Support for U.S. Consortium on MICE: The International Muon Ionization Cooling Experiment

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This proposal requests support for a U.S. university-based contribution to the Muon Ionization Cooling Experiment (MICE) being carried out at the Rutherford Appleton Laboratory (RAL) in the U.K. Recent discoveries in the study of neutrinos suggest that a very intense neutrino source, or "Neutrino Factory," might answer fundamental questions of particle physics and cosmology. This large future scientific project could be sited at an existing U.S. laboratory. MICE is an essential step towards this goal and will validate Neutrino Factory cost estimates by confirming the feasibility and performance of the key "muon cooling" technique. Neutrinos were originally postulated as massless neutral particles emitted during beta decay of radioactive nuclei. When they were found to come in two (and, later, three) types, each type was assumed (based on observation) to be immutable. However, recent experimental results indicate that over sufficiently long distances, neutrinos oscillate from one kind into another. From this, it follows that neutrinos have nonzero masses. This discovery raises fundamental issues regarding the total amount of matter in the universe and the origin of the excess of matter over antimatter, and places a high priority on studies to deduce the parameters of neutrino oscillation, including possible Charge conjugation-Parity (CP) violation in neutrino mixing. Although neutrino-oscillation studies using accelerator-derived neutrino beams are now planned or under way, recent world-wide R&D work points to a Neutrino Factory, producing a novel neutrino beam via decay of an intense muon beam circulating in a storage ring, as the ideal tool for neutrino oscillation and CP-violation studies. Such a tool would permit sensitivity several orders of magnitude beyond that of current and planned experiments. A Neutrino Factory would also be the first step towards muon-muon colliders in the longer term, with unique potential for studies of lepton collisions at the postulated Higgs resonance and the energy frontier. Muon beams at the required intensity can only be produced into a large phase space, but affordable existing acceleration technologies require a small input beam. This mismatch could be alleviated by "cooling" the muon beam to reduce its size. This is the goal of MICE and an international collaboration has been organized to carry it out. Broader impacts of this research include validation of an important new technique applicable in a variety of scientific and technological areas, including particle physics and cosmology; development of next-generation instrumentation; collaboration of interdisciplinary and international university and national-laboratory groups including accelerator and particle physicists and engineers; training of graduate and undergraduate students including those from community colleges and underrepresented minorities; and wide information dissemination via outreach activities and public media.