Models predicting the production and decay of supersymmetric (SUSY) particles often have promising search channels involving decays through heavy intermediate states such as top quarks and heavy bosons. However, unlike in most exotics scenarios these heavy states are only moderately boosted which can make traditional substructure techniques less useful and motivates the development of...
Beyond the standard model theories like Extra-Dimensions and Composite Higgs scenarios predict the existence of very heavy resonances compatible with a spin 0 (Radion),spin 1 (W’, Z’) and spin 2 (Graviton) particle with large branching fractions in pairs of standard model bosons and negligible branching fractions to light fermions. We present an overview of searches for new physics containing...
Several theories beyond the standard model predict new particles decaying resonantly into dibosons or coupling to dark matter particles. Jet substructure and boson tagging techniques play a crucial role in searches for dark matter and diboson resonances in boosted topologies. In this talk, the application of these techniques at ATLAS will be discussed in the context of recent searches for dark...
We present a search for new massive particles (such as Z prime and W prime resonances) decaying to heavy-flavour quarks with the CMS detector at the LHC, and dark matter signatures involving boosted jets. Resonant ttbar, tb, and heavy quark plus vector-like quark production, along with missing pt plus boosted objects, are investigated. We use proton-proton collision data recorded at a...
Several models of physics beyond the Standard Model contain preferential couplings to top quarks. We present an overview of searches for new physics containing boosted top quarks in the final state, using proton-proton collision data collected with the ATLAS detector at the LHC at a centre-of-mass energy of 13 TeV. These results cover heavy gauge bosons, excited third generation quarks, or...
We present results of searches for massive top and bottom quark partners using proton-proton collision data collected with the CMS detector at the CERN LHC at a center-of-mass energy of 8 and 13 TeV. These considered models include vector-like quarks, excited quarks and supersymmetric quark partners. These particles can be produced singly or in pair and their decays result in a variety of...
I will discuss fractal jet observables, which are collinear-unsafe but can be described by generalizing the formalism of fragmentation functions. Generalized fragmentation functions (GFFs) are nonperturbative objects with a calculable RG running. In contrast to the linear DGLAP equations for ordinary fragmentation functions, GFFs evolve nonlinearly, since they encode correlations among subsets...
In this talk, we introduce a new jet substructure method based on a
recursive iteration of the Soft Drop algorithm through both branches
of the clustering tree.
Recursive soft drop uses an additional parameter N to define the
number of layers of soft drop declustering, providing an optimized
grooming strategy for boosted objects with (N+1)-prong decays, as well
as improved stability in high...
In this talk, I present the first analysis of the substructure of jets using the 2010 CMS Open Data. Our analysis is based on 36/pb of 7 TeV proton-proton collisions, where in each event the leading jet has a transverse momentum larger than 150 GeV. We measure classic jet substructure observables like jet mass and multiplicity and compare the results to parton shower generators. We find...
We present the first calculations of the momentum sharing and angular separation distributions between the leading subjets inside a reconstructed jet, as well as the jet mass distribution modification in heavy ion collisions. These observables are sensitive to the early and late stages of the in-medium parton shower evolution and allow us to probe the quark-gluon plasma across a wide range of...
We derive the electroweak (EW) collinear splitting functions up to single logs. Especially we systematically incorporate EW symmetry breaking (EWSB), by imposing a particularly convenient gauge choice (dubbed “Goldstone Equivalence Gauge”) that disentangles the effects of Goldstone bosons and gauge fields in the presence of EWSB. As a result, we are able to derive splitting functions up to...
We show how the top mass can be extracted kinematically using cross sections for event shapes observables calculated using effective field theory methods. With the help of Soft Drop grooming done at a level that does not disturb the radiation that can modify the top mass definition, while still isolating the top jet, we obtain a distribution that is only mildly sensitive to the underlying...
We introduce the first use of deep neural network-based generative modeling for high energy physics (HEP). Our novel Generative Adversarial Network (GAN) architecture is able cope with the key challenges in HEP images, including sparsity and a large dynamic range. For example, our Location-Aware Generative Adversarial Network learns to produce realistic radiation patterns inside high energy...
We perform a phenomenological study of the invariant mass distribution of hadronic jets produced in pp collisions, in conjunction with a groomer, in particular the modified MassDrop Tagger (equivalent to Soft Drop with angular exponent $\beta = 0$). Our calculation resums large logarithms of the jet mass and includes the full dependence on the groomer’s energy threshold $z_\text{cut}$ , and it...
