NA62: Hidden Sector Physics

Modern experimental physics is often probing for new physics by either finding deviations from predictions on extremely precise measurements, or by looking for a new signal that cannot be explained with existing models. The NA62 experiment at CERN does the former by measuring the ultra-rare decay $K^+ \rightarrow \pi^+ \nu \bar \nu$. However, due to the layout of the experiment and the high beam energy, there is also an excellent opportunity to search for completely new physics in a hidden sector. Two potential dark matter mediators are of particular interest: axion-like particles (ALPs) and dark photons. The detection of these particles will be direct by assuming visible decay modes, namely ALPs with diphoton decay and dark photons to a dilepton final state. The work done this summer has been devoted to understanding several backgrounds in the hidden sector search at NA62. This document is provided to facilitate future endeavors of similar nature in background analysis.