Andre Rubbia: The LAGUNA Project
The Laguna consortium has 100 members from 10 states. We all agree there has to be a multi-purpose neutrino observatory, for SN, the sun, from the earth, and for the rest of neutrino studies. The LBNO approach to CP violation and mass hierarchy can be described by exploring and resolve these issue by observing clear signatures and ascertaining their L/E dependence. This approach is different from extracting MH or CPV from multidimensional fits that combine several experimental measurements, since global fits cannot replace a direct evidence, and we are seeking direct signal patterns.
A fully conclusive knowledge of matter effects and of neutrino Mass hierarchy is a mandatory prerequisite to any CP violation search. There is a zoom effect: the L/E dependence can be observed in an expanded scale at large L, so we measure the full spectral information for unambiguous sensitivity and a direct proof of the observed phenomenon. At medium and short baselines the absence of knowledge of MH can compromise the efforts to discover CPV.
The CP violation measurement is one of sub-leading oscillation effects, so compared to present generation discovery experiments, the next generation will require precision, so a more than ten-fold increase in statistics and an improved knowledge of systematics. The right detector mass is above 20 kton, but of course we do not know if the CP effect may be large or small. That is why we advocate an incremental approach, with an initial LAr mass of 20 kton, to be complemented by a 50 kton mass in a second phase, each with significant physics reach and chances to find CPV. One must of course have a design that provides scalability and cost-effectiveness.
The far site proposed is the Pyhasalmi mine. An extended site investigation is in progress, to understand the quality of the rock. Only those parts that are necessary for LAGUNA during construction and operation would be transferred to the new entity. The mine is at 1400 m depth. A possible configuration would see a 20kton detector in one cavern, a 50kton module in a second, and there would be the possibility to complement the two with a scintillation detector. The detector requirements are several: a fiducial mass must be at least equal to that of Super-K, clean neutrino detection in the neergy range 0.5 – 10 GeV, low backgrounds. A design of the LAr detector tank is ready. In their report they detail (475 pages) the various ideas, the scalability, the engineering designs. More reports are in preparation.
There are three versions, at 20,50, and 100 kton sizes. All vessels have 20m height. They are considering building a large scale demonstrator, to operate as a prototype.
Rubbia presented a sensitivity plot to CP violation phase with a 20 and 70 kton scenario. This appears similar to the one shown in the Hyper-K talk which preceded this one.
In summary, LAGUNA is a project with a very rich and interesting physics program with fundamental discovery potential. Much progress has already been achieved in defining a very long baseline experiment in Europe. Challenging, but initial studies show that it offers unique and attractive possibilities. R&D efforts are shifting focus to large scale demonstrators. They need more collaborators and more support from the community. The project is open and still being defined.