# Machine learning classification: case of Higgs boson CP state in H to tau tau decay at LHC

## TL;DR

This paper investigates the use of various machine learning techniques, including deep neural networks, to classify the CP state of the Higgs boson in tau decay channels at the LHC, emphasizing the impact of neutrino constraints on classification sensitivity.

## Contribution

It demonstrates that incorporating constraints on neutrinos significantly improves ML-based classification of Higgs CP states, comparing multiple ML methods for this task.

## Key findings

- Neutrino constraints enhance classification sensitivity.
- Deep Neural Networks outperform other ML methods.
- ML techniques can effectively distinguish Higgs CP states.

## Abstract

Machine Learning (ML) techniques are rapidly finding a place among the methods of High Energy Physics data analysis. Different approaches are explored concerning how much effort should be put into building high-level variables based on physics insight into the problem, and when it is enough to rely on low-level ones, allowing ML methods to find patterns without explicit physics model. In this paper we continue the discussion of previous publications on the CP state of the Higgs boson measurement of the H to tau tau decay channel with the consecutive tau^pm to rho^pm nu; rho^pm to pi^pm pi^0 and tau^pm to a_1^pm nu; a_1^pm to rho^0 pi^pm to 3 pi^pm cascade decays. The discrimination of the Higgs boson CP state is studied as a binary classification problem between CP-even (scalar) and CP-odd (pseudoscalar), using Deep Neural Network (DNN). Improvements on the classification from the constraints on directly non-measurable outgoing neutrinos are discussed. We find, that once added, they enhance the sensitivity sizably, even if only imperfect information is provided. In addition to DNN we also evaluate and compare other ML methods: Boosted Trees (BT), Random Forest (RF) and Support Vector Machine (SVN).