Search Results (33 total)

Neutrino factory and muon collider cooling lattices require both high gradient rf cavities and strong focusing solenoids. Experiments have shown that there may be serious problems operating rf in the required magnetic fields. Experimental observations using vacuum rf cavities in magnetic fields are discussed, current published models of breakdown with and without magnetic fields are briefly summarized, and some of their predictions compared with observations. A new theory of magnetic field dependent breakdown is presented. It is proposed that electrons emitted by field emission on asperities on one side of a cavity are focused by the magnetic field to the other side where they induce mechanical fatigue leading to cavity surface damage in small spots. Metal is then electrostatically drawn from the molten spots, becomes vaporized and ionized by field emission from the remaining damage, and causes breakdown. The theory is fitted to existing 805 MHz data and predictions are made for performance at 201 MHz. The model predicts breakdown gradients significantly below those specified for either the International Scoping Study neutrino factory or a muon collider. Possible solutions to these problems are discussed, including designs for magnetically insulated rf in which the cavity walls are designed to be parallel to chosen magnetic field contour lines and consequently damage from field emission is expected to be suppressed. An experimental program that could study these problems and their possible solution is outlined. We also mention the use of high pressure gas as an alternative possible solution.

We explore a practical approach for designing ionization cooling channels with periodic solenoidal focusing. We examine the lattice characteristics in terms of the properties of the coils and the cell geometry. The peak magnetic field in the coils is an important engineering constraint in lattice design. We examine the dependence of the peak field, momentum passband locations, and the beta function on the coil parameters. We make a systematic examination of all allowed lattice configurations taking into account the symmetry properties of the current densities and the beta function. We introduce a unique classification for comparing cooling lattice configurations. While solutions with a single coil per cell illustrate most of the effects that are important for cooling channel design, the introduction of additional coils allows more flexibility in selecting the lattice properties. We look at example solutions for the problem of the initial transverse cooling stage of a neutrino factory or muon collider and compare our results with the properties of some published cooling lattice designs. Scaling laws are used to compare solutions from different symmetry classes.

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.

Differential cross sections are presented for the inclusive production of charged pions in the momentum range 0.1–1.2 GeV/c in interactions of 12.3 and 17.5 GeV/c protons with Be, Cu, and Au targets. The measurements were made by Experiment 910 at the Alternating Gradient Synchrotron (AGS) at Brookhaven National Laboratory. The cross sections are presented as a function of pion total momentum and production polar angle θ with respect to the beam.

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)].

The weak nucleon axial-vector (F_A) and vector (F_V) form factors are determined from the momentum-transfer-squared (Q²) distributions using 2538μ^-p and 1384μ^-Δ⁺⁺ events. The data were obtained from 1 800 000 pictures taken in the BNL 7-foot deuterium-filled bubble chamber exposed to a wide-band neutrino beam with a mean energy E_ν=1.6 GeV. In the framework of the conventional V-A theory with standard assumptions, the value obtained from the μ^-p events for the axial-vector mass M_A in the pure dipole parameterization is 1.070^+0.040_-0.045 GeV and from the μ^-Δ⁺⁺ events is 1.28^+0.08_-0.10 GeV. These results are in good agreement with an earlier measurement from this experiment and other recent results. The reaction mechanisms for both processes are compared and found to be very similar. A two-parameter fit for the quasielastic reaction, using dipole forms for F_V and F_A yields M_A=0.97_-0.11^+0.14 GeV and M_V=0.89_-0.07^+0.04 GeV, which is in good agreement with the conserved-vector-current value of M_V=0.84 GeV. Possible deviations from the standard assumptions are also discussed.

A total of 22 muon-neutrino-electron elastic-scattering events (ν_μe→ν_μe) have been observed in an exposure of the Fermilab 15-foot bubble chamber filled with a heavy neon-hydrogen mixture to a wide-band neutrino beam. The elastic-scattering cross section is measured to be 1.67±0.44×10^-42E_ν cm² GeV^-1. The value of the weak mixing angle (sin²θ_W) determined from this cross section, which is consistent with other measurements of this angle, is 0.20_-0.05^+0.06.

