Search Results (30 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)].

Low-transverse-momentum photon production at the CERN ISR is compared in high- and low-multiplicity events. High-transverse-energy pp collisions and low-multiplicity αα and pp collisions are studied. Relative photon-to-charged-track production is found to be the same in pp minimum bias, αα minimum bias, and pp high-transverse-energy collisions, to within 15%. No low-P_T excess is seen; the limits are dominated by systematic uncertainties.

Relative yields of φ and charged K mesons are measured as functions of charged multiplicity in the central rapidity region for pp, dd, pα, and αα collisions at sqrt[s_NN]=3.15 and 44 GeV. No anomalous strange-particle production is observed in αα reactions relative to pp even at large multiplicities corresponding to events comprising less than 3.6×10^-4 of the inclusive cross section.

Rapidity and charge distributions have been measured for central charged tracks in events at center-of-mass energy 63 GeV, triggered on a π⁰ near 11° with transverse momentum greater than 2.25 GeV/c. The observed distributions are consistent with parton-parton scattering models with a spin-one gluon, and inconsistent with the exchange of a spin-zero gluon.

We have searched for the production of long-lived R-Δ⁺⁺ hadrons, which contain a gluino in addition to three up quarks, in pp, π⁺p, and K⁺p interactions at 147 GeV/c. For R-Δ⁺⁺'s of lifetime greater than 10^-9 sec, and laboratory momentum greater than 2 GeV/c, we place 90%-confidence-level upper limits of 6.1 μ b in pp collisions, 4.4 μ b in π⁺p, and 29 μ b in K⁺p.

Measurements of the central multiplicity associated with high-p_t particles up to 2 GeV/c in p-p, p-α, and α-α collisions, and measurements of dσ / dE_t are presented. The difference in associated multiplicity, n (p-α)-n(p-p), is independent of p_t while n (α-α)-n(p-p) rises with p_t, providing new information on the "anomalous" p_t dependence of nuclear inclusive cross sections.

From a study of 8-GeV/c π^-p interactions, the various two-pion and four-pion decay channels available to the g^- meson have been investigated. Our results indicate that the dominant 4π decay modes involve intermediate ρ and ω production without significant A₂ formation.

Results of a high-statistics study of elastic scattering and meson resonances produced by π^-p interactions at 8 GeV/c are presented. Large statistics and small systematic errors permit examination of the complete kinematic region. Total differential cross sections are given for ρ^0,-, f⁰, g^0,-, Δ^±, Δ⁰, and N^* resonances. Spin-density matrix elements and Legendre-polynomial moments are given for ρ, f, and Δ resonances. The results for ρ⁰ and f⁰ resonances are compared with the predictions of a Regge-pole-exchange model. Properties of the above resonances are compared and discussed. In particular, we present evidence that the ρ⁰ and f⁰ production mechanisms are similar. The similarity of the g⁰ t distribution to that of the ρ⁰ and f⁰ suggests a common production mechanism for all three resonances.

Results from a high-statistics experiment involving an exposure of the SLAC 82-in. hydrogen bubble chamber to a beam of 8-GeV/c π^- yielding a final state of π^-π⁺π^-p are presented. Copious production of ρ, Δ⁺⁺, and f is found. Considerable quasi-two-body production in which one particle decays to one of the above resonances is also observed. Some double-resonance production involving baryon and meson resonances is also seen. The production properties of ρ, Δ⁺⁺, and f mesons are well described by a double-Regge model.

The Fermilab hybrid 30-in. bubble-chamber spectrometer was exposed to a tagged 147-GeV/c positive beam containing π⁺, K⁺, and p. A sample of 3003 K⁺p, 19 410 pp, and 20 745 π⁺p interactions is used to derive σ_n, 〈n〉, f₂^cc, and 〈n_c〉 / D for each beam particle. These values are compared to values obtained at other, mostly lower, beam momenta. The overall dependence of 〈n〉 on E_a, the available center-of-mass energy, for these three reactions as well as π^-p and pp interactions has been determined.

We have studied the inclusive production of K^*±(890) and Y^*±(1385) in pp, π⁺p, and K⁺p interactions at 147 GeV/c. The experiment used the Fermilab 30-inch hydrogen bubble chamber with the hybrid spectrometer system. Results are based on a sample of 1916 observed K_S and 932 observed A. Inclusive cross sections are given for K^*± and Y^*± production from the three beams, and comparisons are made with experiments at other energies. Feynman-x and transverse-momentum-squared distributions are also calculated. The results suggest that the K^*- is entirely produced in the central region, while the K^*+ includes a component from beam fragmentation. Comparisons are made with the additive quark model.

