A simple method for using the new …
We propose the signal $1b+1l+N_j+\etslash$ along with appropriate selection criteria for the LHC 7 TeV run, where the number of jets $(N_j)$ is $\ge$ 2 or 4. These signals can complement the canonical $Jets + \etslash$ signature since they are sensitive to the trilinear soft breaking parameter $(A_0)$ and low values of the parameter tan$β$ in the minimal supergravity (mSUGRA) model. A large region of this mSUGRA parameter space within the reach of the ongoing experiments at the LHC is disfavoured by the bound on the lightest Higgs boson mass ($m_h \ge 114.4 $ GeV) unless $A_0$ has moderate to …
It has been argued that requiring low electroweak fine-tuning (EWFT) along with a (partial) decoupling solution to the SUSY flavor and CP problems leads to a sparticle mass spectra characterized by light Higgsinos at 100-300 GeV, sub-TeV third generation scalars, gluinos at a few TeV and multi-TeV first/second generation scalars (natural SUSY). We show that by starting with multi-TeV first/second and third generation scalars and trilinear soft breaking terms, the natural SUSY spectrum can be generated radiatively via renormalization group running effects. Using the complete 1-loop effective po…
Double Higgs production at TeV Colliders in the Minimal Supersymmetric Standard Model
在最小超对称标准模型（MSSM）中重建Higgs势需要测量三线性Higgs自耦合。“双希格斯粒子产生”小组一直在研究在大型强子对撞机和未来的线性对撞机上探测依赖这些顶点的过程特征的可能性。作为参考反应，我们分别选择了$gg\to hh$和$e^+e^-\to h h Z$，其中$h$是MSSM希格斯玻色子中最轻的。在这两种情况下，均涉及$Hhh$相互作用。对于$m_H>2m_h$，这两个反应在$H\to hh$模式下是共振的，提供了在两个加速器处都可检测的截面，并且对所涉及的三线性耦合的强度非常敏感。我们探讨这种质量制度的MSSM在$h\to b\bar b$衰变通道，也占不可约的背景效应。
An important physics goal of a possible next-generation high-energy hadron collider will be precision characterisation of the Higgs sector and electroweak symmetry breaking. A crucial part of understanding the nature of electroweak symmetry breaking is measuring the Higgs self-interactions. We study dihiggs production in proton-proton collisions at 100 TeV centre of mass energy in order to estimate the sensitivity such a machine would have to variations in the trilinear Higgs coupling around the Standard Model expectation. We focus on the two b-jets plus diphotons final state, including possib…
We perform a detailed study of double Higgs production via gluon fusion in the Effective Field Theory (EFT) framework where effects from new physics are parametrized by local operators. Our analysis provides a perspective broader than the one followed in most of the previous analyses, where this process was merely considered as a way to extract the Higgs trilinear coupling. We focus on the $hh \to b\bar bγγ$ channel and perform a thorough simulation of signal and background at the 14 TeV LHC and a future 100 TeV proton-proton collider. We make use of invariant mass distributions to enhance the…
In light of a discrepancy of the direct $CP$ violation in $K\toππ$ decays, $\varepsilon'/\varepsilon_K$, we investigate gluino contributions to the electroweak penguin, where flavor violations are induced by squark trilinear couplings. Top-Yukawa contributions to $ΔS = 2$ observables are taken into account, and vacuum stability conditions are evaluated in detail. It is found that this scenario can explain the discrepancy of $\varepsilon'/\varepsilon_K$ for the squark mass smaller than 5.6 TeV. We also show that the gluino contributions can amplify $\mathcal{B}(K \to πν\overlineν)$, $\mathcal{B…
We consider the ratio between the double and single Higgs production cross sections and examine the prospect of measuring the trilinear Higgs self-coupling using this observable. Such a ratio has a reduced theoretical (scale) uncertainty than the double Higgs cross section. We find that with 600/fb, the 14 TeV LHC can constraint the trilinear Higgs self coupling to be positive, and with 3000/fb one could measure it with a +30 % {-20 %}) accuracy.
