Daniel Wicke
The D0 experiment has searched for phenomena beyond the standard model in top quark events. The methods and results of four analyses covering various possible deviations from the standard model behaviour are discussed. With data sets covering up to 2.1fb^-1 no deviation from the standard model expectations could be found.
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The LHC experiments have searched for and excluded many proposed Beyond the Standard Model (BSM) theories. However, there are many scenarios where LHC has little or no sensitivity. Electron-positron colliders offers a different avenue for searches for such phenomena.In this talk, we will review the expectations for searches for number of BSM models at the International Linear Collider (ILC). We will discuss new Higgs-like scalars, indirect BSM via Standard Model Effective Field Theory (SMEFT) fits, mono-photons, and SUSY in strongly or moderately compressed models.
A comprehensive review of the recent results on measurements of single top-quark production cross-sections at $\sqrt{s} =$ 7, 8 and 13 TeV performed by the ATLAS and CMS Collaborations is presented. The cross-section measurements include inclusive, fiducial and differential results. In addition, the latest measurements, based on angular distributions in $t$-channel single-top-quark processes, of the top-quark polarisation and $W$ boson spin observables at $\sqrt{s} =$ 8 TeV, and the analyses of the $Wtb$ vertex at $\sqrt{s} =$ 7 and 8 TeV are also discussed. All measurements are in good agreem…
Application of Machine Learning Based Top Quark and W Jet Tagging to Hadronic Four-Top Final States Induced by SM as well as BSM Processes
本文在 DELPHES 模拟的四顶夸克强子末态中，利用梯度提升和子喷流度变量实现顶夸克与 W 喷流标记，并相较切割方法改进标量共振重建。
This topical group focuses on searches for signals from physics Beyond the Standard Model (BSM), both from a theoretical and experimental perspective, including neutrino-related BSM and searches for BSM in other sectors using neutrino facilities.
Machine Learning Based Top Quark and W Jet Tagging to Hadronic Four-Top Final States Induced by SM as well as BSM Processes
本研究将选定的机器学习技术应用于强子型四顶夸克末态的顶夸克与W喷注标记，结合模拟事件和参数化探测器模拟开展实验，并与基于切割的方法进行对比。
On the BSM reach of four top production at the LHC
本文研究 LHC 四顶夸克末态探测 BSM 的能力，利用图神经网络提升 SM 分析性能，并借助四顶末态规避胶子融合中的相消干涉，增强双 Higgs 二重态模型等排除能力。
A review of the discovery potential of LHC for new phenomena beyond the Standard Model (BSM) other than Supersymmetry in the early phase of running is presented. Topics covered include searches for extra dimensions in different scenarios (ADD, Randall-Sundrum, black holes ...), resonance hunting in di-lepton, di-photon and di-jet final states, searches for contact interactions, heavy stable charged particles, technicolor, etc. The strategies of the ATLAS and CMS experiments to understand the detectors and prepare them for "search" mode and the prospects for discoveries using early data are des…
In this article we study a Standard Model extension modifying the top-quark Yukawa coupling to the Higgs boson by allowing a mixture of CP-odd and -even couplings. Single top-quark production in association with an additional Higgs boson provides a natural laboratory to search for such extensions. However, because of the small cross section the experimental analysis is challenging. Already the measurement of the cross section for this process is highly non-trivial. Furthermore, using only cross section measurements, a certain parameter region would escape detection. Using an explicit BSM scena…
Application of Machine Learning Based Top Quark and W Jet Tagging to Hadronic Four-Top Final States Induced by SM and BSM Processes
本文在Delphes模拟框架下对比截断与机器学习喷注标记方法，识别顶夸克和W喷注，用于标准模型及新物理标量共振y0的全强子四顶夸克末态，重建不变质量并比较背景抑制性能，为LHC搜索提供参考。
Many models of physics beyond the Standard Model (SM) contain enhanced couplings to third generation particles. The predicted signatures include vector-like quarks and $t\bar{t}$ resonances. We present a review of non-SUSY based searches for new physics beyond the SM in final states with third-generation quarks using proton-proton collision data collected with the CMS detector at the CERN LHC. We analyze a wide range of final states, from multi-leptonic to entirely hadronic, and many results use novel analysis techniques to identify and reconstruct highly boosted final states that are created …
