Performance characterization of the transition-edge sensor array, readout system, and optical coupling of the Simons...

Area of Science:

• Cosmology and astrophysics
• Instrumental science

Background:

• High-sensitivity cosmic microwave background (CMB) polarization measurements are crucial for cosmology and early universe physics.
• The Simons Array experiment aims to observe CMB polarization using advanced detectors in Chile.

Purpose of the Study:

• To characterize the on-sky sensitivity of the Simons Array detectors (polarbear-2a and polarbear-2b).
• To compare achieved sensitivity with predictions based on detector, readout, and optical properties.

Main Methods:

• Characterization of detector properties to model transition-edge sensor (TES) responsivity.
• Estimation of receiver optical throughput and readout noise contributions.
• Frequency-domain multiplexing readout for thousands of cryogenic detectors.

Main Results:

• On-sky noise equivalent temperature was higher than the design goal.
• Lower optical throughput and elevated readout noise were identified as primary causes.
• polarbear-2b showed degraded performance, possibly due to radio frequency interference.

Conclusions:

• The performance of polarbear-2a can be predicted using an updated sensitivity model.
• The methods are applicable to characterizing other instruments with TES arrays and frequency-domain multiplexing.