High-statistics data from two exposures of the BNL 7-foot deuterium bubble chamber to a wide-band-neutrino beam with an average energy of 1.6 GeV were analyzed for exclusive pion production in charged-current neutrino-deuterium interactions. For the single-pion production reactions, the properties of Δ⁺⁺ production and decay as well as the final results of an isospin analysis are presented. New results for single-pion and multipion production are also presented.

We report a study of strange-particle production from 61?0 charged-current ν_μNe interactions in the Fermilab 15-ft bubble chamber. The observed sample consists of 2279 K⁰, 1843 Λ (including 94 Σ⁰), 93 Λ¯, and 4 Ξ^-. We give inclusive production rates for each of these, as well as the rates for specific single-, double-, and triple-vee channels. From these we derive the rates for associated production of ss¯ quark pairs, and for single-s-quark production via charm decay. The dependence of K⁰ and Λ production on E_ν, Q², W², x_B, and y_B are given. Normalized distributions of Feynman x, rapidity, fragmentation variable z, and transverse momentum squared are obtained for K⁰ and Λ, and compared with those for charged pions. QCD predictions on the behavior of 〈P_T ²〉 are tested.

We have searched for the production of like-sign dilepton events (ν_μ+Ne→μ^-+e^-+…) in a wide-band neutrino beam at Fermilab using the 15-ft bubble chamber. We observe no signal above the background arising from conventional sources. We set 90%-confidence-level upper limits for the production rates of (ν_μ+Ne→μ^-+e^-+…) / (ν_μ+Ne→μ^-+…)<~0.76×10^-4 and (ν_μ+Ne→μ^-+e^-+…) / (ν_μ+Ne→μ^-+e⁺+…)<~5.3×10^-2.

We report on a high-statistics bubble-chamber experiment using the Fermilab 15-ft bubble chamber filled with a heavy neon/hydrogen mixture exposed to a wide-band neutrino beam. In a sample of 106 000 ν_μ &>0.3 GeV/c) and a negative muon were observed. After corrections, the rate for opposite-sign dilepton production for ν_μ charged-current events is (0.52±0.09)%. The E_ν dependence of this rate from threshold to ≊200 GeV is presented. The kinematic distributions and strange-particle content of the dilepton events are consistent with those expected from charm-particle production in neutrino interactions. A total of 58 neutral strange particles (Λ→pπ^-, K_S⁰→π⁺π^-) are observed in these events, where less than 16 are expected from conventional charged-current interactions. The presence of a significant excess of Λ’s is evidence for substantial charmed-baryon production.

We have measured the cross-section ratio R=σ(νpπ^-) / σ(μ^-pπ⁺)=0.11±0.023, 0.13±0.023, 0.15±0.025 for M_pπ<1.4, 1.6, 2.0 GeV, respectively, in the energy range 0.4<E_ν<3.0 GeV. The data are consistent with various weak one-pion production models incorporating the Weinberg-Salam structure of neutral currents.

The total cross sections for ν_μn and ν_μp charged-current interactions and their ratio R=σ_T(νn) / σ_T(νp) have been measured as a function of neutrino energy from 0.4 to 10 GeV. The experiment is performed using the BNL 7-foot deuterium bubble chamber exposed to the Alternating Gradient Synchrotron wide-band neutrino beam. The absolute values of the cross sections are normalized to the quasielastic scattering (ν_μn→μ^-p) cross section. Above 1.6 GeV the data are consistent with the quark-parton model. We find that σ_T(νn) / E_ν=(1.07±0.05)×10^-38, σ_T(νp) / E_ν=(0.54±0.04)×10^-38, and σ_T(νN) / E_ν=(0.80±0.03)×10^-38 cm²/GeV for 〈E_ν〉=3.2 GeV, and R=1.95±0.10 for 〈E_ν〉=3.7 GeV.

Strange-particle production in charged-current and neutral-current neutrino interactions has been studied using the BNL 7-foot deuterium bubble chamber. A total of 37 charged-current and 9 neutral-current events in the data sample contain one or more strange particles. Three events have ΔS≠0. The measured total rate for neutral V⁰ production in charged-current interactions is (4.2±1.0)%. Cross sections are given for low-multiplicity reactions involving neutral strange particles.

A search for neutrino oscillations in a wide-band neutrino beam at Fermilab with use of the 15-ft bubble chamber is reported. No evidence is found for neutrino oscillations and upper limits are set on the mixing angles and neutrino mass differences in the transitions ν_μ→ν_e, ν_μ→ν_τ, and ν_e→ν_^∼e, where ∼e denotes "not e."

