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.
It is named after Isaak Pomeranchuk.
== 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 theory of strong interaction
phenomenology.
In later years, a BFKL pomeron was derived
in further kinematic regimes from perturbative
calculations in QCD, but its relationship
to the pomeron seen in soft high energy scattering
is still not fully 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 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 numbers 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.
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 pions.
This is in accord with experimental observation.
In high energy proton–proton and 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.
== Odderon ==
The odderon, the counterpart of the pomeron
that carries odd charge parity was introduced
in 1973 by Leszek Łukaszuk and Basarab Nicolescu.
It was potentially observed only in 2017 by
the TOTEM experiment at the LHC.
Odderon exists in QCD as compound state of
3 reggeized gluons.
== String theory ==
In early particle physics, the 'pomeron sector'
was what is now called the 'closed string
sector' while what was called the 'reggeon
sector' is now the 'open string theory'.
== See also ==
Giuseppe Cocconi