Many theories, from Supersymmetry to models of Strong Electroweak Symmetry Breaking, look at the production of four top quarks as an interesting channel to evidentiate signals of new physics beyond the Standard Model. The production of four-top final states requires large partonic energies, above the 4mt threshold, that are available at the CERN Large Hadron Collider and will become more and more accessible with increasing energy and luminosity of the proton beams. A good theoretical control on the Standard Model background is a fundamental prerequisite for a correct interpretation of the poss…
Top quark properties measurements and searches at ATLAS and CMS
本文报告了ATLAS和CMS实验中顶夸克性质的最新测量结果以及对超出标准模型物理的新搜索结果。
Search for Physics beyond the Standard Model in four- and three-top quark production
该研究利用CMS实验数据重新分析四顶夸克产生，以探索超出标准模型的物理现象，包括对有效场论算符、重共振和顶-Yukawa耦合的约束，并展示了多顶夸克最终态对新物理的灵敏度。
The study of Higgs boson production at large transverse momentum is one of the new frontiers for the LHC Higgs physics programme. This paper considers boosted Higgs production in the Standard Model Effective Field Theory (SMEFT). We focus on the gluon fusion and $t{\bar t}H$ production processes and study the effects of three dimension-6 operators: the top Yukawa operator, the gluon-Higgs effective coupling and the chromomagnetic dipole operator of the top quark. We perform a detailed study of the sensitivity of current and future LHC data to the corresponding Wilson coefficients, consistently…
In this talk I discuss the widespread impact of the top quark on phenomena in elementary particle physics as codified through the Standard Model (SM), its important role in motivating the possiblity of physics beyond the Standard Model (BSM), and its use as a signal for detailed studies of the SM and searches for BSM physics.
BSM patterns in scalar-sector coupling modifiers
本研究针对标量区希格斯耦合修正因子展开，评估了当前及未来对撞机上弱玻色子希格斯对产生过程的费曼拓扑分析灵敏度，探索BSM模型在耦合偏离空间的特征，为未来BSM物理鉴别提供了方向。
In models with extended scalars and CP violation, resonance searches in double Higgs final states stand in competition with related searches in top quark final states as optimal channels for the discovery of beyond the Standard Model (BSM) physics. This complementarity is particularly relevant for benchmark scenarios that aim to highlight multi-Higgs production as a standard candle for the study of BSM phenomena. In this note, we compare interference effects in $t\bar t$ final states with correlated phenomena in double Higgs production in the complex singlet and the complex 2-Higgs-Doublet Mod…
New developments in both the theories and experiments related to the extraction of the top-row Cabibbo-Kobayashi-Maskawa matrix elements $V_{ud}$ and $V_{us}$ led to a series of new anomalies, for instance the apparent violation of the top-row unitarity relation. It is important to further reduce all the associated Standard Model theory uncertainties in order to better understand whether such observations point towards the possibility of physics beyond the Standard Model, or rather some unexpectedly large Standard Model effects. This requires improved studies of tree-level and higher-order Sta…
FCC-hh is a proposed future energy-frontier hadron collider, which goal is to provide high luminosity proton collisions at a centre-of-mass energy of 100 TeV. The FCC-hh has an extremely rich physics program ranging from standard model (SM) measurements to direct searches for physics beyond the standard model (BSM). One of the processes sensitive to new physics is flavour-changing neutral currents (FCNC) that extremely rare in the SM but have enhanced behavior in several BSM scenarios. In this report we present results of projections of FCNC searches in top quark interactions to the FCC-hh con…
Boosted and semi-boosted all-hadronic $t\bar{t}$ reconstruction performance on kinematic variables for selected BSM models using a 2D extesion of the BumpHunter algorithm
本研究提出BumpHunter算法的二维扩展，用于增强型和半增强型全强子$t\bar{t}$末态重建，在BSM模型下提高信号灵敏度并识别对喷注能量校准不敏感的关键变量。
Charged Higgs boson can exist in many physics beyond the standard models (BSM) and it is the obvious BSM signal. We briefly describe why the 125GeV scalar discovered at the LHC must have (heavy) companion: the charged Higgs boson, in a new paradigm. We then focus on the charged Higgs phenomenology, especially on how to measure $\tanβ$ precisely utilizing the top quark polarization information.
