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 interactions in this kinematical regime. We correctly include QCD modifications to additional gluon emission off the boosted top quark and keep track of the modified top tagging efficiencies. We conclude that non-standard top QCD interactions can be formidably constrained at the LHC 14 TeV. Experimental systematic uncertainties are a major obstacle of the described measurement. Unless significantly improved for the 14 TeV run, they will saturate the direct sensitivity to non-resonant BSM top physics at luminosities of around 100/fb.
Improving sensitivity of vectorlike top partner searches with jet substructure
Indian Institute of Technology Guwahati（印度理工学院古瓦哈提分校）；Indian Institute of Science Education and Research Kolkata（印度科学教育研究所加尔各答分校）；Indian Institute of Science Education and Research, Knowledge City, Sector 81, S. A. S. Nagar, Manauli PO 140306, Punjab, India（印度科学教育研究所旁遮普邦分校）；The Institute of Mathematical Sciences（数学科学研究所）
We apply techniques from Bayesian generative statistical modeling to uncover hidden features in jet substructure observables that discriminate between different a priori unknown underlying short distance physical processes in multi-jet events. In particular, we use a mixed membership model known as Latent Dirichlet Allocation to build a data-driven unsupervised top-quark tagger and $t\bar t$ event classifier. We compare our proposal to existing traditional and machine learning approaches to top jet tagging. Finally, employing a toy vector-scalar boson model as a benchmark, we demonstrate the p…
Manifest gauge-invariance requires that observable states in the standard-model are described by composite operators, which involve additional Higgs contributions beyond perturbation theory. This field-theoretical effect has been confirmed in lattice simulations. It should also be experimentally accessible at high enough precision. Here a few estimates for such signatures at current and future collider experiments will be discussed.
We propose a novel jet substructure observable of boosted tops that is related to the linear polarization of the $W$ boson in boosted top quark decay, which results in a $\cos2ϕ$ angular correlation between the $t\to bW$ and $W\to f\bar{f'}$ decay planes. We discuss in detail the origin of such linear polarization by applying Wigner's little group transformation. We show that the unique $\cos2ϕ$ angular correlation only exists in the boosted regime but not in the top quark rest frame. We construct an experimental observable for such correlation based on the transverse energy deposition asymmet…
Vectorlike quarks have been shown to resolve certain long-standing discrepancies pertaining to the bottom sector. We investigate, here, the prospects of identifying the existence of a topless vectorlike doublet $(B,~Y)$, as is preferred by the electroweak precision measurements. Concentrating on single production, $viz.$ $B \bar b$ with $B \to b + Z/H$ subsequently, we find that the fully hadronic decay-channel is susceptible to discovery provided jet substructure observables are used. At the 13 TeV LHC with an integrated luminosity of 300 fb$^{-1}$, a modest value of the chromomagnetic transi…
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…
Future experiments beyond the LHC era will measure high-momentum bosons ($W$, $Z$, $H$) and top quarks with strongly collimated decay products that form hadronic jets. This paper describes the studies of the performance of jet substructure variables using the Geant4 simulation of a detector designed for high energy $pp$ collisions at a 100 TeV collider. The two-prong jets from $Z' \rightarrow WW$ and three-prong jets from $Z' \rightarrow t\bar{t}$ are compared with the background from light quark jets, assuming $Z'$ masses in the range 5 -- 40 TeV. Our results indicate that the performance of …
The physics beyond the Standard Model with parameters of the compressed spectrum is well motivated both in a theory side and with phenomenological reasons, especially related to dark matter phenomenology. In this letter, we propose a method to tag soft final state particles from a decaying process of a new particle in this parameter space. By taking a supersymmetric gluino search as an example, we demonstrate how the Large Hadron Collider experimental collaborations can improve a sensitivity in these non-trivial search regions.
