The Physics of Hanbury Brown-Twiss Intensity Interferometry: From Stars to Nuclear Collisions

Author

• Gordon Baym
  • Department of Physics, University of Illinois at Urbana-Champaign

Overview

• Hanbury Brown-Twiss (HBT) interferometry was developed in the 1950s to measure angular sizes of astronomical objects using correlations of signal intensities.
• It revealed quantum bunching of photons, contributing to quantum optics.
• The technique is applied in high-energy nuclear and particle collisions to study space-time geometry and wave mechanics of particles.

Introduction to HBT

• HBT measures two identical particle correlations in particle and heavy-ion collisions.
• Provides insights into the geometry of the collision volume.
• Illustrated with correlation functions for particle collisions.
  • Data from NA44 and E877 experiments.

Physics of HBT Interferometry

• Relies on intensity rather than amplitude comparison.
• Measures correlations between intensities in independent detectors.
• Applies to both astronomical and high-energy physics contexts, with variations in application.
  • Quantum mechanics play a critical role.

Historical Context

• Developed post-WWII, leveraging radar technology.
• Enabled measurement of radio star sizes.
• Transitioned from classical to quantum understanding.
• Demonstrated with tabletop experiments showing photon bunching.

Basic Model of HBT

• Differentiates from amplitude interferometry by correlating intensity at different points.
• Uses a model with two random point sources and two detectors to explain principles.
• Correlation functions are Fourier transforms of source distributions.
• Important distinctions between astronomical and high-energy applications.

Quantum Mechanics of HBT

• Quantum mechanics explains the correlation of particles as a result of wave mechanics.
• Involves multiparticle correlations sensitive to wave function symmetries.
• Provides insights into wave packets and detection processes.

Detector Response and Secondary Scattering

• Describes how particles in wave packet states are detected.
• Secondary scattering effects in targets and media like air affect measurements.
• Corrections necessary for accurate interpretation.

Applications and Challenges

• Expanded to atomic and condensed matter physics.
• Challenges include Coulomb interactions, coherence, and scattering effects.
• Accurate interpretation requires understanding various uncertainties.

Conclusion

• HBT interferometry remains a valuable tool across multiple physics domains.
• Ongoing research to refine techniques and address challenges in interpretation.