Probing a light long-lived pseudo-scalar from Higgs decay via displaced taus at the LHC

TL;DR

This paper explores the detection of a light, long-lived pseudoscalar particle produced in Higgs decays at the LHC, focusing on displaced tau signatures to identify potential new physics beyond the Standard Model.

Contribution

It provides a detailed simulation study of Higgs decays into a long-lived pseudoscalar within the aligned 2HDM, highlighting the detectability of displaced tau vertices at the LHC.

Findings

Signal detectable at 300 fb$^{-1}$ luminosity

Displaced tau vertices can serve as a signature for new physics

Benchmark points demonstrate the model's testability at the LHC

Abstract

A light (GeV mass) long-lived ($c\tau$ around dozens of millimeters) CP-odd scalar can be readily predicted in new physics models. In this work we investigate the Higgs decay into such a light scalar plus a $Z$-boson and take the aligned two-Higgs-doublet model (2HDM) as an example. This light long-lived scalar, with the dominant decay to tau leptons, will fly over a distance from the production point and present a displaced vertex in an Inner Detector of a generally purposed experiment like ATLAS or CMS. In our study we focus on the LHC experiment and perform Monte Carlo simulations for the signal and backgrounds. We demonstrate some benchmark points for the aligned 2HDM and find the signal to be detectable when the luminosity is accumulated to 300 fb$^{-1}$. So our study suggests an experimental search for this process in the ongoing LHC.