Detection of dark photons generated by muons\' bremsstrahlung in the COSINE-100 experiment

Author(s)

David Fernando Freitas da Silva Cavalcante

• Document type: Master's Dissertation
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Física (IF/SBI)
• Defense date: 2024-09-10

Examining board members

Nelson Carlin Filho; Mauro Rogerio Cosentino; Carlos Frajuca

• Advisor: Nelson Carlin Filho

Abstract

The existence of dark matter is supported by abundant evidence from astrophysical observations, which primarily involve gravitational phenomena. Consequently, the only known interaction between dark matter and baryonic matter is gravitational, necessitating exploration of all other possible types of interactions to fully understand its nature. Various theories have been proposed to describe dark matter particle properties, with experiments designed to test them. For some time, the most widely accepted theory within the scientific community has been that of Weakly Interacting Massive Particles (WIMPs), though numerous experiments searching for them have not yielded conclusive results. This has spurred the search for other candidate particles such as dark photons and axions, prominent models of bosonic dark matter. Research into these models is expanding, aided by newer technologies enhancing detector sensitivity, potentially providing constraints more precise than those from astrophysical observations. One such experiment is COSINE-100, located in the Yangyang underground laboratory in South Korea. Operational since 2016, it employs 106 kg of NaI(Tl) crystals as its primary detectors. A major challenge for such experiments is distinguishing sought-after events from background signals, particularly muon signals, which are abundant in cosmic rays. However, there exists a model predicting kinetic coupling between muons and dark photons, detectable either directly or indirectly if the muon undergoes bremsstrahlung in a target material. Although initially designed to search for annual modulation of dark matter, COSINE-100 possesses capabilities to detect excess events in its detectors, potentially testing this dark photon model. This study aims to analyze COSINE-100 data specifically for events caused by dark photons generated via muon bremsstrahlung, given the great abundance of muons at Earth\'s surface. Five detection possibilities were explored: direct detection, Compton-like scattering and absorption, and indirect detection via decay into 3 photons (for masses lower than 2m_e ), decay into electron-positron pairs (for masses greater than 2m_e ), and photon oscillation (also for masses lower than 2m_e ). It was found that considering the flux of dark photons produced across Earth\'s surface, a maximum of 10^(-5) detectable events per day per keV deposited in NaI(Tl) crystals per kg of their mass is expected. Furthermore, it was estimated that more than 1 detectable event per year should occur for masses between 10 keV and 1 MeV, and coupling parameters between 10^(-4) and 10^(-2) . Finally, the analysis of the experimental data (from COSINE-100 SET3) in single hit (up to 100 keV) in the crystals showed that the calculated detection spectra with the largest amplitudes are between 10^5 and 10^6 times smaller than that needed to generate a signal, with 90% C.L. In short, these estimates do not provide good prospects for detecting excess events. However, analyses of multiple hit events can be done in an attempt to constrain the dark photon parameter space, if the amplitude of the calculated spectra is large enough (relative to the present background) for higher energies. (AU)

• FAPESP's process: 22/12002-7 - Detection of dark photons generated by muons' Bremsstrahlung in the COSINE-100 experiment
• Grantee: David Fernando Freitas da Silva Cavalcante
• Support Opportunities: Scholarships in Brazil - Master