Perpustakaan Digital ITB

Number of astronomical observations suggest that the dominant matter in the universe is non-baryonic dark matter. However, the searches for dark matter has been one of the most challenging research topics in physics. Weakly Interacting Massive Particles (WIMPs) are promising candidates of dark matter, supporting by many astronomical considerations and theoretical predictions. Many of direct dark matter experiments are looking for WIMP dark matter by using various detection techniques and technologies. But one exceptional, DAMA group reported over 20 years of annual modulation signal using NaI(Tl) crystal scintillation detectors. They claim that this signal is WIMP-like signal in their detectors. However, no experiments can prove the signal with set limits which are incompatible with DAMA result. An experiment is needed with same target material detector to resolve both result without conflict. COSINE-100 is a joint effort experiment by the KIMS-NaI (Korean Invisible Mass Search) and the DM-Ice with a goal to reproduce or refute the annual modulation signature reported by DAMA group using Thallium-doped Sodium Iodide crystal scintillations. COSINE-100 experiment is operating and located at the Yangyang Underground Laboratory (Y2L) in South Korea. The construction and assembly process was completed in the Summer of 2016 and the detector is currently collecting physics data. During the operation, several things needed to be considered are backgrounds level including from the cosmic-ray showers. In rare event searches, cosmic-ray muons can produce seasonal modulation of event which could mimic weakly interacting massive particle (WIMP) signal in nuclear recoils. DAMA group did not have muon tag system that they did not study cosmic-ray seasonal modulation effect. To tag the muon-events and study the correlations between muon and crystal-events, COSINE-100 has installed the muon detectors in the outside shielding structure. An array of 3-cm thick plastic scintillator panels surrounds the crystal detector in all sides. This work focuses on the design, construction and assembly process, data analysis of the COSINE-100 detector, with particular emphasis on muon-modulation. Muons, identified by a selection criteria, are developed with a coincidence technique and time difference between two panels. A coincidence and threshold are used to remove gamma-backgrounds at low energy and showed the muon-like events in high energy region. The threshold is set to be different for each side detector. A time difference cut has been developed to reduce fake-event in signal area. The muon coincident signal should be in close time-range of the gap. The time correlation observed for the muon candidate events, a signal range of -100ns < DT < 115ns. Considering the background distribution, the background contamination in the signal region is calculated to be 0.3 %. Furthermore, the muon selection efficiency was estimated to be 99.9 ± 0.1 % when the charge threshold cuts are applied. A similar muon selection technique is applied for all pairs of different sides to tag muon candidate events. Muon events were found with direct or prompt energy deposition > 4 MeV. Muons can also induce low energy phosphorescence event in crystals which can mimic WIMP signal with a confined modulation signature. An event selection for crystal study has been used by rejecting 30 ms from a muon hit in plastic scintillator. It gives approximately 0.1 % deadtime for data taking in the detector. This rejection is used in crystal analysis to prevent large number of accidental events. With 2 years of physics data, an annual modulation behaviour has been observed with an amplitude of (0.51 ± 0.24) % and a phase of (182 ± 25) d corresponding to a maximum on the 30th of June Using the atmospheric temperature data, we studied the correlation between muon and temperature modulation with a positive correlation. With an effective coefficient alpha_{T} = 0.815 ± 0.097. This result represents the study of the muon flux modulation for Y2L site and is in good agreement with theoretically expectations.