Search Results (25 total)

We show that Σ⁺ hyperons produced by 800 GeV/c protons on targets of Be and Cu have significant polarizations (15–20%). These polarizations persist at values of p_t≈2  GeV/c and a wide range of x_F. The polarizations from the Cu target are consistently less than from Be. The average ratio of the Σ⁺ polarization from Cu to that from Be is 0.68±0.08.

We report the first observation of a charm-strange meson D_sJ⁺(2632) at a mass of 2632.5±1.7  MeV/c² in data from SELEX, the charm hadro-production experiment E781 at Fermilab. This state is seen in two decay modes, D_s⁺η and D⁰K⁺. In the D_s⁺η decay mode we observe a peak with 101 events over a combinatoric background of 54.9 events at a mass of 2635.4±3.3  MeV/c². There is a corresponding peak of 21 events over a background of 6.9 at 2631.5±2.0  MeV/c² in the decay mode D⁰K⁺. The decay width of this state is <17  MeV/c² at 90% confidence level. The relative branching ratio Γ(D⁰K⁺)/Γ(D_s⁺η) is 0.14±0.06. The mechanism that keeps this state narrow is unclear. Its decay pattern is also unusual, being dominated by the D_s⁺η decay mode.

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.

Pion virtual compton scattering (VCS) via the reaction π^-e→π^-eγ was observed in the Fermilab E781 SELEX experiment. SELEX used a 600 GeV/c π^- beam incident on target atomic electrons, detecting the incident π^- and the final state π^-, electron and γ. Theoretical predictions based on chiral perturbation theory are incorporated into a Monte Carlo simulation of the experiment and are compared to the data. The number of reconstructed events (=9) and their distribution with respect to the kinematic variables (for the kinematic region studied) are in reasonable accord with the predictions. The corresponding π^- VCS experimental cross section is σ=38.8±13 nb, in agreement with the theoretical expectation of σ=34.7 nb.

We observe a signal for the doubly charmed baryon Ξ_cc⁺ in the charged decay mode Ξ_cc⁺→Λ_c⁺K^-π⁺ in data from SELEX, the charm hadroproduction experiment at Fermilab. We observe an excess of 15.9 events over an expected background of 6.1±0.5 events, a statistical significance of 6.3σ. The observed mass of this state is 3519±1  MeV/c². The Gaussian mass width of this state is 3  MeV/c², consistent with resolution; its lifetime is less than 33 fs at 90% confidence.

We report new precision measurements of the lifetimes of the Λ_c⁺ and D⁰ from SELEX, the charm hadroproduction experiment at Fermilab. Based upon 1630 Λ_c⁺ and 10 210 D⁰ decays we observe lifetimes of τ[Λ_c⁺]  =  198.1±7.0±5.6 fs and τ[D⁰]  =  407.9±6.0±4.3 fs.

We report the first observation of the Cabibbo-suppressed charm baryon decay Ξ_c⁺→pK^-π⁺. We observe 150±22±5 events for the signal. The data were accumulated using the SELEX spectrometer during the 1996–1997 fixed target run at Fermilab, chiefly from a 600 GeV/c Σ^- beam. The branching fractions of the decay relative to the Cabibbo-favored Ξ_c⁺→Σ⁺K^-π⁺ and Ξ_c⁺→Ξ^-π⁺π⁺ are measured to be B(Ξ_c⁺→pK^-π⁺)/B(Ξ_c⁺→Σ⁺K^-π⁺)  =  0.22±0.06±0.03 and B(Ξ_c⁺→pK^-π⁺)/B(Ξ_c⁺→Ξ^-π⁺π⁺)  =  0.20±0.04±0.02, respectively.

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)].

In Fermilab experiment E683 we have used a large solid angle calorimeter to study the production of hadronic events with large transverse energy in γp and πp collisions at center-of-mass energies from 20 to 25 GeV. We observe a sudden shift in γp event topology with increasing transverse energy, indicative of the emergence of jet dominance. This is the first observation of such a shift in event topology in fixed-target interactions. πp interactions in the same kinematic region and under identical triggering conditions exhibit only a slight shift in event topology.