In the presence of large extra dimensions, the fundamental scale could be as low as a few TeV. This yields leptogenesis and seesaw at a TeV scale. Phenomenologically two TeV-scale Majorana fermions with a small mass split can realize a resonant leptogenesis whereas a TeV-scale Higgs triplet with a small trilinear coupling to the standard model Higgs doublet can give a verifiable seesaw. We propose an interesting scenario where the small parameters for the resonant leptogenesis and the type-II seesaw can be simultaneously generated by the propagation of lepton number violation from distant bran…
We consider modifications of the Higgs potential due to new physics at high energy scales. These upset delicate cancellations predicted by the Standard Model for processes involving Higgs bosons and longitudinal gauge bosons, and lead to a breakdown of the theory at high energies. We focus on modifications of the Higgs trilinear coupling and use the violation of tree-level unitarity as an estimate of the scale where the theory breaks down. We obtain a completely model-independent bound of ~ 13 TeV for an order-1 modification of the trilinear. We argue that this bound can be saturated only in f…
We propose a method to determine the trilinear Higgs self coupling that is alternative to the direct measurement of Higgs pair production total cross sections and differential distributions. The method relies on the effects that electroweak loops featuring an anomalous trilinear coupling would imprint on single Higgs production at the LHC. We first calculate these contributions to all the phenomenologically relevant Higgs production ($gg{\rm F}$, VBF, $WH$, $ZH$, $t\bar tH$) and decay ($γγ$, $WW^{*}/ZZ^{*}\to 4f$, $b\bar b$, $ττ$) modes at the LHC and then estimate the sensitivity to the trili…
Neutral Higgs Boson Pair-Production and Trilinear Self-Couplings in the MSSM at ILC and CLIC Energies
我们在未来国际线性$e^{+}e^{-}$对撞机（ILC）和紧凑型线性对撞机（CLIC）上研究了最小超对称标准模型（MSSM）中性希格斯玻色子的成对产生和三重自耦合。该分析基于$e^{+}e^{-}\to b \bar b h_ih_i, t \bar t h_ih_i$与$h_i=h, H, A$的反应。我们评估了$b\bar bh_ih_i$，$t\bar th_ih_i$的总截面，并计算了事件的总数，考虑在树级的费曼图的完整集合。我们在$κ=-1$和+2范围内改变三重耦合$κλ_{hhh}$、$κλ_{Hhh}$、$κλ_{hAA}$、$κλ_{HAA}$、$κλ_{hHH}$和$κλ_{HHH}$。数值计算完成的预期在ILC与质心能量500，1000，1600 $GeV$和光度1000 $fb^{-1}$的能量。通道$e^{+}e^{-}\to b \bar b h_ih_i$和$e^{+}e^{-}\to t \bar t h_ih_i$也被讨论到质心能量为3 $TeV$和亮度为1000 $fb^{-1}$和5000 $fb^{-1}$。
We estimate the expected precision at a multi-TeV muon collider for measuring the Higgs boson couplings with electroweak gauge bosons, $HVV$ and $HHVV\ (V=W^\pm,Z)$, as well as the trilinear Higgs self-coupling $HHH$. At very high energies both single and double Higgs productions rely on the vector-boson fusion (VBF) topology. The outgoing remnant particles have a strong tendency to stay in the very forward region, leading to the configuration of the "inclusive process" and making it difficult to isolate $ZZ$ fusion events from the $WW$ fusion. In the single Higgs channel, we perform a maximum…
Top squark and neutralino decays in a R-parity violating model constrained by neutrino oscillation data
在具有三个双线性耦合$μ_i$和三个三线性耦合$λ'_{i33}$（其中$i$是轻子指数）的中微子质量的R宇称破坏（RPV）模型中，我们发现了六种一般的情形，每种情形都具有与振荡数据一致的三线性耦合的独特模式.这些模式可以反映在较轻的顶夸克的直接RPV衰变中，或者反映在最轻的超粒子（假设是最轻的中性伴子）的RPV衰变中。在Tevatron RUN II和LHC的典型信号大小进行了估计，结果是令人鼓舞的。
We explore the discovery potential of Higgs pair production at a 100 TeV collider via full leptonic mode. The same mode can be explored at the LHC when Higgs pair production is enhanced by new physics. We examine two types of fully leptonic final states and propose a partial reconstruction method. The reconstruction method can reconstruct some kinematic observables. It is found that the $m_{T2}$ variable determined by this reconstruction method and the reconstructed visible Higgs mass are important and crucial to discriminate the signal and background events. It is also noticed that a new vari…
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 a…
We discuss a scenario of the type-II 2HDM in which the $b\bar{b}γγ$ rate of the Higgs pair production is enhanced due to the two nearly degenerate 125 GeV Higgs bosons ($h$, $H$). Considering various theoretical and experimental constraints, we figure out the allowed ranges of the trilinear couplings of these two Higgs bosons and calculate the signal rate of $b\bar{b}γγ$ from the productions of Higgs pairs ($hh$, $hH$, $HH$) at the LHC. We find that in the allowed parameter space some trilinear Higgs couplings can be larger than the SM value by an order and the production rate of $b\bar{b}γγ$ …
