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  31-05-2010: THE METAMORPHOSIS OF A NEUTRINO DIRECTLY OBSERVED FOR THE FIRST TIME 
 COMPLETE LIST 
Lucia Votano, LNGS director. In the background the Opera Experiment
Lucia Votano, LNGS director. In the background the Opera Experiment

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


The Opera
The Opera "bricks"

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



After more than three years of research and the passage of billion of billions of particles travelling from one part of the Alps to another, the metamorphosis of a neutrino has been directly observed for the first time ever, at the Gran Sasso National Laboratories of the Italian National Institute for Nuclear Physics (Istituto Nazionale di Fisica Nucleare - INFN) in Gran Sasso (LNGS). This metamorphosis consists of the transformation of one type of neutrino into another, a result that will pave the way for New Physics, although it will obviously have to be confirmed by additional observations of "mutating" neutrinos such as this first one.
The phenomenon was observed by the international collaboration OPERA (Oscillation Project with Emulsion-tRacking Apparatus). Neutrinos are "shot" from the European laboratory of CERN in beams directed to the Gran Sasso: in a mere 2.4 milliseconds they travel 732 kilometres beneath the Earth's crust to the core of the Gran Sasso Mountain in the Abruzzo Region and, during their journey, there is the possibility that some of them “change” their nature. The observation of this “mutation” was made possible by a fruitful collaboration between the OPERA researchers, CERN and the INFN Laboratories in Gran Sasso, within the CNGS neutrino beam project.
A single candidate neutrino that turned (in particle physics is called “oscillation”) from a muon neutrino into a tau neutrino was detected by the OPERA scientists, who since 2007 have observed several thousands of “normal” muon neutrinos sent by CERN and received at LNGS. This observation is a strong evidence that neutrinos have mass and that they can oscillate, passing from one “family” to another. That neutrinos can transform themselves was first proposed around the mid-20th century by the Italian physicist Bruno Pontecorvo, who was part of Enrico Fermi's group of researchers “Via Panisperna Boys”. In the Standard Model developed by physicists to explain the Universe, neutrinos do not have mass; it will thus be necessary to rectify this model, to provide new explanations, and to begin new research, which could have diverse implications in Cosmology, Astrophysics, and Particle Physics.
For 15 years a number of experiments have revealed the neutrino oscillation through disappearance of neutrinos coming from the atmosphere, the Sun, and other sources. However, this is the likely the first time that a neutrino that has oscillated from one type into another has been directly observed. It is as if, after having learned of a crime, the victim's body has finally been found.
OPERA is an experiment designed and realized by a rather large group of researchers from universities and scientific institutes in Belgium, Croatia, France, Germany, Israel, Italy, Japan, Korea, Russia, Tunisia, Switzerland, and Turkey. The Italian researchers involved in OPERA are represented by the University and INFN section of Bari, the University and INFN section of Bologna, the National INFN Laboratories of Frascati, the National INFN Laboratories of Gran Sasso, the University of L’Aquila, the "Federico II" University and INFN section of Naples, the University and INFN section of Padova, the "La Sapienza" University and INFN section of Rome, and the University of Salerno.

To download infographics, videos, animations, and images, go to:
www.infn.it/comunicazione/materiale
password stampa
cartella Neutrino Tau


Quotes
Antonio Ereditato, Spokesperson of the OPERA collaboration, “An important result which rewards the entire OPERA collaboration for its years of commitment and which confirms that we have made sound experimental choices. We are confident that this first event will be followed by others that will fully demonstrate the "appearance" of neutrino oscillation".

Lucia Votano, Director of the INFN Laboratories of Gran Sasso, “The OPERA experiment has reached its first goal: the detection of a tau neutrino obtained from the transformation of a muon neutrino, which occurred during the journey from Geneva to the Gran Sasso Laboratory. This important result comes after a decade of intense work performed by the Collaboration, with the support of the Laboratory, and it again confirms that LNGS is a leading laboratory in Astroparticle Physics”.

Roberto Petronzio, President of the INFN, “This success is due to the tenacity and inventiveness of the physicists of the international community, who designed a particle beam especially for this experiment. In this way, the original design of Gran Sasso has been crowned with success. In fact, when constructed, the laboratories were oriented so that they could receive particle beams from CERN”.

