scholarly journals Combining outlier analysis algorithms to identify new physics at the LHC

2021 ◽  
Vol 2021 (9) ◽  
Author(s):  
Melissa van Beekveld ◽  
Sascha Caron ◽  
Luc Hendriks ◽  
Paul Jackson ◽  
Adam Leinweber ◽  
...  
Keyword(s):  
Hadron Collider ◽  
Gaussian Mixture ◽  
New Physics ◽  
Outlier Analysis ◽  
Detection Techniques ◽  
Latent Space ◽  
Variational Autoencoder ◽  
Model Independent ◽  
Weighted Combination ◽  
Isolation Forest

Abstract The lack of evidence for new physics at the Large Hadron Collider so far has prompted the development of model-independent search techniques. In this study, we compare the anomaly scores of a variety of anomaly detection techniques: an isolation forest, a Gaussian mixture model, a static autoencoder, and a β-variational autoencoder (VAE), where we define the reconstruction loss of the latter as a weighted combination of regression and classification terms. We apply these algorithms to the 4-vectors of simulated LHC data, but also investigate the performance when the non-VAE algorithms are applied to the latent space variables created by the VAE. In addition, we assess the performance when the anomaly scores of these algorithms are combined in various ways. Using super- symmetric benchmark points, we find that the logical AND combination of the anomaly scores yielded from algorithms trained in the latent space of the VAE is the most effective discriminator of all methods tested.

Semi-supervised fabric defect detection based on image reconstruction and density estimation

2020 ◽  
pp. 004051752096673
Author(s):  
Qihong Zhou ◽  
Jun Mei ◽  
Qian Zhang ◽  
Shaozong Wang ◽  
Ge Chen
Keyword(s):  
Image Reconstruction ◽  
Density Estimation ◽  
Defect Detection ◽  
Gaussian Mixture ◽  
Inspection System ◽  
Fabric Defect Detection ◽  
Latent Space ◽  
Variational Autoencoder ◽  
Fabric Defect ◽  
Fabric Surface

Defective products are a major contributor toward a decline in profits in textile industries. Hence, there are compelling needs for an automated inspection system to identify and locate defects on the fabric surface. Although much effort has been made by researchers worldwide, there are still challenges with computation and accuracy in the location of defects. In this paper, we propose a hybrid semi-supervised method for fabric defect detection based on variational autoencoder (VAE) and Gaussian mixture model (GMM). The VAE model is trained for feature extraction and image reconstruction while the GMM is used to perform density estimation. By synthesizing the detection results from both image content and latent space, the method can construct defect region boundaries more accurately, which are useful in fabric quality evaluation. The proposed method is validated on AITEX and DAGM 2007 public database. Results demonstrate that the method is qualified for automated detection and outperforms other selected methods in terms of overall performance.

scholarly journals New Physics Agnostic Selections For New Physics Searches

2020 ◽  
Vol 245 ◽  
pp. 06039
Author(s):  
Kinga Anna Woźniak ◽  
Olmo Cerri ◽  
Javier M. Duarte ◽  
Torsten Möller ◽  
Jennifer Ngadiuba ◽  
...  
Keyword(s):  
Anomaly Detection ◽  
Input Data ◽  
Control Sample ◽  
Detection Algorithm ◽  
New Physics ◽  
Original Dataset ◽  
Variational Autoencoder ◽  
Unsupervised Anomaly Detection ◽  
Input Event ◽  
Model Independent

We discuss a model-independent strategy for boosting new physics searches with the help of an unsupervised anomaly detection algorithm. Prior to a search, each input event is preprocessed by the algorithm - a variational autoencoder (VAE). Based on the loss assigned to each event, input data can be split into a background control sample and a signal enriched sample. Following this strategy, one can enhance the sensitivity to new physics with no assumption on the underlying new physics signature. Our results show that a typical BSM search on the signal enriched group is more sensitive than an equivalent search on the original dataset.

