We consider here an entry level Muon Collider to operate as a Higgs Factory. No cost estimate has yet been prepared for this stage, so we mention here only the obvious “cost drivers.” First, the initial muon beam must be prepared as a single bunch of each charge. This may involve an additional ring for the proton driver to coalesce proton bunches into a single pulse. The cooling will have to be significantly augmented. First, a much lower transverse emittance is needed, and second, it will be necessary to provide emittance exchange to maintain a reasonable transmission of the muons. The additional cooling will permit going to smaller solenoids and higher frequency rf systems (402.5 or perhaps 805 MHz), which should lower the incremental cost somewhat. Next, we will need considerably more acceleration, though with smaller energy acceptance and aperture requirements than at present. Lastly, we will need a very low b* lattice for the storage ring, along with mitigation of the potentially copious background levels near the interaction point. In this case the detector is, in effect, part of the Collider and cannot be ignored in terms of its cost impact.

Of the items mentioned, it is likely that the additional cooling and the additional acceleration are the most significant cost drivers. Future work will define the system requirements better and permit a cost estimate of the same type provided for Studies-I and -II.