Toward Model-Agnostic Detection of New Physics Using Data-Driven Signal Regions

TL;DR

This paper introduces a model-agnostic, data-driven method for detecting new physics signals by identifying regions in high-dimensional data space most affected by potential signals, without relying on prior domain knowledge.

Contribution

It proposes a novel approach using a low-pass filter concept and density ratio estimation to find signal-enriched regions in high-dimensional data, applicable to unknown new physics signals.

Findings

Successfully applied to simulated HH → 4b events

Efficiently identifies signal-rich regions in high-dimensional space

Does not require prior knowledge of signal characteristics

Abstract

In the search for new particles in high-energy physics, it is crucial to select the Signal Region (SR) in such a way that it is enriched with signal events if they are present. While most existing search methods set the region relying on prior domain knowledge, it may be unavailable for a completely novel particle that falls outside the current scope of understanding. We address this issue by proposing a method built upon a model-agnostic but often realistic assumption about the localized topology of the signal events, in which they are concentrated in a certain area of the feature space. Considering the signal component as a localized high-frequency feature, our approach employs the notion of a low-pass filter. We define the SR as an area which is most affected when the observed events are smeared with additive random noise. We overcome challenges in density estimation in the high-dimensional feature space by learning the density ratio of events that potentially include a signal to the complementary observation of events that closely resemble the target events but are free of any signals. By applying our method to simulated $\mathrm{HH} \rightarrow 4b$ events, we demonstrate that the method can efficiently identify a data-driven SR in a high-dimensional feature space in which a high portion of signal events concentrate.