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  24-07-2002: BABAR ANNOUNCES NEW RESULTS ON CP VIOLATION 
 COMPLETE LIST 
The preparation of the BaBar experiment
The preparation of the BaBar experiment



BaBar in construction
BaBar in construction


From theory to certainty

A new important result reached by the BaBar International Cooperation will be announced on Thursday, July 25th, within the international conference on high energy physics which is now taking place in Amsterdam. The BaBar International Cooperation is active at the matter-antimatter collider at the Stanford, California, University and it includes a great number of researchers from the Italian National Institute for Nuclear Physics (Infn). The present result concerns the improvement of the measurement of the parameter known as sinus 2 beta, a measure of the degree of asymmetry between matter and antimatter. This data offers an accurate experimental confirmation of the theoretical expectation and it will become part of a solid basis of knowledge from which to start from to progress in the discovery of our Universe.

Something is missing in the comprehension of how the Universe we live in has evolved to reach the form it has now. Theoretical studies suggest that an equal quantity of matter and antimatter, which is identical to matter except for its opposite charge, formed when the Big Bang occured. Almost immediately, matter and antimatter started to collide annihilating each other to generate pure energy. From this process a bit of matter was mysteriously ‘left over’. This small quantity was nonetheless sufficient to build the stars, the planets, ourselves and everything we know in the Cosmos. Therefore, all we see and even our own existence must be traced back to a primordial asymmetry between the quantity of matter and antimatter, in favour of the first. But just how and when did this phenomenon, technically called CP violation, come about? This question represents one of the most fascinating research themes that engage modern high energy physics.

The objective of the BaBar experiment, currently collecting data at Stanford, is to study the particles known as B mesons as well as their antimatter counterparts, the anti-B mesons. It’s an extremely difficult task, since these particles have a very short lifetime, only a billionth of a second. B and anti-B mesons are identical except for their charge, which is of opposite signs. Therefore, any difference in their behaviours is an indication that there is a difference between matter and antimatter and it confirms the existence of a CP violation. One of BaBar’s first results, announced in the summer of 2001, had already given a clear signal that there was an asymmetry between the two particles. The new data, however, is even more accurate than the first and it is perfectly in line with expectations of the Standard Model, the theory that physicists consider the best explanation of the behaviour of particles today.

We owe the result announced in Amsterdam to the study of about 100 million couples of mesons and anti-mesons, produced through the collision of electron beams and their antimatter counterparts, positrons. Mesons decay almost immediately after they are generated, forming other particles whose peculiarities are measured by a detector that also reveals the precise point they were produced from. By analysing this data it was possible to observe the extremely subtle difference between the B meson and the anti-B meson’s behaviours.

The BaBar cooperation comprises physicists from various countries. The Italian component, co-ordinated by Fernando Ferroni from “La Sapienza” University and the Rome Infn section and by Mauro Morandin from the Padoa University and Infn section, is second in number only to the American component. The Italian groups working on the BaBar experiment do so from their Infn sections and laboratories and from university departments situated in Bari, Ferrara, Genoa, Milan, Naples, Padoa, Pavia, Pisa, Rome, Turin and Trieste. They have contributed significantly to Slac’s experiment. The construction of the high resolution silicon tracking detector (which is the Infn’s true field of excellence) is particularly significant. Other important projects were the design of electronic chips for signal read-out and rapid elaboration, the contribution to the construction of a gaseous detector (using sophisticated robotic techniques designed in Italy) and the construction of a great number of special tracking detectors also developed in Italy. Lately, Infn also built a calculus centre for the analysis of the massive quantity of data produced by BaBar at the Physics Department of the University of Padoa. Various Italian industries played an important role in all the aforementioned highly technological applications.
It bears separate mention that Infn contributed the superconducting magnet central to the experiment, built by the Ansaldo firm in Genoa in close collaboration with Infn.


 RELATED SITES 
http://www.slac.stanford.edu/BFROOT/
http://www.slac.stanford.edu/BFROOT/

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