name is Y(4260) and it is not a new humanoid of Stars
Wars, but a particle identified for the first time
by BaBar experiment: an international collaboration
- formed by the large participation of the Italian
physicists of the National Institute for Nuclear
Physics (Infn) - that has its seat in Stanford (California).
Y(4260) represents an interesting element with
respect of particles' field and it will provide
very useful signs about character of the strong
force, that is the force that holds together the
different particles inside atomic nuclei. The discovery,
announced during the international symposium “Lepton
Photon” just finished in Uppsala in Sweden, has been presented today during a
meeting of the Supervising Committee of Babar experiment that this year has taken
place in Rome, by the seat of Infn Headquarter.
“At first sight Y(4260) seems to be what we call a charmonic state, that is to
say a particle made up of the combination of a charm quark and of its equivalent
antiparticle: an anticharm quark”, explains Marcello Giorgi, Infn researcher,
professor of Physics at Pisa University and involved in Babar experiment since
a long time.
Physicists have known since some time that for each particle, an antiparticle
exists, nearly identical in all aspects, except for some properties that are
opposite. The antiparticle of the electron is for instance the positron, named
also antielectron, provided with positive electric charge, rather than negative.
During the 50's it was although discovered that particles can be made up also
of the combination of a fundamental particle and its corresponding antiparticle. “The
first case was the positronium one, made up of the combination of an electron
and a positron. The first charmonium, that is to say a particle made up of a
charm quark and anti-charm, was instead discovered at the same time in Brookhaven
and at Slac, both in the USA, by Samuel Ting and Burton Richter, awarded with
the Nobel in 1976: its existence it was soon afterwards confirmed thanks to the
analysis of the data produced in Italy by the National Laboratories of Frascati
of Infn. As time passed, it was realized that charmoni are a real family of similar
particles, but with a different mass. Nobody had been able to observe Y(4260)
up to now, not only because there is a little possibility to produce it in the
accelerators used today by physicists, but also because it is extremely unstable”,
explains Mauro Morandin, Infn researcher and national spokesman of BaBar experiment.
“Compound particles, made up of the combination of a fundamental particle and
its corresponding antiparticle, are of great interest for physics. Quarks and
corresponding anti-quarks can be held together because of several mechanisms:
in order to understand the so-called strong force [the strong force is one of
the four fundamental forces of nature, the other are the electromagnetic force,
the weak force, responsible for fusion mechanisms occurring inside stars and
the gravitational force] it is necessary to grasp these mechanisms deeply. The
strong force holds together quarks of different type that form neutrons and protons,
and holds also neutrons and protons together inside atomic nuclei. It is therefore
a very important force, because without it would be impossible to conceive the
existence of matter that forms all we know. All signs let us suppose that Y(4260)
will give very interesting indications about it, whether it is really a charmonium,
or, all the more so, something more exotic”, concludes Marcello Giorgi.
The most surprising aspect of Y(4260) is although the fact that some properties
of its nature seem to be unusual for a charmonium. This makes think that the
particle could be something much more complex: a kind of molecule made up of
particles named D mesons, or a state made up of four quarks. Since 2003 BaBar
has discovered states that can have this structure never observed before, such
as the DsJ (2317), the DsJ (2458), and the X(3872), but there are no definitive
evidences for this interpretation.
Verifying these possibilities is the challenge for the next future.
For further information, please contact:
Istituto Nazionale di Fisica Nucleare (INFN)
+39 39050 2214281, 39 348