On the CP Nature of the `95 GeV' Anomalies

TL;DR

This paper investigates whether the 95 GeV anomalies observed at LEP and LHC are due to a new spin-0 particle and determines its CP nature using $ au^+ au^-$ decay data, with implications for future HL-LHC measurements.

Contribution

It introduces a model-independent method to determine the CP properties of a potential new particle at the LHC using $ au^+ au^-$ decays, and assesses HL-LHC's capability to distinguish CP states.

Findings

HL-LHC can determine the CP nature within $ heta ightarrow ext{(0.27-0.47 radians)}$ at 90% CL.

The method is model-independent and applicable to various BSM hypotheses.

The analysis demonstrates the potential to clarify the CP quantum numbers of the 95 GeV anomaly.

Abstract

Under the assumption that the various evidences of a `95 GeV' excess, seen in data at the Large Electron Positron (LEP) collider as well as the Large Hadron Collider (LHC), correspond to actual signals of new physics Beyond the Standard Model (BSM), we characterise the underlying particle explaining these anomalies in terms of its Charge/Parity (CP) quantum numbers. In doing so, we use $\chi^2$ fits to test the CP-even (scalar) and CP-odd (pseudoscalar) hypotheses and superpositions of these, thus under the assumption of a spin-0 resonance. This is done through the exploitation of $\tau^+\tau^-$ decays, in both their fully hadronic and semi-leptonic modes, in a model-independent way, so that our approach enables one to test a variety of BSM hypotheses, having proven here that the High-Luminosity LHC (HL-LHC) will be in a position to disentangle the CP nature of such a new particle within $\pm(0.27-0.47)$ radians of the true hypothesis at $90\%$ Confidence Level (CL), depending on the assumed background systematics.