high-energy physics Particle physics or high-energy physics is the study of fundamental particles and forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the scale of protons and neutrons, while the stu ...

, the Landau–Pomeranchuk–Migdal effect, also known as the Landau–Pomeranchuk effect and the Pomeranchuk effect, or simply LPM effect, is a reduction of the bremsstrahlung and

pair production Pair production is the creation of a subatomic particle and its antiparticle from a neutral boson. Examples include creating an electron and a positron, a muon and an antimuon, or a proton and an antiproton. Pair production often refers ...

cross sections at high energies or high matter densities. It is named in honor of

Lev Landau Lev Davidovich Landau (; 22 January 1908 – 1 April 1968) was a Soviet physicist who made fundamental contributions to many areas of theoretical physics. He was considered as one of the last scientists who were universally well-versed and ma ...

, Isaak Pomeranchuk and Arkady Migdal.

Overview

A high energy particle undergoing multiple soft scatterings from a medium will experience interference effects between adjacent

scattering In physics, scattering is a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiat ...

sites. From uncertainty as the longitudinal momentum transfer gets small the particles wavelength will increase, if the wavelength becomes longer than the

mean free path In physics, mean free path is the average distance over which a moving particle (such as an atom, a molecule, or a photon) travels before substantially changing its direction or energy (or, in a specific context, other properties), typically as a ...

in the medium (the average distance between scattering sites) then the scatterings can no longer be treated as independent events, this is the LPM effect. The Bethe–Heitler spectrum for multiple scattering induced radiation assumes that the scatterings are independent, the quantum interference between successive scatterings caused by the LPM effect leads to suppression of the radiation spectrum relative to that predicted by Bethe–Heitler. The suppression occurs in different parts of the emission spectrum, for

quantum electrodynamics In particle physics, quantum electrodynamics (QED) is the Theory of relativity, relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quant ...

(QED) small

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...

energies are suppressed, and for

quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the study of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of ...

(QCD) large

gluon A gluon ( ) is a type of Massless particle, massless elementary particle that mediates the strong interaction between quarks, acting as the exchange particle for the interaction. Gluons are massless vector bosons, thereby having a Spin (physi ...

energies are suppressed. In QED the rescattering of the high energy electron dominates the process, in QCD the emitted gluons carry color charge and interact with the medium also. Since the gluons are soft their rescattering will provide the dominant modification to the spectrum.

and Isaak Pomeranchuk showed that the formulas for bremsstrahlung and pair creation in matter which had been formulated by Hans Bethe and

Walter Heitler Walter Heinrich Heitler (; 2 January 1904 – 15 November 1981) was a German physicist who made contributions to quantum electrodynamics and quantum field theory. He brought chemistry under quantum mechanics through his theory of valence bondi ...

(the Bethe–Heitler formula) were inapplicable at high energy or high matter density. The effect of multiple Coulomb scattering by neighboring atoms reduces the cross sections for pair production and bremsstrahlung. Arkady Migdal developed a formula applicable at high energies or high matter densities which accounted for these effects. In 1994 a team of physicists at

SLAC National Accelerator Laboratory SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a Federally funded research and development centers, federally funded research and development center in Menlo Park, California, Menlo Park, Ca ...

experimentally confirmed the Landau–Pomeranchuk–Migdal effect.

References

Bibliography

* * {{particle-stub Scattering theory Lev Landau