Search Results (32 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.

An analysis of inclusive pion production in proton-beryllium collisions at 6.4, 12.3, and 17.5 GeV/c proton beam momentum has been performed. The data were taken by Experiment 910 at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. The differential π⁺ and π^- production cross sections (d²σ/dpdΩ) were measured up to 400 mrad in θ_π and up to 6 GeV/c in p_π. The measured cross section was fit with a Sanford-Wang parametrization.

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.

There have been active efforts in the U.S., Europe, and Japan on the design of a neutrino factory. This type of facility produces intense beams of neutrinos from the decay of muons in a high-energy storage ring. In the U.S., a second detailed feasibility study (FS2) for a neutrino factory was completed in 2001. Since that report was published, new ideas in bunching, cooling, and acceleration of muon beams have been developed. We have incorporated these ideas into a new facility design, which we designate as study 2B (ST2B), that should lead to significant cost savings over the FS2 design.

Practical ionization cooling rings could lead to lower cost or improved performance in neutrino factory or muon collider designs. The ring modeled here uses realistic three-dimensional fields. The performance of the ring compares favorably with the linear cooling channel used in the second U.S. Neutrino Factory Study. The normalized 6D emittance of an ideal ring is decreased by a factor of approximately 240, compared with a factor of only 15 for the linear channel. We also examine such real-world effects as windows on the absorbers and rf cavities and leaving empty lattice cells for injection and extraction. For realistic conditions the ring decreases the normalized 6D emittance by a factor of 49.

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)].

Transverse ionization cooling of muons is modeled as a Brownian motion of the muon beam as it traverses a Li or Be rod. A Langevin-like equation is written for the free particle case (no external transverse magnetic field) and for the case of a harmonically bound beam in the presence of a focusing magnetic field. We demonstrate that the well-known muon cooling equations for short absorbers can be extrapolated to the useful case of a long absorber rod with a focusing magnetic field present.

The requirements for the generation of forward directed Smith-Purcell emission from relativistic electrons are introduced, and the first experimental evidence of this phenomenon is presented. The experiments were conducted with a 2.8 MeV/ c electron beam interacting with a 1 cm period grating. Radiation emitted in two bands with wavelengths ranging from 600 to 650 μm and 1.2 to 1.7 mm were measured. Grating period to wavelength ratios were as high as 16. The measured intensities are higher than that predicted by incoherent emission.

A 580-MW peak power, radially polarized CO₂ laser beam (λ=10.6 μm) focused by an axicon accelerated 40-MeV electrons by ≤3.7 MeV over a 12-cm interaction length (31 MeV/m), using the inverse Cherenkov effect in which a gas is used to slow the light wave. This represents the first direct observation of acceleration using this effect and demonstrates the effectiveness of the radially-polarized-axicon-focused geometry. The observed energy gain agrees with model predictions.

We have measured the analyzing power in π⁺, π^-, and K_S⁰ production by a polarized proton beam at 13.3 and 18.5 GeV/c. The data cover the central and the beam fragmentation region, in the transverse-momentum range up to 2 GeV/c. The results indicate that sizable effects are present at high x_F and also persist into the hard-scattering region for K_S⁰ and π⁺. A zero value of the analyzing power was observed for π^- production.

We have measured the polarization P, the analyzing power A, and the polarization transfer D of Σ⁰’s produced inclusively by a polarized proton beam at 18.5 GeV/c. Our data cover a region of moderate p_T (average 1 GeV/c) and Feynman x up to 0.75. We find agreement with a previous measurement of the Σ⁰ polarization P. We observe nonzero values for A and D, but they are significantly smaller than predictions based on a simple parton-recombination model. We have extended this model to include finite transversity spin flips, which improves agreement with the data considerably.

The Brookhaven Alternating Gradient Synchrotron polarized proton beam incident on a beryllium target was used for inclusive Λ production at beam momenta of 13.3 and 18.5 GeV/c. The beam polarization was transverse to the beam direction with magnitude 0.63 at 13.3 GeV/c and 0.40 at 18.5 GeV/c. The Λ polarization was measured and found to be in agreement with results from earlier experiments which used unpolarized proton beams. Analyzing power A_N and spin transfer D_NN of the Λ’s were both measured and compared with a hyperon-polarization model in which the polarization arises from a Thomas-precession effect. There is good agreement with its predictions: A_N=0 and D_NN=0. In particular, our measurement of 〈D_NN〉=-0.009±0.015 supports the idea that the valence quarks carry all of the hadron spin, since this assumption is implicit in the model’s use of SU(6) wave functions to form final-state hadrons from beam fragments and sea quarks. The presence of substantial K_S samples at both beam momenta and Λ¯’s at 18.5 GeV/c prompted a measurement of their analyzing powers, which yielded A_N(K_S)=-0.094±0.012 at 13.3 GeV/c beam momentum and -0.076±0.015 at 18.5 GeV/c, and A_N(Λ¯)=0.03±0.10.

