The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3-4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from 1098-4402͞99͞2(8)͞081001(73)$15.00 © 1999 The American Physical Society 081001-1 PRST-AB 2 CHARLES M. ANKENBRANDT et al. 081001 (1999) a heavy-Z target and proceeding through the phase rotation and decay (p ! m n m ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact highenergy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

A conceptual design is prcscnted for a high power cuproiiickcl pion production target. It lorins a circular h~irid in a horizontal planc with apprnxiinatc dinicasioos of: 2.5 meters radios, 6 cin high and 0.6 cm thick. Thc target is continuously rotated at 3 i d s to carry hcat away from thc production rcgion to a water cooling channel. Bunches n l 16 CicV protons with total ciiergics oi270 kJ and repclition rates of 15 Hz arc incident leiigcritiiilly to arc of tlic targct along the symmetry axis of 21 20 liesla solcnoidal magnetic capture chanticl. The mechanical layout and cooling sctup arc dcscrihcd. lhults are prcseiitcd frnm realistic MAUS Moiitc Cmlo computcr simulatioiis o l thc pinn yield and encrgy dcpnsition in the targct. ANSYS finite clcment calcnlations arc beginning to givc predictions for tlic resultant shock heating stresses.

We report initial results of exposing low-Z solid and high-Z liquid targets to 150-ns, 4 × 10 12 proton pulses with spot sizes on the order of 1 to 2 mm. The energy deposition density approached 100 J/g. Diagnostics included fiberoptic strain sensors on the solid target and high-speed photography of the liquid targets. This work is part of the R&D program of the Neutrino Factory and Muon Collider Collaboration.

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