Kenneth Long introduced the open discussion session. He chairs the ICFA neutrino panel. They just finalized a neutrino roadmap, so he went through it. The programme must have discovery potential and deliver critical measurements in the short and medium term. And develop the capabilities required to outperform the present and next-generation experiments.
Among its assignments, ICFA should encourage timely consideration of the development of the hadro-production measurement programme; it should encourage nad promote a sustained effort towards reliable and precise calculations of neutrino-nucleus scattering processes. It should complete the present detector R&D programme and make provision for an appropriately resourced detector deveopment programme over the lifetime of the next generation experiments. Other assignments include a census of accelerator-based neutrino community, and a new 4th international meeting on large neutrino infrastructures.
Yifang Wang briefly discussed the unknowns of neutrinos. There are a number of them: the parameters we try to measure – the oscillation parameters, the CP phase, etcetera; and in general the unitarity of the matrix. There is the neutrino mass, the issue of Dirac vs Majorana, the existence of steriles, their magnetic moments. For some of the above items, we do not have reason to believe we can find a solution in the short term. He considered the present experiments, in particular JUNO, and made the point that there needs to be a global coordination to construct huge detectors at the scale of billions of dollars to increase our understanding and detect neutrino masses, double beta decay, and magnetic moments, or other important questions that at the point remain unaccessible.
Antonio Masiero discussed the role of multi-messenger in the APPEC (astroparticle physics european coordination) roadmap. The next generation of astroparticle physics research infrastructures require substantial capital investment. So there needs to be a resource aware strategy. European astroparticle physics does not profit from a natural and strong intergovernmental organization like CERN, ESO and ESA to drive the field. In 2001 APPEC was found to coordinate the field. The “C” in APPEC since 2012 means “consortium”. This has a profound meaning. APPEC must formulate and realize the european astroparticle physics strategy.
In 2008 the roadmap included the “magnificent 7”, HE gammas, neutrinos, and cosmics; gravitational waves, dark matter, neutrino mass, and neutrino mixing and proton decay. However at least four or five of these domains have not seen a signal yet. However the situation has now changed, as two of them have seen new signals: astrophysical sources of neutrinos and gravitational waves.
The new map, coming out now, and there are now 9 topics of relevance. Dark energy and the CMB have entered the club of astroparticle items to be followed by the european agencies for astroparticle physics.
Masiero explained that with its global partners and in consultation with the gravitational wave international committee, APPEC will define timelines for upgrades of existing as well as next-generation ground-based interferometers. APPEC strongluy supports further actions strenghtening the collaboration between gravitational-wave laboratories. For neutrinos, APPEC strongly supports the present range of direct neutrino-mass measurements and searches for neutrinoless double-beta decay. Guided by the results of running experiments and in consultation with its glibal partners, APPEC intends to converge on a roadmap for the next generation of experiments into neutrino mass and nature by 2020.
Note of the editor: It is interesting that while the 2009 report had Ursa Major in the cover, the 2016 report has the Leo constellation. Is this a message in itself ? Masiero explained that it was driven by going from 7 to 9 hot topics, as the number of stars in the constellations.
Masato Shiozawa explained what is the program leading to Hyper-Kamiokande, envisioned to start in 2026. It involves gradual upgrades to both the detector and the accelerator facility. Hyper-Kamiokande will have a mass of 190 ktons, impinged by a 1.3MW beam. It is a seamless program to get timely results, with a rich physics program and big chances of discoveries. For proton decay, HK will be able to reconstruct the proton mass and have zero background, so that one event would be a discovery, and this can push lifetime limits above 10^35. It will have sufficient angular sensitivity to point to SN sources within 1 degree, to alert other telescopes, up to Mega-parsec distances.
Soo-Bong Kim took a broad view of the neutrino science. He made the point that we need to study more SN burst and extend our search to more distant supernovas, as the number of burst is too rare otherwise. In Hyper-Kamiokande the sensitivity will extend to Megaparsecs away.
In Korea they are interested in having one of the Hyper-Kamiokande detectors there. They can receive the J-PARC beam 1100 km away. There are several candidate sites. They can have 1000m overburden, to be sensitive to low-energy physics.
When the floor was opened by the chairman Mezzetto, he invited Rubbia to start the discussion.
Rubbia said it’s a pity that we do not have a US view of the situation here. Therefore he will remain on the questions in Europe. In his view, there is a very serious problem there. It reminds him of something that already happened when CERN asked itself what to do after the PS. Every European machine was coming up with proposals for 40 GeV machines. Then CERN became the only European entity. Only Weisskopf could argue for that kind of solution. This points to all European countries working together for a single big project. With EPPAC we are missing a great opportunity to join forces.
Another point is HK versus DUNE. It is clear to Rubbia that there are various questions with DUNE. Will it compete time-wise with HK, which uses well-oiled technology. Also the question of funding is a key: how much money is there available to do DUNE ? INFN can give 20 million euros to DUNE, but that is just a drop in the sea. So the question is, do we need two experiments competing with each other, or is one enough ? Because the need for two experiments is not clear.
Mezzetto said that the absence of the US was his fault as he was unable to convince Nigel Lockyer to come. Similarly for the Russians.
Masiero said that the whole purpose of APPEC, and the reason why in 2001 the president and directors of the major agencies in Europe decided to sit together at a table was the need to coordinate a coherent action. Considering the US, Japan etcetera, there is one single source of funding, or two. In Europe there are many. Rubbia countered that there is CERN. Masiero explained that there is no natural center of mass for astroparticle physics. As each agengy has to answer its own ministers, and there is no common body in Europe for this kind of research, it becomes hard to find a common intent. For the future, to have the famous large experiments for dark matter or double-beta decay, it becomes necessary for the agencies to find an agreement.
As for the second question, Masiero reminded that the main source of funding is coming from outside Europe, so the effort is to see how to complement the action of other agencies and sources. At the moment it is not clear that one experiment can be enough. We have redundancy, but we are facing a formidable challenge from the experimental results we want to achieve.