scholarly journals Comparing weak- and unsupervised methods for resonant anomaly detection

2021 ◽  
Vol 81 (7) ◽  
Author(s):  
Jack H. Collins ◽  
Pablo Martín-Ramiro ◽  
Benjamin Nachman ◽  
David Shih
Keyword(s):  
Large Hadron Collider ◽  
Anomaly Detection ◽  
Cross Sections ◽  
Hadron Collider ◽  
New Physics ◽  
Classification Performance ◽  
Detection Techniques ◽  
Resonance Search ◽  
Weakly Supervised ◽  
Physics Signal

AbstractAnomaly detection techniques are growing in importance at the Large Hadron Collider (LHC), motivated by the increasing need to search for new physics in a model-agnostic way. In this work, we provide a detailed comparative study between a well-studied unsupervised method called the autoencoder (AE) and a weakly-supervised approach based on the Classification Without Labels (CWoLa) technique. We examine the ability of the two methods to identify a new physics signal at different cross sections in a fully hadronic resonance search. By construction, the AE classification performance is independent of the amount of injected signal. In contrast, the CWoLa performance improves with increasing signal abundance. When integrating these approaches with a complete background estimate, we find that the two methods have complementary sensitivity. In particular, CWoLa is effective at finding diverse and moderately rare signals while the AE can provide sensitivity to very rare signals, but only with certain topologies. We therefore demonstrate that both techniques are complementary and can be used together for anomaly detection at the LHC.

scholarly journals Determining the lifetime of long-lived particles at the HL-LHC

2021 ◽  
Vol 81 (2) ◽  
Author(s):  
Shankha Banerjee ◽  
Biplob Bhattacherjee ◽  
Andreas Goudelis ◽  
Björn Herrmann ◽  
Dipan Sengupta ◽  
...  
Keyword(s):  
Hadron Collider ◽  
New Physics ◽  
Final States ◽  
Missing Energy ◽  
Lifetime Estimation ◽  
Timing Information ◽  
Pile Up ◽  
Important Addition ◽  
Model Independent ◽  
The Mean

AbstractWe examine the capacity of the Large Hadron Collider to determine the mean proper lifetime of long-lived particles assuming different decay final states. We mostly concentrate on the high luminosity runs of the LHC, and therefore, develop our discussion in light of the high amount of pile-up and the various upgrades for the HL-LHC runs. We employ model-dependent and model-independent methods in order to reconstruct the proper lifetime of neutral long-lived particles decaying into displaced leptons, potentially accompanied by missing energy, as well as charged long-lived particles decaying ihnto leptons and missing energy. We also present a discussion for lifetime estimation of neutral long-lived particles decaying into displaced jets, along with the challenges in the high PU environment of HL-LHC. After a general discussion, we illustrate and discuss these methods using several new physics models. We conclude that the lifetime can indeed be reconstructed in many concrete cases. Finally, we discuss to which extent including timing information, which is an important addition in the Phase-II upgrade of CMS, can improve such an analysis.

scholarly journals Disentangling QCD and new physics in D → πℓ+ℓ−

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Aoife Bharucha ◽  
Diogo Boito ◽  
Cédric Méaux
Keyword(s):  
Standard Model ◽  
Branching Ratio ◽  
Branching Ratios ◽  
New Physics ◽  
Operator Product ◽  
Beyond The Standard Model ◽  
Spectral Functions ◽  
The Standard Model ◽  
Model Independent ◽  
Weak Annihilation