Boosted topologies allow to explore Standard Model processes in kinematical regimes never tested before. In such LHC challenging environments, standard reconstruction techniques quickly hit the wall. Targeting hadronic final states means to properly reconstruct energy and multiplicity of the jets in the event. In order to be able to identify the decay product of boosted objects, i.e. W bosons,...
A number of measurements are presented that utilize and/or investigate jet substructure.
The measurement of top production and the investigation of its properties in the boosted regime is gaining increasing attention with the rapid increase of the production cross sections at 13 TeV. The CMS experiment has measured the production cross section as function of the transverse momentum and...
Charged track multiplicity is among the most powerful observables for discriminating quark- from gluon-initiated jets. Despite its utility, it is not infrared and collinear (IRC) safe, so perturbative calculations are limited to studying the energy evolution of multiplicity moments. While IRC-safe observables, like jet mass, are perturbatively calculable, their distributions often exhibit...
Distinguishing quark-initiated from gluon-initiated jets is useful for many measurements and searches at the LHC. We present a quark-initiated versus gluon-initiated jet tagger from the ATLAS experiment using the number of reconstructed charged particles inside the jet. The measurement of the charged-particle multiplicity inside jets from Run 1 is used to derive uncertainties on the tagger...
Distinguishing between quark and gluon initiated jets relies on differences in the QCD shower patterns and is an important ingredient for a number of physics analyses. We present the current status of quark gluon tagging in CMS including comparisons using 13 TeV collision data.
We present a phenomenological study of the Higgs radiative decay to a fermion pair. We include the chirality-flipping diagrams via the Yukawa couplings at the order $\mathcal{O}(y_f^2 \alpha)$, the chirality-conserving contributions via the top-quark loops of the order $\mathcal{O}(y_t^2 \alpha^3)$, and the electroweak loops at the order $\mathcal{O}(\alpha^4)$. All the leptonic radiative...
We study the Higgs boson (h) decay to two light jets at the 14 TeV High-Luminosity-LHC (HL-LHC), where a light jet (j) represents any non-flavor tagged jet from the observational point of view. The decay mode h→gg is chosen as the benchmark since it is the dominant channel in the Standard Model (SM), but the bound obtained is also applicable to the light quarks (j=u,d,s). We estimate the...
Small radius jets with R = 0.4 are standard tools in ATLAS for physics analysis. They are calibrated using a sequence of Monte Carlo simulation-derived calibrations and corrections followed by in-situ calibrations based on the transverse momentum balance between the probed jets and well-measured reference signals. In this talk the inputs to jet reconstruction in LHC Run 2 comprising...
Measurement of jet energy scale corrections and resolution, and performance of jet mass scale and resolution based on data collected at a center-of-mass energy of 13 TeV are presented in this report. Jet energy scale corrections at CMS accounts for the effects of pileup, and dependencies of response of jets on transverse momenta and detector non-uniformity. The differences in response measured...
Large-R jets are used by many ATLAS analyses working in boosted regimes. ATLAS Large-R jets are reconstructed from locally calibrated calorimeter topoclusters with the Anti-k_{t} algorithm with radius parameter R=1.0, and then groomed to remove pile-up with the trimming algorithm with f_{cut} 0.05 and subjet radius R=0.2. Monte Carlo based energy and mass calibrations correct the...
The case of CMS "two prong" tagging algorithms are presented, specifically detailing the cases of W and H boson tagging. This talk will focus on the most recent algorithms used in LHC Run II analyses and their validation in data.
We present updates of W, Top and Higgs tagging studies with the ATLAS detector. The performance of 2 variable taggers, HEPTopTagger and shower deconstruction are compared in Monte Carlo simulations. To asses the modelling of the taggers’ performance, the tagging efficiencies are measured, with the full 2015+2016 dataset, in semi-leptonic top quark pair events and the background rejections are...
An overview of methods for identifying decays of boosted top quarks with the CMS detector in Run II is presented.
The performance of standard tagging algorithms begins to fall in the case of highly boosted B hadrons (γβ=p/m>200). This work builds on our previous study that uses the jump in hit multiplicity among the pixel layers of an ATLAS or CMS-like detector when a B hadron decays within the detector volume. Consequently, tracking is not required.
