Reading aloud A Russian research team from the Budker Institute for Nuclear Physics (BINP) in Novosibirsk has for the first time observed the collapse of a high-energy photon into two low-energy photons. The extremely rare decay can take place in the electric fields of atoms and was predicted decades ago by quantum field theory. This is reported in the journal Physical Review Letters (volume 89 reference number 061802). The nuclear physicists around Alexander Milstein shot in their experiment high-energy gamma rays on a crystal of bismuth germanate. The electric field of the crystal atoms excited an extremely small fraction of the atoms traversing the crystal to decay into two low-energy photons. Of the 1.6 billion photons striking the detectors behind the crystal, only about four hundred had an energy balance suggestive of decay.

The decay of the gamma photons takes place via an intermediate step, in which a photon first decays into a virtual electron-positron pair. However, this pair does not subsequently burn itself into a photon of the same energy as the original photon? rather, one of the two particle partners first releases a photon of low energy before the two particles are blasted into another photon.

This effect predicted by quantum field theory can take place in the strong electric fields of atoms. Physicists have long been convinced of the existence of photon decay? however, its detection is enormously difficult. As early as 1995, the Russian team had presented initial evidence of successful decay at several conferences, but the exact data analysis took almost seven years.

The photon decay described here is not to be confused with the so-called parametric decay of photons, in which an energetic photon decays into two infrared photons in a nonlinear crystal. Rather, it is an example of the interaction of a virtual particle pair with the electric field of an atom. Fortunately, the outcome of the experiment is exactly in line with the predictions of quantum field theory. Researchers believe that their work should encourage peers to demonstrate other fundamental but not yet experimentally observed predictions of quantum field theory. display

Stefan Maier


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