Search Results (4 total)

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 high-energy 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.

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 a heavy-Z target and proceeding through the phase rotation and decay (π→μν_μ) 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 Workshop [R. B. Palmer, A. Sessler, and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].

An extensive experimental study of fluctuation effects in the complex ac impedance Z_W(ω,T) of one-dimensional tin-whisker crystals near the superconducting transition temperature T_c is described. The behavior of Z_W(ω,T) in <001> whiskers with cross-sectional areas 2 × 10^-10-3 × 10^-9 cm² was measured at 60 MHz, 1 kHz, and dc from below T_c in the mean-field temperature range up through T_c and slightly above. Paraconductivity data were not obtained. By correlating high-frequency reactance data with resistance data from dc or low-frequency ac measurements, a more stringent test was made of the theory of fluctuation effects than is possible with dc measurements alone. We find that the theory of Langer and Ambegaokar (LA) as completed by McCumber and Halperin (MH) for the onset of resistance is inconsistent with our results unless the LA barrier height is reduced by a factor of approximately 0.55. If this is done, the LA-MH prediction agrees with resistance data over the full whisker size range. The MH result for the onset of fluctuation effects in the reactance agrees with our data without modification. No theory exists which can explain the behavior of Z_W(ω,T) as T passes through T_c. Our data are presented in a form to facilitate comparison with future theories. Reactance data in the mean-field region yield a direct measurement of the penetration depth. We find an interesting size effect in this quantity, and a new value is reported for the London penetration depth in pure tin, λ_L=289±20 Å.

The spin-lattice relaxation time T₁ of F¹⁹ has been measured in a pure BaF₂ crystal over a temperature range of 300 to 1150°K and in a BaF₂ crystal containing 4.9×10¹⁹ ions/cm³ of Eu³⁺ from 4.2 to 1000°K. The measurements were made at 29 MHz using the magnetic-recovery method with the magnetic field along the [111] and [100] crystallographic directions. The electronic relaxation time τ_e of the europium was also measured at 9.5 gHz at 4.2, 63, 77, and 90°K. The data indicate that the diffusion of F^- ions provides the predominant relaxation mechanism above 700°K in the pure sample and above 500°K in the doped one. The minimum in the high-temperature segment of the T₁-versus-T curve appears at 990°K for pure BaF₂ and at 800°K for doped BaF₂. These yield jump frequencies of ν_F(vacancy)=1.3×10¹⁵exp(-1.35 eV/kT) and ν_F(interstitial)=6.5×10¹¹exp(-0.62 eV/kT); to our knowledge these have never been measured before. Below 500°K the nuclear relaxation is due to paramagnetic impurities. The orientation dependence of T₁ indicates that the transition from "diffusion limited" (DL) to "rapid diffusion" (RD) relaxation occurs between 50 and 70°K in the doped sample. In the DL range, we find good agreement between the observed T₁ of F¹⁹ and the T₁ values calculated from τ_e, whereas at 4.2°K, which lies in the RD range, the calculated value is 300 times larger than the observed one. Our low-temperature T₁ data yield 5.6×10^-14 cm/sec for the spin-diffusion constant D.