Despite strong experimental evidences for their conservation at low energies, the baryon $B$ and lepton $L$ numbers are not expected to be absolute symmetries. Already violated in the Standard Model (SM) by non-perturbative effects (tiny at low temperatures and energies) and not justified by any fundamental principle, $B$ and $L$ appear naturally violated in beyond the Standard Model (BSM) scenarios, e.g. in supersymmetry (SUSY). The fact that any violation remained unobserved at low energies can nonetheless be explained, without pushing the associated characteristic sale beyond the TeV, by us…
Probing EFT models using top quark production in multilepton final states
本研究利用CMS探测器多轻子末态顶夸克产生数据，在EFT框架下通过26个维度六算子搜寻BSM物理，结果与标准模型预言一致。
The top quark is the heaviest known elementary particle of the Standard Model (SM) of particle physics and, therefore, it is expected to have large couplings to hypothetical new physics in many models beyond the SM (BSM). Various studies have predicted the presence of multi-lepton anomalies at the LHC. One of those anomalies is the excess production of two same-sign leptons and three isolated leptons in association with $b$-jets. These are reasonably well described by a 2HDM+$S$ model, where $S$ is a singlet scalar. Both the ATLAS and CMS experiments have reported sustained excesses in these f…
We have searched for production of t-tbar pairs in p-pbar interactions at 1.8 TeV center-of-mass energy at the FNAL Tevatron collider. The search assumes standard model decay for top quark into W + b quark. We observe in e+jet and mu+jet final states a small, not statistically significant, excess above the background estimated by two different methods. The results presented are preliminary.
Various BSM models predict large deviations of the top electroweak couplings. Many examples will be given emphasizing the need for precise and model independent measurements of these couplings. Here I address the question of compatibility between theoretical predictions and the LEP/SLC/Tevatron constraints which, through loop effects, allow setting very significant constraints on these predictions. A Randall Sundrum inspired prediction will be discussed in more details. Finally the prospects offered by LHC and ILC measurements for top EW couplings are briefly reviewed.
Single top production in e+e- annihilations is searched for in data collected by the L3 detector at centre-of-mass energies from 189 to 209 GeV, corresponding to a total integrated luminosity of 634 pb-1. Investigating hadronic and semileptonic top decays, no evidence of single top production at LEP is obtained and upper limits on the single top cross section as a function of the centre-of-mass energy are derived. Limits on possible anomalous couplings, as well as on the scale of contact interactions responsible for single top production are determined.
Effective field theories provide a model independent parametrization of the physics beyond the SM if the new degrees of freedom are heavy and complement thus the searches for resonances. In this talk, I will apply this method to the top sector which is expected to play a special role in many BSM scenarios. I will then show the effects of those dimension-six operators on cross-sections and distributions at hadron colliders. Those results together with the present data from the LHC and the Tevatron already constrain the parameter space
Vector-like quarks (VLQ) that couple preferentially to third-generation Standard Model (SM) quarks are a well-motivated extension of the SM, which could solve in particular the hierarchy problem. While VLQs can be produced in pairs via the strong interaction at the LHC, the cross section for single production may be larger than the pair production cross section for VLQ masses above the current exclusion limits. An overview of the searches for the single production of VLQs at the ATLAS experiment that use data taken at a centre-of-mass energy of 13 TeV, corresponding to up to 79.8 fb$^{-1}$, is…
The precise measurement of top quark production and properties is one of the primary goals of the Tevatron during Run II. The total top-antitop production cross-section has been measured in a large variety of decay channels and using different selection criteria. Results from differential cross-section measurements and searches for new physics in top-antitop production and top quark decays are available. Electroweak production of single top quarks has been searched for. The results from all these analyses, using typically 200/pb of data, are presented.
