The ultimate goal of HIDDeN was to focus on revealing the (a)symmetries that had yet to be discovered—hence, hidden (a)symmetries—and the particles on which they acted, in particular those in the invisible sector, made up of neutrinos, dark matter, and other elusive components.
Although much had been discovered about what Nature was made of, most of the Universe and its workings remained hidden: Neutrinos are the most abundant known fermions in the Universe, but the reasons why they have mass and mixed remain unexplained; there is evidence of Dark Matter (DM), but it is still unknown which particle constituted it; particles and antiparticles behave differently (the so-called CP-violation) without a compelling reason; it is observed that, to a very large extent, only baryons exist in the Universe and not antibaryons, but the reason for this, and for why the Universe has not simply transformed into a gigantic cloud of photons, remained unclear; Dark Energy dominates the energy balance of the Universe, but its nature is still far from understood.
These questions cannot not be answered within the commonly accepted picture of particles and interactions—the Standard Model (SM)—and represent the first (and so far only) evidence that the SM needs to be extended to a more fundamental theory containing new particles and interactions. The ultimate mission of HIDDeN is to uncover the hidden sectors implied by the existence of non-zero neutrino masses, DM, and the baryon asymmetry, and to develop the New Standard Model of particles and interactions. HIDDeN made very significant advances in answering this questions, providing new theoretical and experimental developments and obtaining important scientific results. The strong dissemination strategy of the project increased the impact of the project. HIDDeN has been able to attract highly talented young people to a research career at the forefront of scientific and technological developments, has helped them to develop their full potential via a structured and coherent training and has fostered their growth as individuals.
The consortium consisted of 12 Beneficiaries from 5 EU Member States and one Associated country (Switzerland) with 25 Partner Organizations of which 13 world-leading scientific institutions, including the two leading particle physics laboratories, CERN and Fermilab, 5 Universities and Institutes from Developing Countries and 8 Private sector enterprises. The beneficiaries (partners) included 85 (>70) senior members and 46 postdocs (>30).
