| Topic: |
Science > Physics |
| User: |
"Dr. Jai Maharaj" |
| Date: |
15 Nov 2003 11:18:47 PM |
| Object: |
NEW PARTICLE TURNS UP IN JAPAN |
New particle turns up in Japan
PhysicsWeb
Friday, November 14, 2003
The Belle collaboration at the KEK laboratory in Japan
has discovered a new sub-atomic particle which it is
calling the "X(3872)". The particle does not fit into any
known particle scheme and theorists are speculating that
it might be a hitherto unseen type of meson that contains
four quarks (arxiv.org/abs/hep-ex/0309032; Phys. Rev.
Lett. to be published). The discovery has been confirmed
by the CDF collaboration at Fermilab in the US, where the
new particle is being called the "mystery meson".
Mesons are particles that contain a quark and an
antiquark that are held together by the strong nuclear
force. Since there are six different "flavours" of quark
- up, down, strange, charm, bottom and top - it is
possible to form a large number of different mesons.
The Belle team measured the decay of B-mesons - mesons
that contain a bottom quark - produced in electron-
positron collisions at the KEK B-factory in Japan. The
team plotted the number of candidate events for B mesons
against mass and observed a significant spike in the
distribution at 0.775 GeV. This corresponds to a mass of
nearly 3872 MeV. The particle decayed almost immediately
into other, longer lived particles.
The KEK team says that the mass of this new meson is
higher than theoretical predictions. Moreover, the way in
which it decays also differs from theory. One possibility
is that current models of the strong force need to be
modified. Alternatively it could be that X(3872) is the
first example of a "molecular state" meson that contains
two quarks and two antiquarks.
Until recently particle physicists had only ever detected
particles that contain two or three quarks. However, in
the past year evidence has emerged for another four-quark
particle known as the Ds(2317) and a five-quark particle
known as the pentaquark.
Author
Belle Dumé is Science Writer at PhysicsWeb
Read the complete news at:
http://physicsweb.org/article/news/7/11/7
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