International Design Study for the Neutrino Factory (The IDS-NF Collaboration) Interim Design Report
The starting point for the International Design Study for the Neutrino Factory (the IDS-NF) was the output of the earlier International Scoping Study for a future Neutrino Factory and super-beam facility (the ISS). The accelerator facility described in section 2 incorporates the improvements that have been derived from the substantial amount of work carried out within the Accelerator Working Group. Highlights of these improvements include: • Initial concepts for the implementation of the proton driver at each of the three example sites, CERN, FNAL, and RAL; • Detailed studies of the energy deposition in the target area; • A reduction in the length of the muon beam phase-rotation and bunching systems; • Detailed analyses of the impact of the risk that stray magnetic field in the accelerating cavities in the ionisation cooling channel will reduce the maximum operating gradient. Several alternative ionisation-cooling lattices have been developed as fallback options to mitigate this technical risk; • Studies of particle loss in the muon front-end and the development of strategies to mitigate the deleterious effects of such losses; • The development of more complete designs for the muon linac and re-circulating linacs; • The development of a design for the muon FFAG that incorporates insertions for injection and extraction; and • Detailed studies of diagnostics in the decay ring. Other sub-systems have undergone a more “incremental” evolution; an indication that the design of the Neutrino Factory has achieved a degree of maturity. The design of the neutrino detectors described in section 3 has been optimised and the Detector Working Group has made substantial improvements to the simulation and analysis of the Magnetised Iron Neutrino Detector (MIND) resulting in an improvement in the overall neutrino-detection efficiency and a reduction in the neutrino-energy threshold. In addition, initial consideration of the engineering of the MIND has generated a design that is feasible and a finite element analysis of the toroidal magnetic field to produce a realistic field map has been carried out. Section 3 also contains, for the first time, a specification for the near-detector systems and a demonstration that the neutrino flux can be determined with a precision of 1% through measurements of inverse muon decay at the near detector. The performance of the facility, the work of the Physics and Performance Evaluation Group, is described in section 1. The effect of the improved MIND performance is to deliver a discovery reach for CP-invariance violation in the lepton sector, the determination of the mass hierarchy, and of θ 13 that extends down to values of sin 2 2θ 13 ∼ 5 × 10 −5 and is robust against systematic uncertainties. In addition, the improved neutrino-energy threshold has allowed an indicative analysis of the kind of re-optimisation of the facility that could be carried out should θ 13 be found close to the current upper bound. The results presented in section 1 demonstrate that the discovery reach as well as the precision with which the oscillation parameters can be measured at the baseline Neutrino Factory is superior to that of other proposed facilities for all possible values of sin 2 2θ 13 .