September 2, 1997
Physicists Find Exotic New Particle
By MALCOLM W. BROWNE
hysicists working at Brookhaven National Laboratory on Long Island believe
they have discovered a previously unknown particle, which they call an
exotic meson.
The discovery of the new particle was reported Monday in the journal
Physical Review Letters by 51 scientists from Brookhaven, the University of
Notre Dame, three other American institutions and two Russian research
groups.
The particle, which was created by hurling a beam of protons into a target
of liquid hydrogen, has too short a life to be detected directly, but
physicists deduced its existence from the pattern of subnuclear debris its
decay apparently created.
Ordinary matter consists of atoms whose nuclei are made of varying
combinations of protons and neutrons, and each proton or neutron contains
three quarks, with particles called gluons holding them together. Another
type of particle, which survives briefly after creation in accelerator
laboratories, is the meson: a particle containing just two quarks -- a
quark and an antiquark.
The suspected new meson is definitely not one of the well known
quark-antiquark kinds, the group reported. Among the possibilities the
collaboration intends to investigate is that the new particle might contain
four quarks -- two normal ones and two antiquarks -- bound together by
gluons. This would make the exotic meson the only known particle containing
more than three quarks.
The scientists said that although the existence of this particle was not
predicted by the generally accepted theory of matter known as the Standard
Model, the particle was not inconsistent with that theory.
Further study of the peculiar new particle is expected to shed light on
details of the strong nuclear force and the theory of quantum
chromodynamics -- a key to understanding the structure of matter.
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