Hanbury Brown and Twiss effect

In physics, the Hanbury Brown and Twiss (HBT) effect is any of a variety of correlation and anti-correlation effects in the intensities received by two detectors from a beam of particles. HBT effects can generally be attributed to the dual Wave–particle duality nature of the beam, and the results of a given experiment depend on whether the beam is composed of fermions or bosons. Devices which use the effect are commonly called intensity interferometers and were originally used in astronomy, although they are also heavily used in the field of quantum optics.

In 1956, Robert Hanbury Brown and Richard Q. Twiss published A test of a new type of stellar interferometer on Sirius, in which two photomultiplier tubes (PMTs), separated by about 6 meters, were aimed at the star Sirius. Light collected into the PMTs using mirrors from searchlights. An interference effect was observed between the two intensities, revealing a positive correlation between the two signals, despite the fact that no phase information was collected. Hanbury Brown and Twiss used the interference signal to determine the apparent angular size of Sirius, claiming excellent resolution.

Also, in the field of particle physics, Goldhaber et al. performed an experiment in 1959 in Berkeley and found an unexpected angular correlation among identical pions, discovering the ρ⁰ resonance, by means of ${\displaystyle \rho ^{0}\rightarrow \pi ^{-}\pi ^{+}}$ decay. From then on, the HBT technique started to be used by the heavy-ion community to determine the space-time dimensions of the particle emission source for heavy ion collisions. For recent developments in this field, cf. for example the review article by Lisa.

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