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

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Differential cross sections are presented for the production of pions, kaons, protons, and antiprotons at the angles 0° and 5.7°, produced in proton collisions with H2, Be, and Pb targets at primary momenta of 18.8 and 23.1 GeV/c, and in some cases at 8.65 and 11.8 GeV/c. The data are discussed with special reference to the role of isobar excitation in the production of secondary particles. All qualitative features of the experimental data are shown to be consistent with a dominant role of isobar decay in the production of pions, positive kaons, and protons at small angles. Excitation of isobars is shown to proceed without exchange of isospin between the colliding nucleons. Direct excitation of strange isobars can be ruled out. Evidence is presented for reduced probability of isobar production at 0°.

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.

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