EMC effect
The EMC effect in nuclear and particle physics is the dependence of the structure functions of the nucleons on the nuclear environment. The structure functions describe the momentum distribution of the quarks from which the nucleons are built. It was named after the European Muon Collaboration (EMC) , which discovered it at CERN in 1983 .
With the deep inelastic scattering of electrons , muons or neutrinos by protons and neutrons, their structural functions are measured, which in turn provide information about their internal structure. Since this happens at very high energy and momentum transfers, far higher than the binding energy of atomic nuclei, it was expected that it does not matter whether these particles are free or part of atomic nuclei - apart from kinematic effects due to the Fermi movement . In fact, however, there was a significant deviation, in the range of small pulse fractions up to −20%.
There are different approaches to explain this effect: the interaction of quarks across nucleon boundaries, partial absorption of the interacting virtual photon ( nuclear shadowing ) through its fluctuation in virtual hadrons, formation of multi-quark clusters and others. A generally accepted explanation is still pending.
literature
- B. Povh , K. Rith , Ch. Scholz, F. Zetsche, W. Rodejohann: Particles and nuclei - an introduction to physical concepts . 9th edition. SpringerSpectrum, Berlin 2013, ISBN 978-3-642-37821-8 , pp. 118-121 .
Individual evidence
- ^ JJ Aubert u. a .: The ratio of the nucleon structure functions F2N for iron and deuterium, Phys. Lett. B, Vol. 123, 1983, pp. 275-278.
- ↑ The EMC effect still puzzles after 30 years. CERN, April 26, 2013, accessed January 31, 2014 .