First neutrino from CERN detected in OPERA Print E-mail
On the 2nd October, one of the many billions of neutrinos produced at CERN left for the first time its trace in the OPERA detector at the Gran Sasso Laboratory, after a 730 km trip underground at nearly the speed of light.
On the 2nd October for the first time, one of the many billions of neutrinos produced at CERN left its trace in the OPERA detector at the Gran Sasso Laboratory of the Italian Institute for Nuclear Physics (INFN). A 730 km trip underground at nearly the speed of light is what a neutrino of the CNGS project (CERN Neutrinos to Gran Sasso) covers in about 2.4 milliseconds. The main goal of the experiment is to shed light on the mysterious phenomenon of the oscillations of neutrino oscillation.

Opera track

The display of an event, where a neutrino interacted inside one brick, analyzed by the microscopes. The neutrino, coming from the left of the figure, after an interaction, produces several particles identified by their tracks in the brick. Credits: © INFN
Neutrinos are the second most abundant particles in the Universe, after photons. They are produced in nuclear reactions like the ones occurring within stars, and their intense flux continuously traverses our planet and ourelves: each square centimetre of our body is traversed by 60 billion neutrinos each second. To be studied, neutrinos can be artificially produced by exploiting the high-energy collisions between particle beams and targets.

Neutrinos are very peculiar particles. Unlike charged particles, they don’t interact with matter through the electromagnetic force, and not even through the strong force that holds together the nucleus of an atom. Neutrinos can only be affected by other particles through the weak force (involved, for example, in the nuclear fusion in the stars), which has a very little probability to play. Neutrinos can therefore pass through almost any kind and thickness of matter without leaving any traces, while maintaining the same direction of motion they had from their “birth”. The neutrinos of the CNGS beam, created from the particle beams at CERN, travel without deviations along a straight path through the Earth’s crust.

All neutrinos belong to one of three possible families: electronic, muonic or tauonic, on the base of a characteristic that physicists call “flavour”. Experimental evidence confirms the original idea proposed by Bruno Pontecorvo that a neutrino can oscillate from one type into another when travelling long distances. Due to this “flavour oscillation”, a neutrino beam of one type detected after a relatively long distance from its creation could contain neutrinos of a different type. Since the beam from CERN contains only muon-type neutrinos, the observation of a few tau neutrinos in the OPERA detector would be the proof of the direct conversion of one type of neutrino into another.

The flavour oscillation would also demonstrate that neutrinos have mass. From the theory, the probability of this phenomenon depends, among other things, on the mass difference between the original and the final neutrino. Thus if neutrinos oscillate from one type to another, their mass that cannot be zero. As neutrinos are the second most abundant particles in the Universe, wether or not they have a mass has a great influence on our idea of the Universe. This could explain, for example, some types of symmetry-breaking, as the fact that matter overcame antimatter.

OPERA is an enormous detector weighing 1.800 tons, which is now progressively being completed. Its “heart” is made of more than 150000 small units called “bricks”, each equivalent to a sophisticated photographic camera. The neutrino event of 2nd October hit one of the almost 60000 bricks already installed and it has been followed by about 10 more events in the following days.

OPERA has been designed and realized by a large team of researchers from all over the world (including those from Belgium, Croatia, France, Germany, Israel, Italy, Japan, Korea, Russia, Switzerland and Turkey) with the specific goal of identifying the elusive tau neutrino from the oscillation process.

The successful start-up of OPERA is one more confirmation that a truly international scientific cooperation is a required ingredient to successfully meet the challenge of modern research in fundamental and applied science.

Submitted by Francesca Scianitti (INFN)


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>> CNGS website



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