Probing primordial gravitational waves: Ali CMB Polarization Telescope

Area of Science:

• Cosmology and astrophysics
• Particle physics
• Gravitational wave astronomy

Background:

• The Cosmic Microwave Background (CMB) holds crucial information about the early universe.
• Detecting primordial gravitational waves (PGWs) is a key goal in modern cosmology.
• China's Gravitational-wave Program seeks to advance gravitational wave research.

Purpose of the Study:

• Introduce the Ali CMB Polarization Telescope (AliCPT) project, a Sino-US collaboration.
• Detail the scientific objectives, focusing on probing PGWs and testing CPT symmetry.
• Describe the two-stage development plan for the AliCPT observatory.

Main Methods:

• Construction of the AliCPT-1 observatory at 5250m in Tibet, the world's highest ground-based CMB observatory.
• Utilizing approximately 7000 transition-edge sensor detectors operating at 95 GHz and 150 GHz for AliCPT-1.
• Planning for a more sensitive AliCPT-2 with over 20,000 detectors.

Main Results:

• Simulations indicate AliCPT will enhance the constraint on the tensor-to-scalar ratio (r) by an order of magnitude within three years.
• The project will enable precise measurements of the CMB rotation angle.
• A two-order-of-magnitude improvement in the limit for CPT symmetry testing is projected with three years of observation.

Conclusions:

• AliCPT represents a significant advancement in CMB polarization experiments.
• The observatory will provide unprecedented data for understanding the early universe and fundamental physics.
• It opens new avenues for cosmological research from the Northern Hemisphere.