The quasielastic reaction ν_μn→μ^-p was studied in an experiment using the BNL 7-foot deuterium bubble chamber exposed to the wide-band neutrino beam with an average energy of 1.6 GeV. A total of 1138 quasielastic events in the momentum-transfer range Q²=0.06-3.00 (GeV/c)² were selected by kinematic fitting and particle identification and were used to extract the axial-vector form factor F_A(Q²) from the Q² distribution. In the framework of the conventional V-A theory, we find that the dipole parametrization is favored over the monopole. The value of the axial-vector mass M_A in the dipole parametrization is 1.07±0.06 GeV, which is in good agreement with both recent neutrino and electroproduction experiments. In addition, the standard assumptions of conserved vector current and no second-class currents are checked.

The isospin structure of weak single-pion production in the reactions νp→μ^-pπ⁺, νn→μ^-pπ⁰, and νn→μ^-nπ⁺ has been studied using the 7-foot deuterium bubble chamber exposed to a wide-band neutrino beam at BNL. We find that the I=1 / 2 Nπ amplitude is substantial even in the Δ(1232) mass region and the relative phase angle ψ is approximately 90° as predicted by the Adler model.

Correlations of two π⁰ mesons with transverse momenta p_T up to 13 GeV/c have been measured with large azimuthal acceptance. Results for cross sections, p_out, and z distributions are compared in detail with models based on two-constituent scattering and fragmentation. The width of the constituent transverse-momentum Gaussian distribution would have to be doubled to match that from experiments with p_T below 5 GeV/c. A more likely explanation is the presence of processes with more than two constituents in the final state.

In a broadband neutrino exposure of the Fermilab 15-ft bubble chamber, we observe the production of the Σ_c⁺⁺(2426) charmed baryon followed by its decay to Λ_c⁺(2260) and π⁺. We find the mass of the Λ_c⁺ to be 2257±10 MeV and the m(Σ_c⁺⁺)-m(Λ_c⁺) mass difference to be 168±3 MeV. Previously unseen two-body decay modes of the Λ_c⁺(2260) are observed.

We have observed 34 events with visible strange-particle production out of a total charged-current sample of 4500 events in a wide-band neutrino exposure of the Brookhaven National Laboratory 7-ft bubble chamber filled with H₂ or D₂. Three events were uniquely identified as having single-strange-particle production, two with ΔS=-ΔQ. In both ΔS=-ΔQ events we observe the Λ_c⁺(2260), which in one case decays to Λπ⁺π⁺π^- and in the second case to pK̅ ⁰π^-π⁺. Production rates are given.

We have observed eleven events of the reaction ν_μe^-→ν_μe^- in a sample of 106 000 charged-current neutrino interactions in a heavy neon-hydrogen mixture in the 15-ft. bubble chamber at Fermilab. We obtain a cross section for this process of [(1.8±0.8)×10^-42 cm²/GeV]E_ν. This result is in good agreement with the prediction of the Weinberg-Salam model with sin²θ_W=0.2.

We have observed the production of the D⁰ meson by neutrinos followed by the decay D⁰→K_S⁰+π⁺+π^-. Correcting for detection efficiencies and K⁰ decay branching ratios, we find that the production of the D⁰ followed by decay into K⁰π⁺π^- corresponds to (0.7 ± 0.2)% of all charged-current neutrino interactions.

We have studied correlations between two π⁰'s produced at the CERN intersecting storage rings, utilizing detectors with large azimuthal acceptance. We find that the previously observed enhancement of two π⁰'s produced at azimuthal difference near 180° can be made to vanish when certain kinematic effects are removed. However, we observe aligned configurations above 8 GeV of transverse energy unexplained by such kinematic effects.

We present upper limits on the production of heavy leptons (L^±) by neutrinos via the process ν_μ+Ne→L^±+⋯, L^±→e^±+ν+ν̅ . These limits imply that the L^- and L⁺, if they couple in full strength to ν_μ, are heavier than 7.5 and 9 GeV, respectively. They also imply that the coupling strength ν_μ to the recently discovered 1.9-GeV heavy lepton τ is less than 0.025 of the normal ν_μ-μ coupling.