Detecting anomalous quartic gauge couplings using the isolation forest machine learning algorithm

Aug 5, 2026

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Searches for new physics beyond the Standard Model rely on finding rare events with kinematical differences. This work applies the isolation forest (IF) algorithm in a model-independent way to pick out kinematically unusual events associated with anomalous quartic gauge couplings (aQGCs). The method is efficient at identifying signal-like events and can further constrain the aQGC coefficients, highlighting strong prospects for future new-physics studies.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages19

Reading Time48 min

AccessFree to download

Introduction

A brief introduction of isolation forest

Application to detecting aQGC signals

Summary

View metadata, citation and similar [papers at ](papers at core.ac.uk)[core.ac.uk](papers at core.ac.uk) brought to you by CORE [provided by](provided by arXiv.org)[ arXiv.org](provided by arXiv.org) e-Print Archive arXiv :2103 .03151v1 [hep-ph] 4 Mar 2021 Detect anomalous quartic gauge couplings using isolation forest Yu-Chen Guo,􀀃 Li Jiang,† and Ji-Chong Yang‡ Department of Physics, Liaoning Normal University, Dalian 116029, China Abstract The search of new physics (NP) beyond the Standard Model is one of the most important tasks of high energy physics. A common characteristic of the NP signals is that they are usually few and kinematically di􀀋erent. We use a model independent strategy to study the phenomenology of NP by directly picking out and studying the kinematically unusual events. For this purpose, the isolation forest (IF) algorithm is applied, which is found to be e􀀎cient in identifying the signal events of the anomalous quartic gauge couplings (aQGCs) . The IF algorithm can also be used to constraint the coe􀀎cients of aQGCs. As a machine learning algorithm, the IF algorithm shows a good prospect in the future studies of NP. 􀀃 Electronic address: [ycguo@lnnu.edu.cn](ycguo@lnnu.edu.cn) †Electronic address: [847495612@qq.com](847495612@qq.com) ‡Electronic address: [yangjichong@lnnu.edu.cn](yangjichong@lnnu.edu.cn) I. INTRODUCTION Despite the great success of the Standard Model (SM), there are still many unanswered questions making the search for new physics (NP) beyond the SM a very important issue [1] . Except for a few cases that are known or suspected to deviate from the SM [2], in most cases, the experiments are in good agreement with the SM. The searching of NP is to look for a small number of anomalies in the vast amount of experimental data. Meanwhile, the kinematic features of the events induced by NP are usually di􀀋erent from the SM, which is the reason that event selection strategies (ESSs) are commonly applied in the phenomenological studies of NP. From the perspective of the SM e􀀋ective theory (SMEFT) [3], that is because the signals are induced by new interactions di􀀋erent from the SM. It follows that the search of NP is to search the events which are ‘few and kinematically di􀀋erent’. In this paper, we make use of the above features of NP and use a model independent strategy to directly search for kinematically unusual events. This strategy has the advantage that it can be applied generally. Taking the SMEFT for example, which is also a model independent way to search for the NP signals. For one generation of fermions, there are 895 baryon number conserving dimension-8 operators [4, 5], and kinematic analysis needs to be done for each operator. Compared with the SMEFT, our strategy is independent of the operators. Except for that, unlike the search of NP ina process which may turn out to be a wasted e􀀋ort, the kinematically unusual events are always worth attention even if they are not from NP. They could be faults in the experiments, or could be the rare processes allowed by the SM. As an example, we use our strategy to study the anomalous quartic gauge couplings (aQGCs) [6], which are modi􀀌cations to the SM gauge interactions intensively studied [4, 7–9] . aQGCs can be contributed by a lot of NP models such as Born-Infeld theory, composite Higgs, warped extra dimensions, two Higgs doublet models, U(1)L􀀖􀀀L􀀜 , andaxion-like particles [10, 11] . Since dimension-6 operators cannot contribute to aQGCs independently [4], we concentrate on the dimension-8 operators. A recent study shows that the dimension-8 operators are important in the convex geometry point of view to the SMEFT space [12] . Besides, there are cases sensitive to dimension-8 operators because the contributions from dimension-6 operators are absent [10, 13, 14] . In the case of anomalous gauge couplings, aQGCs can lead to richer helicity combinations than dimension-6 anomalous tri- linear gauge couplings (aTGCs) [1

FAQs

Why does the paper focus on “few and kinematically different” events in new physics searches?

New-physics signals are typically rare and exhibit kinematics distinct from the Standard Model, motivating event-selection strategies centered on unusual event properties.

How does the isolation forest (IF) algorithm help detect anomalous quartic gauge couplings (aQGCs)?

IF identifies points that are few and far from the others, enabling it to act like an automatic event-selection strategy that can isolate signal-like events for aQGCs.

Can the IF algorithm be used beyond event detection?

Yes. The approach can also constrain the coefficients of aQGCs, linking anomaly detection outputs to parameter inference for new-physics scenarios.

Aug 5, 2026

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