Eugenio Coccia, former Director of the INFN Laboratories of Gran Sasso, ''Having managed the LNGS over the whole realization of the Opera experiment and during the first years of the neutrino beam, in a difficult period for the territory of Gran Sasso, I can attest that this success is the result of a team work. It involved the passion of the members of the experiment, the perseverance of the LNGS staff and the far-sightedness of INFN management."


For interviews

Romeo Bassoli, Head, INFN Press Office
Tel +39 066868162 – cell +39 3286666766
romeo.bassoli@presid.infn.it

Roberta Antolini, Relazioni Esterne, Gran Sasso Laboratories
Tel +39 0862437216
antolini@lngs.infn.it

Antonio Ereditato, OPERA Spokesperson,
University of Bern
Tel +41 31 6318566
Cell +41 793690906
Cell +39 347 3394916
antonio.ereditato@cern.ch

Lucia Votano, Director, INFN Gran Sasso Laboratories
Tel + 39 06 94038175 - Tel +39 0862437 230
lucia.votano@lngs.infn.it

Learn more
The OPERA Experiment


The OPERA experiment consists of a detector which contains as a neutrino target 150,000 “bricks” made of a sandwich of lead plates and photographic emulsion films. This target weighs 1,250 tons and is a sort of extremely sophisticated photographic camera. Using this detector, complemented by other complex electronics devices, researchers can observe the consequences of the interaction of neutrinos with the target and infer information on their nature. The neutrinos originate from CERN in Geneva, where they are created through a series of passages through the CERN accelerator complex. The particles travel in a straight line through the earth at nearly the speed of light, until reaching Gran Sasso. In fact, neutrinos can pass through extremely thick layers of matter without interacting at all, and only a small fraction of them actually interacts with the OPERA apparatus. For this reason, despite that fact that thousand of billions of neutrinos are sent from CERN each day, only about 20 of them interact in the target at LNGS, whereas the other neutrinos continue their journey, emerging to the surface and hurling themselves into space.
 The OPERA collaboration presently involves 170 researchers from 33 institutions in 12 countries.



The oscillation of neutrinos


OPERA has observed, for the first time ever, the phenomenon of the appearance of a neutrino of a different "family" with respect to the original one when it left CERN. This process was first hypothesized by the Italian physicist Bruno Pontecorvo, in the mid-20th century. The premise is that neutrinos do not possess a defined mass but that they consist of a combination of states, each with an own different mass. It is as if there were two components (i.e., a muon component and a tau component). Neutrinos with different masses evolve differently, and the OPERA experiment “plays upon” exactly this concept. Only muon neutrinos are sent from CERN. After they have completed a certain portion of their trajectory, the two components that make up the neutrino undergo a sort of mixing. In this way, the original neutrino takes on an increasingly larger tau component: in other words, it begins to oscillate. After a certain interval of time, or after having completed a certain journey, a large fraction of the muon neutrinos is transformed into tau neutrinos. The oscillation then continues in the same way, with a decrease in the tau component, and neutrinos are again transformed back into muon neutrinos.



The New Physics


The Standard Model of particles and interactions, in particular its predictions regarding neutrinos, is certainly put in question by neutrino oscillations and by the first results from OPERA. Until now, this Model had been strongly confirmed by the discoveries of the LEP accelerator at CERN (i.e., the accelerator that was developed in the 1990s and preceded the LHC), by Tevatron of the Fermilab in Chicago and by the early results of the LHC. Now the way has been paved for New Physics which will lead to extensions or revisions of Standard Model. One thing is certain: based on the existence of New Physics, the fundamental components of the Standard Model will have to be expanded to make room for the possibility that there exist new mechanisms (or new particles) which guarantees the mass of neutrinos, as forced by the existence of neutrino oscillations. One fascinating possibility is that this new particle is a new type of neutrino never seen before. It could be a neutrino with an extremely large mass, that is, millions of billions of Giga electron Volts (GeV). Another possibility currently being investigated by physicists is that a much lighter form of a neutrino could constitute part of the famous Dark Matter that, together with the so-called Dark Energy, dominates the total mass of the Universe.


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