We have studied inclusive ρ⁰ and Δ⁺⁺ production in π⁺p and π^-p interactions at 15 GeV/c in a region where pion exchange has been found to dominate the resonance production. By using ρ⁰ production, the off-mass-shell interactions of virtual pions with the target protons have been studied and compared with the same on-shell reactions at comparable energy. No significant differences between on-shell and off-shell reactions have been found in topological-cross-section ratios, inclusive longitudinal- or transverse-momentum distributions, or elastic dσ / dt distributions. The effect of the negative mass squared of the virtual pions has also been studied. Inclusive Δ⁺⁺ production has been found to be dominated by pion exchange for |t|≲0.4 (GeV/c)². We have studied the interactions of these off-shell pions with the beam pions as a function of energy. The ratio σ_el / σ_T and the average charged-particle multiplicities 〈n_X〉 have been examined and compared with those for various hadron-proton reactions. The values of 〈n_X〉 have also been studied in terms of a simple model and found to give results consistent with studies at higher energies. We also present longitudinal- and transverse-momentum distributions for produced pions, as well as dσ / dt distributions for ππ elastic scattering.

Diffraction dissociation of both the beam and target particles has been observed in 150-GeV/c π^-p interactions in the Fermilab 30-in.-bubble-chamber-proportional-wire-chamber hybrid spectrometer. The dissociations are observed as recoil systems opposite leading particles, the signals of which are separated from background where appropriate by a variant of the Van Hove sector cut, thus allowing the high-mass portion of the spectrum to be observed. Pion dissociation has a cross section of 1758±105 μb, divided among two-, four-, and six-prong events; some ρ⁰ production is seen and comes primarily from the π^-→2π^-π⁺ channel. The proton dissociation cross section is 1726±100 μb, again divided among two-, four-, and six-prong events. The final state contains a neutron more frequently than a proton in the two-and six-prong events, a proton more frequently in the four-prong events. Production of Δ⁺⁺ is observed in the p→pπ⁺π^- dissociations.

We have studied inclusive Δ⁺⁺ production at 147 GeV/c in pp, K⁺p, π⁺p, and π^-p interactions. All four reactions were detected with the same apparatus and analyzed in the same way. The energy dependence of the Δ⁺⁺ cross section was found to be Ap^-1+B for pp, K⁺p, and π⁺p interactions and constant for π^-p interactions. The shape of the inclusive Δ⁺⁺ distributions does not depend on the beam, while the magnitudes are proportional to the total cross sections. We have obtained the effective trajectory at the p-Δ⁺⁺ vertex from a triple-Regge analysis and found that all results are consistent with predictions of a triple-Regge diagram where a Pomeron is exchanged at the beam vertex and a π at the target vertex.

The production of K_S, Λ, Λ̅ , and γ in π^-p collisions at 147 GeV/c is analyzed. Cross sections, rapidity, Feynman-x, and p_T² distributions are presented and compared to charged-particle production. The energy dependence of multiplicities in π^-p and pp collisions is shown. A new scaling form for the correlation of neutral- and charged-particle multiplicities is presented for compilations of πp and pp data.

The experimentally determined average charged-particle multiplicities, 〈n_X〉, of the systems, X, produced in the following reactions for 147 GeV/c incident pion momentum are presented as functions of the square of the invariant mass of X, M_X², and of |t|:π^-p→π_fast^-X, π^-p→pX, π^-p→Δ⁺⁺X, π^-p→(π^-π⁺)_ρ⁰X, and π^-p→Λ⁰X. Details of the analysis are discussed. These data can be fit by the expression 〈n_X〉=A+B ln M_X²+C|t| and the coefficients obtained for B are equal within their uncertainties. C is significantly different from zero only for π^-p→π_fast^-X. These results and 〈n_X〉 data from other inclusive and total-inelastic-reaction studies are discussed in terms of a simple model which assumes contributions to 〈n_X〉 from the target-fragmentation, the central, and the beam-fragmentation regions in the case of total-inelastic reactions. For inclusive reactions, either the beam or target fragmentation is replaced by an exchange-particle-fragmentation contribution. The s, t, and M_X² dependence of the parameters of the model are deduced from triple-Regge considerations. The data are found to be consistent with the model and values are presented for the parameters.