Two related searches for phenomena beyond the standard model (BSM) are performed using events with hadronic jets and significant transverse momentum imbalance. The results are based on a sample of proton-proton collisions at a center-of-mass energy of 13 TeV, collected by the CMS experiment at the LHC in 2016-2018 and corresponding to an integrated luminosity of 137 fb$^{-1}$. The first search is inclusive, based on signal regions defined by the hadronic energy in the event, the jet multiplicity, the number of jets identified as originating from bottom quarks, and the value of the kinematic va…
We present a general procedure to decompose Beyond the Standard Model (BSM) collider signatures presenting a Z2 symmetry into Simplified Model Spectrum (SMS) topologies. Our method provides a way to cast BSM predictions for the LHC in a model independent framework, which can be directly confronted with the relevant experimental constraints. Our concrete implementation currently focusses on supersymmetry searches with missing energy, for which a large variety of SMS results from ATLAS and CMS are available. As show-case examples we apply our procedure to two scans of the minimal supersymmetric …
We describe the results of four new searches based on data samples from the 1992 - 1996 proton-antiproton 1.8 TeV Collider run at Fermilab. DZERO has searched for resonant slepton production in the two muon plus two jet channel. Using the R-parity violating mSUGRA model, smuon and smuon neutrino masses up to 280 GeV/c2 are excluded. CDF has searched for R-parity violating scalar top quark decays in two tau plus two jet events and set a mass limit of 119 GeV/c2. DZERO has searched for evidence of large extra dimensions in monojet production. Limits are set on M_D the fundamental mass scale, of …
We first review the decade-old, broad collider physics research program dubbed energy-peaks. We consider the energy distribution of a massless particle in the lab frame arising from the two-body decay of a heavy particle produced unpolarized, whose boost distribution is arbitrary. Remarkably, the location of the peak of this child particle's energy distribution is identical to its single-valued energy in the rest frame of the parent, which is a function of the parent's mass and that of the other decay product. We summarize generalizations to other types of decay and a variety of applications t…
We review the search for the top quark conducted by the D-Zero collaboration using data from the Fermilab pbar-p collider. Based upon a preliminary analysis of an integrated luminosity of about 13.5 pb-1, we have searched for t-tbar production and decay in the experimental channels involving a pair of dileptons (electron or muon) plus jets, or single leptons plus jets. Summed over all channels, we observe 7 events in our data, to be compared with an expectation from background processes of 3.2 +/- 1.1 events. The t-tbar ~cross-section deduced from the small excess of events is presented as a f…
Experimental tests of the Standard Model of particle physics (SM) find excellent agreement with its predictions. Since the original formation of the SM, experiments have provided little guidance regarding the explanations of phenomena outside the SM, such as the baryon asymmetry and dark matter. Nor have we understood the aesthetic and theoretical problems of the SM, despite years of searching for physics beyond the Standard Model (BSM) at particle colliders. Some BSM particles can be produced at colliders yet evade being discovered, if the reconstruction and analysis procedures not matched to…
We have searched for the supersymmetric partner of the top quark (stop) in 107 pb^{-1} of p-pbar collisions at \sqrt{s}= 1.8 TeV collected by the Collider Detector at Fermilab (CDF). Within the framework of the Minimal Supersymmetric extension of the Standard Model (MSSM) each of the pair-produced stops is assumed to decay into a lepton, bottom quark and supersymmetric neutrino. Such a scenario would give rise to events with two leptons, two hadronic jets, and a substantial imbalance of transverse energy. No evidence of such a stop signal has been found. We calculate a 95% confidence level (C.…
The top quark, being the heaviest particle of the Standard Model, is a prime candidate of where physics beyond the SM might currently hide before our eyes. There are many natural extensions of the SM that rely on top compositeness, and the top quark could follow the paradigm of revealing a substructure when it is probed at high enough momentum transfers. Observing high $p_T$ top final states naturally drives us towards boosted hadronic analyses that can be tackled efficiently with jet substructure techniques. In this paper we analyse the prospects of constraining exemplary non-standard QCD top…
ATLAS EFT Results in the Top Quark Sector
ATLAS利用Run-2数据集在13 TeV能量下，通过SMEFT分析顶夸克领域，提高Wilson系数的灵敏度并探索超出标准模型的效应。
The top partner as a hallmark of the Littlest Higgs model with $T$-parity (LHT model) has been extensively searched for during the Large Hadron Collider (LHC) Run-1. With the increasing mass limits on the top partner, the single production of the top partner will be dominant over the pair production. Under the constraints from the Higgs data, the electroweak precision observables and $R_b$, we find that the mass of $T$-even top partner ($T_+$) has to be heavier than 730 GeV. Then, we investigate the observability of the single $T$-even top partner production through the process $pp \to T_+ j$ …
The DO collaboration reports on a search for the Standard Model top quark in pbar-p collisions at Sqrt(s)=1.8TeV at the Fermilab Tevatron, with an integrated luminosity of approximately 50pb-1. We have searched for t-tbar production in the dilepton and single-lepton decay channels, with and without tagging of b-quark jets. We observed 17 events with an expected background of 3.8+/-0.6 events. The probability for an upward fluctuation of the background to produce the observed signal is 2.0E-6 (equivalent to 4.6 standard deviations). The kinematic properties of the excess events are consistent w…
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