Neutrinos from CERN to Gran Sasso

Europhysics News, Jul 2018

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Neutrinos from CERN to Gran Sasso

Neutrinos from (ERN to GranSasso Gran Sasso - round 2005 CERN will start aiming A pulses of neutrinos at INFN's Gran Sasso National Laboratory, the world's largest underground laboratory deep un­ der a mountain about an hour driving East from Rome. During the 730 km trip, some neutrinos will change flavour, and two detectors at Gran Sasso will try to de­ tect these changed neutrinos. At that time similar experiments will be well under way in the United States and Japan. Japan start­ ed sending neutrinos from the KEK pro(ERN's accelerator complex LEP -LHC ton synchrotron in Tsukuba over a dis­ tance of 250 km to the SuperKamiokande underground detector, and the Fermi Na­ tional Laboratory (Fermilab) near Chica­ go is gearing up to aim neutrinos at a de­ ~ctor in the Soudan Underground Labo­ ratory in Minnesota, also 730 km away, in 2003. However, unlike these two experi­ ments that try to detect a deficit of a cer­ tain flavour of neutrino-a "disappearance experiment", the CERN-Gran Sasso ex­ periments will try to detect different neu(ERN Neutrinos to Gran Sasso facility I I Germany France .I\.~rlan" CERN-""~ Austria Italy • >;] • .r,(>'" ..,~,!! U "CNGS: Cern Neutrinos to Gran Sasso" a new facility to explore the physics beyond the Standard Theory trinos than those produced at CERN­ those that actually changed their flavour. The CERN Council approved the 60 mil­ liQn Euro experiment in December, and it will be financed by INFN for more than 50%. Neutrinos come in three flavours: elec­ tron neutrinos, muon neutrinos, and tau neutrinos. Several experiments suggest strongly that neutrinos may oscillate, that is, change from one flavour into another while travelling through space or matter. For example, less neutrinos are detected from the sun as predicted by theory--they probably escape the detectors by changing flavour. Also, the SuperKamiokande de­ tector in Japan detects different ratios be­ n.veen electron and muon neutrinos pro­ duced in the atmosphere by cosmic rays if they travel over longer distances through Earth. And if neutrinos oscillate, they must have mass, according to theorists. But some particle physicists still doubt whether neutrino oscillation is a reality. At CERN, a proton beam extracted from the SPS (Super Proton Synchrotron) will hit a graphite target, producing a vari­ ety of particles. Among them are pions that will be nudged by magnets into a beam pipe directed towards Gran Sasso. In the beam pipe they will decay into muons and muon neutrinos. The muons will be stopped while the neutrinos will travel on to Gran Sasso, whereby some of them will change into tau neutrinos. Two detectors, OPERA and ICANOE, will look for these tau neutrinos. Not only are the transformations from muon to tau neutri­ nos rare events, but because very few neu­ trinos interact with matter, scientists ex­ pect that only a few ofthem will be'detect­ ed during a period of at least five years, says Paolo Strolin at the University of Naples. Therefore the background--events that mimic neutrino events--has to be ex­ tremely low for the experiments to be meaningful, says Stolin. The experi­ menters expect one such event every two years. The great advantage of long-baseline experiments is that one controls the neu­ trino source and does not depend on un­ known factors influencing neutrino pro­ duction in the sun or by cosmic radiation, says Alessandro Bettini, Director of the Gran Sasso Laboratory. And Alessandro Pascolini of Padua University and INFN is confident that the long- baseline experi­ ments will help settle the matter of neutri­ no oscillations. Especially, the positive de­ tection of tau neutrinos at Gran Sasso will leave no doubt that neutrinos do oscillate and have mass, he says.


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Neutrinos from CERN to Gran Sasso, Europhysics News, 17-17, DOI: 10.1051/epn:2000305