Searching for Heavy Charged Higgs Boson with Jet Substructure at the LHC
我们研究了在大型强子对撞机上产生的重荷希格斯玻色子（在这项研究中从800 GeV到1500 GeV）与顶夸克的碰撞能量为$\sqrt{s}=14$ TeV。这样一个重电荷的希格斯玻色子玻色子由于其大的汤川耦合，可以像MSSM一样主要衰变为顶夸克和底夸克。为了抑制背景事件并确认信号，我们重建了重电荷希格斯玻色子和相关顶夸克的质量隆起。为此，我们提出了一种混合R重建方法，它利用顶部标记技术，射流子结构技术开发的高度提升大质量粒子。以$p p \to H^{\pm} t \to t tb$的全强子模作为测试场，我们发现这种方法可以大大减少全重构中的组合运算，并成功地将背景事件降低到一个可控的水平。研究了LHC对重荷希格斯玻色子的灵敏度，发现当$b$时，能达到$9.5σ$意义.
The different modifications of quark- and gluon-initiated jets in the quark-gluon plasma (QGP) produced in heavy-ion collisions is a long-standing question that has not yet received a definitive answer from experiments. In particular, the relative sizes of the modification of quark and gluon jets differ between theoretical models. Therefore, a fully data-driven technique is crucial for an unbiased extraction of the quark and gluon jet spectra and substructure. We perform a proof-of-concept study based on proton-proton and heavy-ion collision events from the \textsc{Pyquen} generator with stati…
The modification of quark- and gluon-initiated jets in the quark-gluon plasma produced in heavy-ion collisions is a long-standing question that has not yet received a definitive answer from experiments. In particular, the size of the modifications in the quark-gluon plasma differs between theoretical models. Therefore a fully data-driven technique is crucial for an unbiased extraction of the quark and gluon jet spectra and substructure. Corroborating past results, I demonstrate the capability of a fully data-driven technique called topic modeling in separating quark and gluon contributions to …
Looking inside jets: an introduction to jet substructure and boosted-object phenomenology
Università di Genova（热那亚大学）；INFN, Sezione di Genova（意大利国家核物理研究所热那亚分部）；IPhT, CNRS, CEA Saclay, Université Paris-Saclay（巴黎萨克雷大学）；Institute of Particle Physics Phenomenology, Physics Department, Durham University（杜伦大学）
Recent measurements performed by the ATLAS and CMS collaborations on the Run 2 dataset are testing QCD with unprecedented precision. The wealth of data, an ever-improving experimental understanding of jets and photons, and novel measurements of jet substructure enable an improved understanding.
We examine the robustness of collider phenomenology predictions for a dark sector scenario with QCD-like properties. Pair production of dark quarks at the LHC can result in a wide variety of signatures, depending on the details of the new physics model. A particularly challenging signal results when prompt production induces a parton shower that yields a high multiplicity of collimated dark hadrons with subsequent decays to Standard Model hadrons. The final states contain jets whose substructure encodes their non-QCD origin. This is a relatively subtle signature of strongly coupled beyond the …
We study the effectiveness of theoretically-motivated high-level jet observables in the extreme context of jets with a large number of hard sub-jets (up to $N=8$). Previous studies indicate that high-level observables are powerful, interpretable tools to probe jet substructure for $N\le 3$ hard sub-jets, but that deep neural networks trained on low-level jet constituents match or slightly exceed their performance. We extend this work for up to $N=8$ hard sub-jets, using deep particle-flow networks (PFNs) and Transformer based networks to estimate a loose upper bound on the classification perfo…
In this paper we study aspects of top tagging from first principles of QCD. We find that the method known as the CMS top tagger becomes collinear unsafe at high $p_t$ and propose variants thereof which are IRC safe, and hence suitable for analytical studies, while giving a comparable performance to the CMS tagger. We also develop new techniques to identify three-pronged jet substructure, based on adaptations of the Y-splitter method and its combination with grooming. A novel feature of our studies, relative to previous calculations of two-pronged substructure, is our use of triple-collinear sp…
The tails of diboson production at the LHC are sensitive to the interference between Standard Model and higher dimension operators parameterizing the effects of heavy new physics. However, helicity selection rules for the diboson scattering amplitudes set an obstruction to the naïve interference contributions of dimension six operators, causing the total diboson rate correction's leading contribution to cancel. In this case, carefully measuring the azimuthal decay angles "resurrects" the interference, recouping sensitivity to the "non-interfering" operators. We explore these signatures in deta…
