Simulation of dark photon sensitivity in $\eta \rightarrow \gamma e^+e^-$ at HIAF

TL;DR

This study simulates the potential to detect dark photons through eta meson decays at a proposed HIAF experiment, utilizing a silicon-pixel spectrometer and extensive data collection to improve sensitivity and set limits on dark photon parameters.

Contribution

It introduces a detailed simulation framework for dark photon detection in eta decays at HIAF, including spectrometer design, background estimation, and sensitivity analysis.

Findings

Estimated eta sample size of 5.9 x 10^11 for one month of data collection.

Designed a silicon-pixel spectrometer with evaluated efficiency and resolution.

Projected upper limits on dark photon branching ratios and model parameters.

Abstract

We present a simulation study of dark photon sensitivity in a suggested $\eta$ factory experiment at Huizhou. The vast number of $\eta$ mesons are produced by bombarding the high-intensity HIAF proton beam on a multi-layer target of light nucleus. The kinematic energy of the beam is at 1.8 GeV. For a prior experiment of one-month running, about $5.9 \times 10^{11}$ $\eta$ samples would be collected, providing substantial data for a sound statistical analysis. A compact spectrometer based on the full silicon-pixel tracker is conceptually designed for the detection of the final-state particles. The GiBUU event generator is utilized for the background estimation without the dark photon signal. A spectrometer simulation package ChnsRoot is constructed for evaluating the spectrometer performances in searching the dark photon in $\eta$ rare decay. The efficiency and resolutions of $\eta \rightarrow \gamma e^+e^-$ decay channel are studied in detail. The branching-ratio upper limit of dark photon in $\eta \rightarrow \gamma e^+e^-$ decay and the sensitivity to the model parameter are given from the simulations.