Search Results (14 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)].

We observe no A₂^± production in π^±p collisions near threshold. Because our upper limits for the A₂ cross-section limit s-wave production, the rapid rise of the cross section from threshold observed by other experiments must be due to p-wave production. Discussion of this result and a comparison to the data of Binnie et al. are given.

Analyses of measurements of muons produced directly, in the forward direction, by the interaction of 28-GeV protons with uranium show that the muon/pion production ratio for negative particles is 13×10^-5 for 11.6-GeV particles, 2.6×10^-5 at 20.3 GeV, 1.3×10^-5 at 23.5 GeV, and 7.0×10^-6 at 25 GeV. The largest ratio is similar to ratios measured at higher energies and large transverse momenta and none of the ratios are easily explained in terms of conventional mechanisms.

We present here the results of an experiment to study the polarization in p-p elastic scattering at the incident momenta 5.15, 7.00, and 12.33 Ge V/c, at t values ranging between - 0.5 and - 6.5 (GeV/c)². At each momentum we observe a relative maximum in the polarization around t=-1.8 (GeV/c)². At 12.33 GeV/c the data exhibit a double zero near t=-2.4 (GeV/c)² and another relative maximum near t=-2.9 (GeV/c)². The results are discussed in terms of the Chu-Hendry optical model.

We report here the results of an experiment which studies the polarization of the recoil proton in the inclusive reaction π^±p→pX^± at 4 GeV / c, where M_x varies from 1200 to 1450 MeV, and t varies from -0.2 to -0.8 (GeV / c)². The recoil proton was identified by its time of flight and its momentum, as determined by a wire-chamber magnetic spectrometer. The polarization of the recoil proton normal to the scattering plane was measured with a wire-chamber carbon analyzer. Polarizations are presented as a function of mass M_x for all t and as a function of t for all masses. The typical error in the polarization is ± 0.1. A significant difference is observed in the behavior of the polarization associated with the X⁺ and the X^-. Possible implications of this disparity are explored.

We present herein the initial results of a large-angle elastic p-p polarization experiment which is now in progress at the Argonne ZGS (Zero-Gradient Synchrotron) accelerator. Data for the incident proton momentum of 5.15 GeV / c are presented for 30^∘≲θ_c.m.≲90^∘. These results, which extend to t≈-4.0(GeV / c)², represent the first high-statistics p-p polarization measurements for |t| values greater than ∼2.5 (GeV / c)². We observe a minimum in the polarization near t=-0.8(GeV / c)², a smooth increase in the polarization until a maximum is attained near t=-1.8(GeV / c)², and then a monotonic decline in the polarization until the value of zero is reached at θ_c.m.=90^∘. The data are analyzed in terms of an optical model.

Wire spark planes and scintillation counters were used in an experiment designed to measure the decay correlations among the products of the decay of stopped K⁺ mesons to a muon, a neutrino, and a pion, and to measure the polarization of the muon. The results determined the value of the form factor ratio to be ξ(0)=-0.57±0.24. The momentum dependence of the f₊ form factor was defined by our measured value of λ₊=0.027±0.019 (taking λ_-=0). From the analysis of the muon polarization, taking the values for λ₊ and λ_- found for the decay correlation analysis, the form factor ratio was measured to be ξ(0)=-0.64±0.27.

In the reaction π^-p→A₂^-p at 4 BeV/c, 474 rare A₂^-→K^-K_L⁰ decays were observed. The A₂ mass spectrum has a shape which is compatible with a simple Breit-Wigner resonance, although the dipole hypothesis cannot be ruled out. Assuming the A₂ has J^P=2⁺, an analysis of 318 events yields the following A₂ spin density matrix elements: ρ₀₀=0.24, ρ₁₁=0.38, ρ₂₂=0, and ρ_1-1=0.23. Thus the A₂^- is produced, in part, by unnatural spin-parity exchange.

The mass spectrum of charged A₂ mesons has been measured in the reaction π^±p→pX^± at 4 BeV / c. More than 3700 events per 5-MeV bin have been recorded at the A₂⁺ peak. More than 2600 events per 5-MeV bin have been recorded at the A₂^- peak. The standard deviation of the experimental resolution function is 3.9 MeV. The A₂⁺ and A₂^- mass spectra have shapes compatible with a simple Breit-Wigner resonance on a linear background.

We have measured the polarization of cosmic-ray muons arriving at seal level with different energies and from different zenith angles. The polarization of positive muons from the zenith with energies near 1.0 GeV was found to be -0.33 ± 0.04, where the polarization in the direction of flight was measured and the negative sign indicates that the spin was antiparallel to the direction of flight. Muons from the zenith with energies near 3.5 GeV at sea level had polarizations of -0.38 ± 0.04, and the polarization of muons with energies near 4.5 GeV incident at an angle of 45° with the zenith was found to be -0.34 ± 0.04. These polarizations are consistent with the polarizations calculated on the basis that the muons are derived almost wholly from the decay of pions produced by the interaction of primary and secondary cosmic-ray hadrons with the nuclei of the atmosphere.

A search for the vector boson (W particle), postulated as the mediator of the weak interaction, has been carried out by determining the intensity and polarization of muons originating very near the point of interaction of 28-GeV protons with nucleons. Bosons were not observed and the upper limit on the production cross section for W's with masses between 2.0 and 4.5 GeV / c² is Bσ_W≲6×10^-36 cm², where B is the branching ratio for the W decay to a muon and a neutrino. A comparison between the measured flux of muon pairs and the flux expected on the basis of a plausible model for the production and decay of both W's and heavy virtual γ's suggests that the experiment may not have been sensitive to W's, if they exist in this mass region. The flux of high-energy muons produced directly by an unknown process, an X process, is determined to be no greater than 10^-6 times the pion flux.

A search for the vector boson (W particle), postulated as the mediator of the weak interaction, has been carried out by determining the intensity and polarization of muons originating very near the point of interaction of 28-GeV protons with nucleons. Bosons were not observed and the upper limit on the production cross section for W's with masses between 2.0 and 4.5 GeV/c² is Bσ≲6×10^-36 cm², where B is the branching ratio for the W decay to a muon and a neutrino.

A systematic study has been made of the reactions pp→pp and pp→pN^* in the angular range from θ_lab=10^∘ to θ_c.m.=90^∘ at 3, 4, 5, 6, and 7 GeV / c. An orthogonal dispersion magnetic spectrometer detected protons from interactions in hydrogen with momentum transfer (-t) in excess of 0.5 (GeV)². Well-defined peaks in the missing-mass spectra occurred at average N^* masses of 1240±6, 1508±2, and 1683±3 MeV with average full widths of 102±4, 92±3, and 110±4 MeV, respectively. Below 2400 MeV no other significant enhancements were found. The N^* production cross sections dσ / dt near θ_c.m.=90^∘ are in qualitative agreement with the predictions of the statistical model. For each isobar the differential cross section at fixed energy varies as exp(-v / v₀), where v≡[-tu / (t+u)]; v₀ varies systematically with energy and tends toward the same value (≈0.4 GeV²) for each isobar at the upper limit of our energy range.