Di-Higgs Production and Trilinear Higgs Self-Coupling in the scNMSSM: Qualitative Implications for the Electroweak Phase Transition at large λ and Low tan\b{eta}
The Compact Linear Collider (CLIC) is a future electron-positron collider that will allow measurement of the trilinear Higgs self-coupling in double Higgs boson events produced at its high-energy stages with collision energies of $\sqrt{s}$ = 1.5 and 3 TeV. The sensitivity to the Higgs self-coupling is driven by the measurements of the cross section and the invariant mass distribution of the Higgs-boson pair in the W-boson fusion process, e$^+$e$^-\to$HH$ν_e \barν_e$. It is enhanced by including the cross-section measurement of ZHH production at 1.5 TeV. The expected sensitivity of CLIC for Hi…
In an effective operator approach, the full set of leading contributions to anomalous top couplings comprises various new trilinear as well as higher interaction vertices, some of which are related to one another by gauge symmetry or equations of motion. In order to study trilinear top couplings to SM gauge bosons such as ttA, ttZ, tbW and ttg, the operator set can be restricted accordingly. However, the complete basis cannot be mapped onto an on-shell parametrisation of the trilinear vertices alone. Four-fermion contact terms qqtt and udtb must be included if the relation to the operator basi…
CP Violation in Top Quark Pair Production at Hadron Colliders
研究了在未来的2 TeV $p\bar p$ Tevatron和14 TeV $pp$ LHC对撞机上产生顶夸克对的CP破坏效应。我们研究了三种CP破坏源：终止三线性软破缺项$arg(A_t)$的超对称CP奇相位，标准模型双Higgs二重态扩展（2 HDM）中的CP奇参数，以及与模型无关的顶夸克色电偶极矩（CEDM）.最佳观测以及简单的观测。我们发现，在2 TeV的Tevatron上，当$m_{\tilde{g}}\sim 200$ GeV时，在$\sim 30fb^{-1}$积分光度下，可以观察到顶夸克对产生过程中$arg(A_t)$的CP破坏效应.在实验系统误差足够小的情况下，采用$\sim 150fb^{-1}$的大型强子对撞机可以利用最优观测量对2 HDM中的相位$arg(A_t)$和CP-奇参数进行$10^{-1}$阶数限制。在Tevatron上测量顶夸克的CEDM可以达到$10^{-18} cm g_s$的精度，而在LHC上可以达到$\times 10^{-20} cm g_s$的精度。
It is shown that MSSM with first two generations of squarks and sleptons much heavier than the third one naturally predicts the maximal stop mixing as a consequence of the RG evolution, with vanishing (or small) trilinear coupling at the high scale. The Higgs boson is generically heavy, in the vicinity of 125 GeV. In this inverted hierarchy scenario, motivated by the supersymmetric FCNC problem and models for fermion masses based on horizontal symmetries, the mass of the lightest stop is O(0.5) TeV and of gluino - O(2-3) TeV. The LSP can be either higgsino or bino or a mixture of both and it c…
Now that the Higgs boson has been observed by the ATLAS and CMS experiments at the LHC, the next important step would be to measure accurately its properties to establish the details of the electroweak symmetry breaking mechanism. Among the measurements which need to be performed, the determination of the Higgs self-coupling in processes where the Higgs boson is produced in pairs is of utmost importance. In this paper, we discuss the various processes which allow for the measurement of the trilinear Higgs coupling: double Higgs production in the gluon fusion, vector boson fusion, double Higgs-…
We have analysed the early LHC signatures of the minimal supergravity (mSUGRA) model. Our emphasis is on the 7 - $TeV$ run corresponding to an integrated luminosity of $\sim 1.0 ~fb^{-1}$ although we have also discussed briefly the prospects at LHC-10 $TeV$. We focus on the parameter space yielding relatively light squark and gluinos consistent with the darkmatter relic density data and the LEP bounds on the lightest Higgs scalar mass. This parameter space is only allowed for non-vanishing trilinear soft breaking term $A_0$. A significant region of the parameter space with large to moderate ne…
We analyze the Tevatron and Large Hadron Collider (LHC) reach for the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM) in the presence of explicit CP-violation. Using the most recent studies from the Tevatron and LHC collaborations, we examine the CPX benchmark scenario for a range of CP-violating phases in the soft trilinear and gluino mass terms and compute the exclusion/discovery potentials for each collider on the $(M_{H^+}, \tanβ)$ plane. Projected results from Standard Model (SM)-like, non-standard, and charged Higgs searches are combined to maximize the statistical signi…