Surprisingly large polarizations in hyperon production by unpolarized protons have been known for a long time. The spin dynamics of the production process can be further investigated with polarized beams. Recently, a negative asymmetry A_N was found in inclusive Λ⁰ production with a 200 GeV/c transversely polarized proton beam. The depolarization D_NN in p↑+p→Λ⁰+X has been measured with the same beam over a wide x_F range and at moderate p_T. D_NN reaches positive values of about 30% at high x_F and p_T∼1.0 GeV/c. This result shows a sizable spin transfer from the incident polarized proton to the outgoing Λ⁰.

The highest-energy measurement of Δσ_L(pp) and the first ever measurement of Δσ_L(p¯p), the differences between proton-proton and antiproton-proton total cross sections for pure longitudinal spin states, are described. Data were taken using 200-GeV/c polarized beams incident on a polarized-proton target. The results are measured to be Δσ_L(pp)=-42 ± 48(stat)± 53(syst) μb and Δσ_L(p¯p)=-256 ± 124(stat)± 109(syst) μb. Many tests of systematic effects were investigated and are described, and a comparison to theoretical predictions is also given. Measurements of parity nonconservation at 200 GeV/c in proton scattering and the first ever of antiproton scattering have also been derived from these data. The values are consistent with zero at the 10^-5 level.

The analyzing power A_N in inclusive π^- and π⁺ production has been measured with a 200 GeV/c transversely polarized antiproton beam over a wide x_F range (0.2≤x_F≤0.9) and at moderate p_T (0.2≤p_T≤1.5 GeV/c). The asymmetry A_N increases with increasing x_F from zero to large positive values for π^-'s, and decreases from zero to large negative values for π⁺'s. A threshold for the onset of the asymmetry is observed about p_T∼0.5 GeV/c, below which A_N is essentially zero and above which A_N increases (decreases) with p_T for π^-'s ( π⁺'s) in the covered p_T range.

The π⁰ inclusive and semi-inclusive, single-spin asymmetries have been measured using transversely polarized, 200-GeV/c proton and antiproton beams colliding with an unpolarized hydrogen target. The measured asymmetries are consistent with zero within the experimental uncertainties for the kinematic region -0.15<x_F<+0.15 and 1<p_T<4.5 GeV/c. Improvements in the data analysis showed that our earlier large asymmetries at p_T≳3 GeV/c were not correct. These data indicate that PQCD expectations seem confirmed and the higher-twist contribution to the single-spin asymmetry in π⁰ production at x_F=0 is not large. Additional evidence for such a conclusion comes from the measurement of a semi-inclusive π⁰ asymmetry, where associated charged particles are detected opposite to the π⁰ azimuthal direction. This experiment also provides high-statistics data on the inclusive π⁰ cross sections for pp and p¯p collisions at √s≊19.4 GeV. © 1996 The American Physical Society.

The considerable polarization of hyperons produced at high x_F has been known for a long time and has been interpreted with various theoretical models in terms of the constituents' spin. Recently, the analyzing power in inclusive Λ⁰ hyperon production has also been measured using the 200 GeV/c Fermilab polarized proton beam. The covered kinematic range is 0.2≤x_F≤1.0 and 0.1≤p_T≤1.5 GeV/c. The data indicate a negative asymmetry at large x_F and moderate p_T. These results can further test the current ideas on the underlying mechanisms for hyperon polarization.

We present a measurement of the A dependence of k_Tφ, the out-of-plane component of the dijet transverse momentum, in dijet events produced with a real photon beam. We also present the same measurement for dijets produced from pion-nucleus collisions in our detector. Both data sets are taken at a mean √s of 21 GeV in the p_T range 3–7 GeV/c. A clear A dependence of comparable magnitude is seen in both processes. The energy dependence of the nuclear behavior is also extracted.

Interactions of high energy photons on a hyrogen target have been studied using a large acceptance segmented calorimeter. The event topology clearly shows the production of dijet final states as predicted by perturbative QCD. The energy flow in the photon (forward) direction is compared both to Monte Carlo expectations and to that produced in πp interactions.

The analyzing power A_N of proton-proton elastic scattering in the Coulomb-nuclear interference region has been measured using the 200-GeV/c Fermilab polarized proton beam. A theoretically predicted interference between the hadronic non-spin-flip amplitude and the electromagnetic spin-flip amplitude is shown for the first time to be present at high energies in the region of 1.5 × 10^-3 to 5.0 × 10^-2 (GeV/c)² four-momentum transfer squared, and our results are analyzed in connection with theoretical calculations. In addition, the role of possible contributions of the hadronic spin-flip amplitude is discussed.