First, multiple pp interactions within a finite...
Machine learning based on convolutional neural networks can be used to study jet images from the LHC. Top tagging in fat jets offers a well-defined framework to establish our DeepTop approach and compare its performance to QCD-based top taggers. We optimize a network architecture to identify top quarks in Monte Carlo simulations of the Standard Model production channel. Using standard fat...
We present techniques for the identification of hadronically-decaying W bosons and top quarks using high-level features as inputs to boosted decision trees and deep neural networks in the ATLAS experiment at sqrt(s)=13 TeV. The performance of these machine learning based taggers is compared in Monte Carlo simulation with various different tagging algorithms. An improvement in background...
Machine learning has become an important tool in particle physics, and in jet substructure and boosted objects in particular. This presentation shows the breadth of applications from CMS, from "DeepFlavor" b-tagging to new techniques of substructure applications.
We develop a new pileup mitigation technique based on multi-channel jet images using convolutional neural nets. The input to the network is a three-channel jet image: the calorimeter "pixel" information of charged leading vertex particles, charged pileup particles, and neutral particles . We compare our algorithm to existing methods on a wide range of simple and complex jet observables up to...
Pileup is one of the biggest challenges facing the LHC and HL-LHC physics programs. Many reconstruction methods have been proposed for mitigating its effects across a broad range of physics metrics such as jet and jet substructure response and resolution, missing transverse energy performance, and lepton identification. Among the most successful are the SoftKiller and Pileup Per Particle...
Simultaneous proton-proton collisions, or pileup, at the LHC has a significant impact on jet reconstruction, requiring the use of advanced pileup mitigation techniques. Pileup mitigation may occur at several stages of the reconstruction process, and ATLAS uses a combination of schemes, including constituent reconstruction methods, constituent-level pileup-mitigation techniques, and jet-level...
We present tools developed by CMS for LHC Run II designed for pileup mitigation in the context of jets, MET, lepton isolation, and substructure tagging variables. Pileup mitigation techniques of "Pileup per particle ID" (PUPPI), and pileup jet identification are presented in detail along with the validation in data.
The High-Luminosity LHC aims to provide a total integrated luminosity of 3000/fb from proton-proton collisions at sqrt(s) = 14 TeV over the course of ~10 years, reaching instantaneous luminosities of up to L = 7.5 x 10^34/cm^2/s, corresponding to an average of 200 inelastic p-p collisions per bunch crossing (mu = 200). Fast simulation studies have been carried out to evaluate the prospects of...
The prospects for boosted physics and jet substructure at the HL-LHC are presented, along with technical capabilities and updates to the detector that will assist in these measurements and searches.
The Compact Linear Collider project envisages an electron-positron collider
with a low-energy stage at sqrt(s) = 380 GeV and an ultimate center-of-mass
reach up to 3 TeV. Detailed Monte Carlo simulation studies of the detector
are performed to optimize the design of the experiment and to understand
the physics potential. CLIC aims to meet the challenging requirements on
jet reconstruction...
We discuss performance requirements for future detectors in the context of reconstruction of multi-TeV objects (single particles and jets) at a 100 TeV collider. A software framework based on a Geant4 simulation together with a realistic reconstruction of tracks and calorimeter clusters is presented. Using this framework, we discuss response and momentum resolution of the tracker and the...
We introduce a new scale-invariant jet clustering algorithm which does not impose a fixed cone size on the event. The proposed construction maintains excellent object discrimination for very collimated partonic systems. Nevertheless, it is able to asymptotically recover favorable behaviors of the standard anti-KT algorithm. Additionally, it is intrinsically suitable for the tagging of highly...
Since the machine learning techniques are improving rapidly, it has been shown that the image recognition technique can be used to detect jet substructure. And it turns out that deep neural networks can match or outperform traditional approach. To push it further, we investigate the Recursive Neural Networks (RecNN), which embeds jet clustering history recursively as in natural language...
We present a novel approach to the problem of discriminating jets produced from the hadronic decays of highly-boosted heavy particles (top, W, Z, H) from light jets. By hypothesizing different particle origins for the jets and boosting all jet constituents into the corresponding rest frames, angular and kinematic distributions of reconstructed particles can be used to discriminate 2- or...