The inclusive production of the Δ⁺⁺(1232) resonance in π^-p collisions at 147 GeV/c has been studied. The Δ⁺⁺ is found to be produced in comparable amounts in four-, six-, eight-, and ten-prong events. The Feynman-x, t^′, P_T², and the decay angular distributions of the Δ⁺⁺ are found to be consistent with the predictions of a one-pion-exchange model with absorption. Essentially all of the Δ⁺⁺ are found to be associated with a Δ⁺⁺π^- low-mass enhancement. The Δ⁺⁺ cross section is approximately constant from 11 to 205 GeV/c, which could indicate that the Δ⁺⁺ is a decay product of a target-fragmentation object. While the one-pion-exchange character of the Δ⁺⁺ production and the target-fragmentation character of the Δ⁺⁺π^- low-mass enhancement can both be described in terms of a Deck-type diagram, a Monte Carlo study indicates that any mechanism that produces particles with limited transverse momentum will yield a Δ⁺⁺π^- low-mass enhancement.

We examine the polarization properties exhibited by ρ⁰'s and ω⁰'s in the reactions π^-+p→ρ⁰+X⁰ and π^-+p→ω⁰+charged particles at 15 GeV/c. ρ⁰ production is analyzed in the framework of the triple Regge model. The trajectory coupled to the π^- ρ⁰ is α(t)=(-0.12±0.07)+(0.78±0.21)t in good agreement with the π trajectory. The properties of the system recoiling against the ρ⁰ (off-shell ``π^-''p reaction) are very similar to those of the final states of on-shell π^-p reactions at the same center-of-mass energy.

We present in this paper a study of the Δ⁺⁺(1232) inclusive production for momentum transfer squared to the target proton, |t|<1 (GeV/c)². We have investigated the production mechanism of the Δ⁺⁺ by measuring its density matrix elements as a function of t and of the missing mass squared, M_X², and by carrying out a triple-Regge analysis. For |t|<0.4 (GeV/c)², the Δ⁺⁺ production mechanism is consistent with one-pion exchange. We have also studied the average charged multiplicity recoiling from the Δ⁺⁺ as a function of M_X², for |t|<0.4 (GeV/c)². The study yields information about the π^-π^- average charged multiplicity.

A study of the inclusive production of K_S⁰, Λ, and Λ̅ in π^-p interactions at 15 GeV / c is presented. Inclusive cross sections for single neutral strange particles and neutral-strange-particle pairs are given. Longitudinal- and transverse-momentum distributions of the produced particles are presented. The average charged multiplicities of the systems recoiling against the Λ and the K_S⁰ are compared and the results analyzed in the framework of a simple model. The Λ polarization is found to be in good agreement with Λ production from other strangeness-nonannihilating processes. Production of Λ's in the target fragmentation region is studied in the framework of the triple-Regge-pole-exchange model. The cross section for inclusive K^*+(890) production has been measured as 195 ± 35 μb, and the Σ⁺(1385) inclusive cross section has been found to be 174 ± 25 μb. The K^*+(890) and Σ⁺(1385) differential cross sections as functions of rapidity and transverse momentum are presented and discussed.

The reactions γp→p2π⁺2π^-π⁰ and γp→n3π⁺2π^- have been studied in three exposures of the SLAC 40-inch hydrogen bubble chamber to a positron-annihilation radiation of energies 4.3, 5.25, and 7.5 GeV. Cross sections for Δ⁺⁺(1236), ω, η, and ρ production are given. The associated production γp→Δ⁺⁺ω⁰π^- is discussed in terms of a double-Regge exchange model and compared with the reaction γp→Δ⁺⁺ρπ^-.

The reaction πp→pπ⁺π⁺π^-π^- has been studied in the energy interval 1.5 - 12.0 GeV, using the SLAC 40-inch liquid hydrogen bubble chamber exposed to the SLAC annihilation beam. Total and differential cross sections are presented for the reactions γp→Δ⁺⁺π⁺π^-π^-, γp→pρ⁰π⁺π^- and γp→Δ⁺⁺ρ⁰π^-. The last reaction is analyzed in terms of a double-Regge-exchange model.

The reaction γd→π^-+anything at 7.5 GeV with a linearly polarized photon beam has been studied. The γn average charge multiplicity was found to be a unit charge less than the γp average charge multiplicity. We have extracted information on the inclusive π^- production in γn reactions using the γp inclusive data. The ratio of π⁺ to π^- inclusive production in the target fragmentation region was found to be independent of the beam. Two-particle correlations in both x and y variables are presented.

We see a significant peak (M=1.446±0.011 GeV, Γ=198±40 MeV), consistent with a I=1 / 2, J=1 / 2 state, in the pπ^- mass distribution of the reaction pd→p_sppπ^- at 7.0 GeV/c. We interpret it as the N^*(1470) produced in the reaction pn→pN^*0(1470) [N^*0(1470)→pπ^-] in deuterium. The production of the N^*(1470) is strongly peripheral and favors I=0 exchange. A discussion of this peak in terms of a double-Regge-pole exchange mechanism is presented.