Abstract In this paper we consider the decay D+ → π+ℓ+ℓ−, addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low q2 and at high q2, adapting the existing calculation for B decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using e+e− → (hadrons) and τ → (hadrons) + ντ data as well as the branching ratios for the resonant decays D+ → π+R(R → ℓ+ℓ−), with R = ρ, ω, and ϕ. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of q2. Focusing then on the observables FH and AFB, we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

scholarly journals Anomaly detection with convolutional Graph Neural Networks

2021 ◽  
Vol 2021 (8) ◽  
Author(s):  
Oliver Atkinson ◽  
Akanksha Bhardwaj ◽  
Christoph Englert ◽  
Vishal S. Ngairangbam ◽  
Michael Spannowsky
Keyword(s):  
Neural Networks ◽  
Anomaly Detection ◽  
Top Quarks ◽  
New Physics ◽  
Broad Applicability ◽  
Latent Space ◽  
Edge Features ◽  
Graph Neural Networks ◽  
Promising Avenue ◽  
Do So

Abstract We devise an autoencoder based strategy to facilitate anomaly detection for boosted jets, employing Graph Neural Networks (GNNs) to do so. To overcome known limitations of GNN autoencoders, we design a symmetric decoder capable of simultaneously reconstructing edge features and node features. Focusing on latent space based discriminators, we find that such setups provide a promising avenue to isolate new physics and competing SM signatures from sensitivity-limiting QCD jet contributions. We demonstrate the flexibility and broad applicability of this approach using examples of W bosons, top quarks, and exotic hadronically-decaying exotic scalar bosons.

SEARCH FOR NEW PHYSICS IN eμX DATA AT THE TEVATRON USING SLEUTH: A QUASI-MODEL-INDEPENDENT SEARCH STRATEGY FOR NEW PHYSICS

2001 ◽  
Vol 16 (supp01b) ◽  
pp. 888-890
Author(s):  
◽  
BRUCE KNUTESON
Keyword(s):  
Standard Model ◽  
Search Strategy ◽  
New Physics ◽  
Beyond The Standard Model ◽  
Final States ◽  
Final State ◽  
The Standard Model ◽  
Model Independent

We present a quasi-model-independent search for physics beyond the standard model. We define final states to be studied, and construct a rule that identifies a set of variables appropriate for any particular final state. A new algorithm ("Sleuth") searches for regions of excess in the space of those variables and quantifies the significance of any detected excess. After demonstrating the sensititvity of the method, we apply it to the semi-inclusive channel eμX collected in ≈108 pb -1 of [Formula: see text] collisions at [Formula: see text] at the DØ experiment at the Fermilab Tevatron. We find no evidence of new high pT physics in this sample.

scholarly journals Non-standard interactions in SMEFT confronted with terrestrial neutrino experiments

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Yong Du ◽  
Hao-Lin Li ◽  
Jian Tang ◽  
Sampsa Vihonen ◽  
Jiang-Hao Yu
Keyword(s):  
Neutrino Oscillation ◽  
New Physics ◽  
Effective Field ◽  
Scalar Leptoquark ◽  
Double Chooz ◽  
The Standard Model ◽  
Reactor Neutrino ◽  
Model Independent ◽  
Neutrino Experiments ◽  
Individual Dimension

Abstract The Standard Model Effective Field Theory (SMEFT) provides a systematic and model-independent framework to study neutrino non-standard interactions (NSIs). We study the constraining power of the on-going neutrino oscillation experiments T2K, NOνA, Daya Bay, Double Chooz and RENO in the SMEFT framework. A full consideration of matching is provided between different effective field theories and the renormalization group running at different scales, filling the gap between the low-energy neutrino oscillation experiments and SMEFT at the UV scale. We first illustrate our method with a top- down approach in a simplified scalar leptoquark model, showing more stringent constraints from the neutrino oscillation experiments compared to collider studies. We then provide a bottom-up study on individual dimension-6 SMEFT operators and find NSIs in neutrino experiments already sensitive to new physics at ∼20 TeV when the Wilson coefficients are fixed at unity. We also investigate the correlation among multiple operators at the UV scale and find it could change the constraints on SMEFT operators by several orders of magnitude compared with when only one operator is considered. Furthermore, we find that accelerator and reactor neutrino experiments are sensitive to different SMEFT operators, which highlights the complementarity of the two experiment types.

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