Pomeron
Encyclopedia
In physics
, the pomeron is a Regge trajectory, a family of particles with increasing spin, postulated in 1961 to explain the slowly rising cross section of hadronic collisions at high energies.
of strong interaction
phenomenology. In later years, a BFKL pomeron was derived in other kinematic regimes from perturbative calculations in QCD
, but its relationship to the pomeron seen in soft high energy scattering is still incompletely understood.
One consequence of the pomeron hypothesis is that the cross sections of proton–proton and proton–antiproton scattering should be equal at high enough energies. This was demonstrated by the Ukrainian Soviet physicist Isaak Pomeranchuk
by analytic continuation assuming only that the cross sections do not fall. The pomeron itself was introduced by Vladimir Gribov
, and it incorporated this theorem into Regge theory
. Geoffrey Chew
and Steven Frautschi
introduced the pomeron in the west. The modern interpretation of Pomeranchuk's theorem is that the pomeron has no conserved charges—the particles on this trajectory have the quantum number
s of the vacuum.
The pomeron was well accepted in the 1960s despite the fact that the measured cross sections of proton–proton and proton–antiproton scattering at the energies then available were unequal. By the 1990s, the existence of the pomeron as well as some of its properties were experimentally well established, notably at Fermilab
and DESY
.
The pomeron carries no charges. The absence of electric charge implies that pomeron exchange does not lead to the usual shower of Cherenkov radiation
, while the absence of color charge
implies that such events do not radiate pion
s.
This is in accord with experimental observation. In high energy proton–antiproton collisions in which it is believed that pomerons have been exchanged, a rapidity gap is often observed. This is a large angular region in which no outgoing particles are detected.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, the pomeron is a Regge trajectory, a family of particles with increasing spin, postulated in 1961 to explain the slowly rising cross section of hadronic collisions at high energies.
Overview
While other trajectories lead to falling cross sections, the pomeron can lead to logarithmically rising cross sections which experimentally are approximately constant ones. The identification of the pomeron and the prediction of its properties was a major success of the Regge theoryRegge theory
In quantum physics, Regge theory is the study of the analytic properties of scattering as a function of angular momentum, where the angular momentum is not restricted to be an integer but is allowed to take any complex value...
of strong interaction
Strong interaction
In particle physics, the strong interaction is one of the four fundamental interactions of nature, the others being electromagnetism, the weak interaction and gravitation. As with the other fundamental interactions, it is a non-contact force...
phenomenology. In later years, a BFKL pomeron was derived in other kinematic regimes from perturbative calculations in QCD
Quantum chromodynamics
In theoretical physics, quantum chromodynamics is a theory of the strong interaction , a fundamental force describing the interactions of the quarks and gluons making up hadrons . It is the study of the SU Yang–Mills theory of color-charged fermions...
, but its relationship to the pomeron seen in soft high energy scattering is still incompletely understood.
One consequence of the pomeron hypothesis is that the cross sections of proton–proton and proton–antiproton scattering should be equal at high enough energies. This was demonstrated by the Ukrainian Soviet physicist Isaak Pomeranchuk
Isaak Pomeranchuk
Isaak Yakovlevich Pomeranchuk was a Soviet physicist, who was the founder and first head of the theory division at ITEP. The particle pomeron is named in his honour. For his work, Pomeranchuk was twice awarded Stalin Prize .-External links:**...
by analytic continuation assuming only that the cross sections do not fall. The pomeron itself was introduced by Vladimir Gribov
Vladimir Gribov
Vladimir Naumovich Gribov was a prominent Russian theoretical physicist, who worked on high-energy physics, quantum field theory and the Regge theory of the strong interactions.His best known contributions are the pomeron, the DGLAP equations, and the Gribov copies.-Life:Gribov completed his...
, and it incorporated this theorem into Regge theory
Regge theory
In quantum physics, Regge theory is the study of the analytic properties of scattering as a function of angular momentum, where the angular momentum is not restricted to be an integer but is allowed to take any complex value...
. Geoffrey Chew
Geoffrey Chew
Geoffrey F. Chew is an American theoretical physicist.He has worked as a professor of physics at the UC Berkeley since 1957 and has been an emeritus since 1991. Chew holds a PhD in theoretical particle physics from the University of Chicago. Between 1950 and 1956, he was a physics faculty member...
and Steven Frautschi
Steven Frautschi
Steven Frautschi is an American theoretical physicist, Professor of Physics at the California Institute of Technology. He is known for his contributions to the bootstrap theory of the strong interactions....
introduced the pomeron in the west. The modern interpretation of Pomeranchuk's theorem is that the pomeron has no conserved charges—the particles on this trajectory have the quantum number
Quantum number
Quantum numbers describe values of conserved quantities in the dynamics of the quantum system. Perhaps the most peculiar aspect of quantum mechanics is the quantization of observable quantities. This is distinguished from classical mechanics where the values can range continuously...
s of the vacuum.
The pomeron was well accepted in the 1960s despite the fact that the measured cross sections of proton–proton and proton–antiproton scattering at the energies then available were unequal. By the 1990s, the existence of the pomeron as well as some of its properties were experimentally well established, notably at Fermilab
Fermilab
Fermi National Accelerator Laboratory , located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics...
and DESY
DESY
The DESY is the biggest German research center for particle physics, with sites in Hamburg and Zeuthen....
.
The pomeron carries no charges. The absence of electric charge implies that pomeron exchange does not lead to the usual shower of Cherenkov radiation
Cherenkov radiation
Cherenkov radiation is electromagnetic radiation emitted when a charged particle passes through a dielectric medium at a speed greater than the phase velocity of light in that medium...
, while the absence of color charge
Color charge
In particle physics, color charge is a property of quarks and gluons that is related to the particles' strong interactions in the theory of quantum chromodynamics . Color charge has analogies with the notion of electric charge of particles, but because of the mathematical complications of QCD,...
implies that such events do not radiate pion
Pion
In particle physics, a pion is any of three subatomic particles: , , and . Pions are the lightest mesons and they play an important role in explaining the low-energy properties of the strong nuclear force....
s.
This is in accord with experimental observation. In high energy proton–antiproton collisions in which it is believed that pomerons have been exchanged, a rapidity gap is often observed. This is a large angular region in which no outgoing particles are detected.