Polarized, stored beams are becoming a more and more important tool in nuclear and high-energy physics. In order to measure the beam polarization in a storage ring the polarization vector of the stored beam has to aim, revolution for revolution, over a period of seconds to minutes, into the same, so-called ‘‘stable’’ direction. In this paper measurements at the Indiana University Cooler Ring are described in which for the first time in a storage ring, oscillations around this stable direction have been measured. The existence and the dynamics of such oscillations are, for instance, important for a new proposed technique for polarizing stored hadron beams.

The polarization parameter P_n000, the two-spin parameters D_n0n0, K_n00n, D_s^′0s0, D_s^′0k0 and the three-spin parameters M_s^′0sn and M_s^′0kn have been measured for pp elastic scattering angles between 60° and 88° center of mass at 241 and 314 MeV incident kinetic energies, and between 38° c.m. and 98° c.m. at 341, 366, and 398 MeV. At 473 MeV, only P_n000 and D_s^′0k0 were measured between 34° c.m. and 62° c.m. The experiment was performed at SIN using a polarized proton beam and a polarized butanol target. The polarization of the scattered proton was analyzed in a carbon polarimeter. The influence of these high-precision data on the Saclay-Geneva phase-shift analysis is discussed.

A direct experimental reconstruction of the five complex pp elastic-scattering amplitudes has been performed at 447, 497, 517, 539, and 579 MeV. The reconstruction is done over the c.m. angles from 38° to 90° and is based on either 11 or 15 spin observables depending on the angular range. The reconstructed amplitudes are presented and compared to phase-shift analysis. A smooth energy behavior is observed for the amplitudes.

The polarization parameter P_n000, the two-spin parameters D_n0n0, K_n00n, D_s0s0, D_s0k0, and the three-spin parameters M_s0sn and M_s0kn have been measured for pp elastic scattering between 34° and 118° center-of-mass scattering angle at six different incident kinetic energies 447, 473, 497, 517, 539, and 560 MeV. The experiment was performed at SIN using a polarized proton beam, a polarized butanol target, and a polarimeter for the measurement of the polarization of the scattered proton.

We have measured the spin-correlation parameters A_00kk, A_00ks, and A_00ss in p-p scattering between 400 and 600 MeV using a longitudinally polarized beam and a butanol target polarized in the horizontal plane. Owing to the restrictive geometrical acceptance of the target, the polarization axis of the target was oriented at an angle α with respect to beam direction. The parameters A_00kk and A_00ks were therefore measured as a linear combination at 577, 536, 514, 494, and 445 MeV. These experiments were extended to the measurement of A_00ks and A_00ss by using a transversely polarized beam. We present the results, which are compared with phase-shift predictions.

The polarization parameter P_n000, the two-spin parameters D_n0n0, K_n00n, D_s0s0, and D_s0k0, and the three-spin parameters M_s0sn and M_s0kn have been measured for pp elastic scattering at 579 MeV between 34° and 118° center-of-mass scattering angle. The experiment was performed at SIN using a polarized proton beam, a polarized butanol target, and a polarimeter for the measurement of the polarization of the scattered proton. These data form the basis for a complete experimental determination of the scattering amplitudes.

A model-independent upper limit on the time-reversal-invariance (TRI) violating amplitude in elastic pp scattering based on a direct experimental reconstruction of the scattering matrix is presented. This analysis is made possible by a set of sixteen polarization parameters measured at the Swiss Institute for Nuclear Research for 579-MeV elastic pp scattering at six center-of-mass angles between 66° and 86°. Less than 1% is found for the fraction of TRI-violating cross section.

We have made, for the first time, a direct reconstruction of the pp elastic-scattering matrix at 579 MeV from a series of experiments performed at the Schweizerisches Institut für Nuklearforschung polarized-beam line. Fifteen observables consisting of the polarization, two-spin correlation and transfer parameters, and three-spin parameters were measured at seven angles between 66° and 90° (c. m.). The experimental results and reconstructed amplitudes are presented and compared to phase shift analysis.