We consider the ratio of cross sections of double-to-single Higgs boson production at the Large Hadron Collider at 14 TeV. Since both processes possess similar higher-order corrections, leading to a cancellation of uncertainties in the ratio, this observable is well-suited to constrain the trilinear Higgs boson self-coupling. We consider the scale variation, parton density function uncertainties and conservative estimates of experimental uncertainties, applied to the viable decay channels, to construct expected exclusion regions. We show that the trilinear self-coupling can be constrained to b…
We study dark matter (DM) production in the mono-Z channel at the 13 TeV LHC both in an effective field theory framework as well as in simplified models with vector mediators, using a multivariate analysis. For DM-quark effective operators with scalar, vector, and tensor couplings and DM mass of 100 GeV, the 5$σ$ reach in the DM interaction scale $Λ$ is around 2, 1, and 3 TeV, respectively, for 3 ab$^{-1}$ and assuming a 5\% systematic uncertainty on the total background normalization. For simplified models with leptophobic vector mediators, the 5$σ$ reach for the mass of the mediator is 1.7 T…
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 a…
We study the detectability of the stoponium in the di-Higgs decay mode at the photon-photon collider option of the International $e^+e^-$ Linear Collider (ILC), whose center-of-mass energy is planned to reach $\sim 1$ TeV. We find that $5σ$ detection of the di-Higgs decay mode is possible with the integrated electron-beam luminosity of $1 {\rm ab}^{-1}$ if the signal cross section, $σ(γγ\rightarrow σ_{\tilde{t}_1} \rightarrow hh)$, of ${\cal O}(0.1)$ fb is realized for the stoponium mass smaller than $\sim$ 800 GeV at 1 TeV ILC. Such a value of the cross section can be realized in the minimal …
We investigate the effect of top trilinear operators in t tbar production at the ILC. We find that the sensitivity to these operators largely surpasses the one achievable by the LHC either in neutral or charged current processes, allowing to probe new physics scales up to 4.5 TeV for a centre of mass energy of 500 GeV. We show how the use of beam polarisation and an eventual energy upgrade to 1 TeV allow to disentangle all effective operator contributions to the Ztt and gamma tt vertices.
The measurement of Higgs pair production will be a cornerstone of the LHC program in the coming years. Double Higgs production provides a crucial window upon the mechanism of electroweak symmetry breaking and has a unique sensitivity to the Higgs trilinear coupling. We study the feasibility of a measurement of Higgs pair production in the $b\bar{b}b\bar{b}$ final state at the LHC. Our analysis is based on a combination of traditional cut-based methods with state-of-the-art multivariate techniques. We account for all relevant backgrounds, including the contributions from light and charm jet mis…
In recent years it has been learned that scalar superpartner masses and trilinear couplings should both generically be larger than about 20 TeV at the short distance string scale if our world is described by a compactified string or M-theory with supersymmetry breaking and stabilized moduli. Here we study implications of this, somewhat generally and also in detail for a particular realization (compactification of M-theory on a G_2 manifold) where there is significant knowledge of the superpotential and gauge kinetic function, and a light gluino. In a certain sense this yields an ultraviolet co…
The quartic self-coupling of the Standard Model Higgs boson can only be measured by observing the triple-Higgs production process, but it is challenging for the Large Hadron Collider (LHC) Run 2 or International Linear Collider (ILC) at a few TeV because of its extremely small production rate. In this paper, we present a detailed Monte Carlo simulation study of the triple-Higgs production through gluon fusion at a 100 TeV hadron collider and explore the feasibility of observing this production mode. We focus on the decay channel $HHH\rightarrow b\bar{b}b\bar{b}γγ$, investigating detector effec…
Measuring the shape of the Higgs boson potential is of paramount importance and will be a challenging task at current as well as future colliders. While the expectations for the measurement of the trilinear Higgs self-coupling are rather promising, an accurate measurement of the quartic self-coupling interaction is presently considered extremely challenging even at a future 100 TeV proton-proton collider. In this work we explore the sensitivity that a muon collider with a center of mass energy in the multi-TeV range, and luminosities of the order of 10^35cm^-2s^-1, as presently under discussio…
