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  29-04-2003: A NEW INTERESTING PARTICLE FOUND BY INFN RESEARCHERS 
 COMPLETE LIST 

© Copyright 2002 INFN The use of photos is free of charge. Please request authorisation from the INFN Communication Office


© Copyright 2002 INFN The use of photos is free of charge. Please request authorisation from the INFN Communication Office

The announcement has been made on 28th of April in Stanford

It is thanks to a group of Italian researchers if a new, absolutely unexpected particle was discovered. The particle named Ds (2317) is part of the meson family and its mass is about two and a half times the proton's. The announcement has been made in Stanford on Monday 28th of April at the Stanford Slac Laboratory in the US, during a seminar held by Antimo Palano a Physicist of the Infn and of the University of Bari who has analysed the data. The existence of this particle has been observed through the use of computers of the University of Rome, within the BaBar experiment, an international collaboration where the National Institute of Nuclear Physics (Infn) participates for Italy.

The first tests indicate that the particle consists of a charm quark and a strange antiquark. Six types of quarks exist in nature, but neutrons and protons, which form the nuclei of those atoms that form matter, are made only by 2 quarks called Up and Down, the lightest. The heaviest quarks existed only in the first instants of life of the Universe, while today they are created very seldom by collisions between cosmic rays and the atmosphere or by particle accelerators. The existence of the particle is not surprising by itself, what surprises the researchers is its mass, which is lower than predicted by theoretical calculations. "There are two possibilities" explains Mauro Morandin, who coordinates the group of Italian physicists involved in the experiment: "either the model does not reproduce reality, and it is therefore necessary to rethink it in a significant way, or this new particle is made by a combination of quarks that has never been observed before. There's no doubt that physicists will be very excited about this more exotic hypothesis." In particular, this new meson seems to have unexpected properties that could help to understand the nature of the forces that hold quark together (for example, inside protons and neutrons). They are somewhat particular forces, in fact their entity grows as the distance between quarks increases, contrary to what happens with the elctromagnetical and gravitational forces.

Marcello Giorgi, Infn researcher and spokesman of the international collaboration that has made the finding says: "This result is very important for BaBar. We have found this new particle during an experiment that had been thought to study the asymmetry between matter and antimatter analysing Bottom quark behaviour: this is an example of how sometimes, the most exciting discoveries happen unexpectedly. We have carefully analysed experimental data produced since 1999. These data evidence that 1500 such mesons have been observed."

The BaBar experiment is based in the Stanford Linear Accelerator Centre (Slac), in California (Usa), using the Pep-II accelerator. About 600 physicists from 10 different nations participate in the experiment. The construction of the apparatus began in 1994, and researchers began collecting data in 1999. The first important result was reported in 2001. It consisted in the confirmation with high precision of the asymmetry between matter antimatter in the case of the Beauty quark. Italy participates in this experiment with 10 universities and Infn sections, totalling about 90 physicists. The Italian group occupies a very relevant position within BaBar. So much so, in fact, that the two most important roles in the collaboration are now covered by Infn researchers: Marcello Giorgi, professor at the University of Pisa and spokesman for the BaBar experiment, and Livio Lancieri, professor at the University of Trieste and coordinator of the analysis activities. Italy also constructed or participated in the construction of fundamental parts of the experimental apparatus, such as the muon detector, the drift chamber or the superconducting magnet.


 RELATED SITES 
http://www-public.slac.stanford.edu/babar/
http://hepweb.rl.ac.uk/ppUKpics/index/slac-2.htm

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