We have measured the polarization of Λ’s inclusively produced by the polarized proton beam at the Brookhaven Alternating Gradient Synchrotron at 13.3 and 18.5 GeV/c. Data were taken in the central and beam-fragmentation region with hyperon transverse momenta from 0.4 to 2.5 GeV/c. The Λ polarization parameter P is found to be large in agreement with earlier data at other energies. The analyzing power A_N and spin transfer D_NN are nearly zero in the same kinematic region, as predicted by certain models of particle production.

A Dalitz-plot analysis of 620 E(1420) events was performed on the reaction p¯p→(K_S⁰K⁺π^-)X at 6.6 GeV/c, obtained at the Brookhaven National Laboratory Multiparticle Spectrometer facility. The mass and width of the E(1420) peak are 1424±3 and 60±10 MeV, respectively. The best fit to the E(1420) is a J^PG=0^-+ state with a substantial δπ decay mode, produced over a large nonresonant background of 1⁺⁺ K^*K and phase space. This fit shows the same characteristics as the E(1420) observed in our companion π^-p experiment.

A search for narrow states with baryon number zero and strangeness -1 was conducted in p―p collisions. These hypothetical states could be composed of two quarks and two antiquarks and are similar to baryonium states. The experiment studied the missing mass recoiling against a slow K⁺. No narrow resonances were observed, corresponding to cross-section upper limits of 4 μb for masses below 2.75 Gev/c².

Ξ^*- production was studied in the reaction K^-+p→K⁺_slow+X^- at 5 GeV/c. The slow K⁺ was electronically detected, while the X^- was observed as a missing mass, thus allowing for observation of all Ξ^* independent of decay mode. The observed Ξ states were Ξ(1320), Ξ(1530), Ξ(1820), Ξ(2030), Ξ(2250), Ξ(2370), and Ξ(2500). These data establish and confirm the existence of Ξ(2250) and indicate a peculiar production-cross-section behavior for the Ξ^*(2370).

A high-statistics search for the production of narrow p̅ p states with a p̅ beam at 5 GeV/c finds no evidence for such states from threshold up to 2.3 GeV. In particular, we set an upper limit (95% C.L.) of 9 nb for any state below 1.95 GeV with Γ≤5 MeV in the reaction p̅ p→p̅ pπ⁰. Comparable limits are set for the reaction p̅ p→p̅ p(ρ+ω) and inclusive p̅ p production.

The invariant differential cross sections and polarization (0.5<x_F<0.8, 0.0<p_⊥<1.5 GeV/c) of Λ's produced in pion-induced reactions have been measured. The scaling cross section agrees with previous experiments performed at other energies. The (1-x_F)^N dependence of the cross section gives an exponent of N=1.88±0.04. These are the first polarization measurements in the pion fragmentation region. A mean polarization of (-5.3 ± 1.2)% is observed with no trend toward large negative polarization with increasing transverse momentum.

We measured the differential cross section for proton-proton elastic scattering at 6 GeV/c, with both initial spins oriented normal to the scattering plane. The analyzing power A shows significant structure with a large broad peak reaching about 24% near P_⊥²=1.6 (GeV/c)². The spin-spin correlation parameter A_nn exhibits more dramatic structure, with a small but very sharp peak rising rapidly to about 13% at 90°_c.m.. This sharp peak may be caused by particle-identity effects.

A search for production of D^*-'s using the decay chain D⁰π^-, D⁰→K⁺π^-, was carried out at the Brookhaven National Laboratory multiparticle spectrometer with a 16-GeV/c π^- beam and a hydrogen target. At 95% confidence level the upper limits for the product of peripheral production cross section by branching ratio are 2.4 nb for inclusive D^*- production and 1.3 nb for the exclusive channel π^-p→D^*-Λ_c.

We have performed a high-statistics search for narrow meson states (Γ<~30 MeV) produced in π^-p interactions at 16 GeV/c and decaying into pp̅ π⁺ or Λp̅ π^±. This is the first systematic search in channels requiring exchange of exotic mesons. The cross section for production of such states is ruled out at the 95% confidence level with upper limits ranging from ∼10 nb at 2.3 GeV to ∼40 nb at 2.8 GeV.

The energy dependence of the spin-parallel and spin-antiparallel cross sections for p_↑+p_↑→p+p at 90°_c.m. was measured for beam momenta between 6 and 12.75 GeV/c. The ratio (dσ / dt)_parallel:(dσ / dt)_antiparallel at 90° is about 1.2 up to 8 GeV/c and then increases rapidly to a value of almost 4 near 11 GeV/c. Our data indicate that this ratio may depend only on the variable P_⊥², and suggests that the ratio may reach a limiting value of about 4 for large P_⊥².

We measured dσ / dt for p_↑+p_↑→p+p from P_⊥²=4.50 to 5.09 (GeV/c)² at 11.75 GeV/c. We used a 59%-polarized proton beam and a 71%-polarized proton target with both spins oriented perpendicular to the scattering plane. In these large-P_⊥² hard-scattering events, spin effects are very large and the ratio (dσ / dt)_↑↑:(dσ / dt)_↑↓ grows rapidly with increasing P_⊥², reaching a value of 4 at 90° (c.m.). Thus, hard elastic scattering, which is presumably due to the direct scattering of the protons' constituents, may only occur when the two incident protons' spins are parallel.