Search Results (80 total)

We report a measurement of the angular distributions of Drell-Yan dimuons produced using an 800  GeV/c proton beam on a hydrogen target. The polar and azimuthal angular distribution parameters have been extracted over the kinematic range 4.5<m_μμ<15  GeV/c² (excluding the Υ resonance region), 0<p_T<4  GeV/c, and 0<x_F<0.8. The p+p angular distributions are similar to those of p+d, and both data sets are compared with models which attribute the cos⁡2ϕ distribution either to the presence of the transverse-momentum-dependent Boer-Mulders structure function h₁^⊥ or to QCD effects. The data indicate the need to include QCD effects before reliable information on the Boer-Mulders function can be extracted. The validity of the Lam-Tung relation in p+p Drell-Yan data is also tested.

We report a high statistics measurement of Υ production with an 800  GeV/c proton beam on hydrogen and deuterium targets. The dominance of the gluon-gluon fusion process for Υ production at this energy implies that the cross section ratio, σ(p+d→Υ)/2σ(p+p→Υ), is sensitive to the gluon content in the neutron relative to that in the proton. Over the kinematic region 0<x_F<0.6, this ratio is found to be consistent with unity, in striking contrast to the behavior of the Drell-Yan cross section ratio σ(p+d)_DY/2σ(p+p)_DY. This result shows that the gluon distributions in the proton and neutron are very similar. The Υ production cross sections are also compared with the p+d and p+Cu cross sections from earlier measurements.

We report a measurement of the angular distributions of Drell-Yan dimuons produced using an 800  GeV/c proton beam on a deuterium target. The muon angular distributions in the dilepton rest frame have been measured over the kinematic range 4.5<m_μμ<15  GeV/c², 0<p_T<4  GeV/c, and 0<x_F<0.8. No significant cos⁡2ϕ dependence is found in these proton-induced Drell-Yan data, in contrast with the situation for pion-induced Drell-Yan data. The data are compared with expectations from models which attribute the cos⁡2ϕ distribution to a QCD vacuum effect or to the presence of the transverse-momentum-dependent Boer-Mulders structure function h₁^⊥. Constraints on the magnitude of the sea-quark h₁^⊥ structure functions are obtained.

The asymmetry in the p̅ angular distribution in the sequential decay Ω̅ ⁺→Λ̅ K⁺→p̅ π⁺K⁺ has been measured to be α̅ _Ωα̅ _Λ=[+1.16±0.18(stat)±0.17(syst)]×10^-2 using 1.89×10⁶ unpolarized Ω̅ ⁺ decays recorded by the HyperCP (E871) experiment at Fermilab. Using the known value of α_Λ, and assuming that α̅ _Λ=-α_Λ, α̅ _Ω=[-1.81±0.28(stat)±0.26(syst)]×10^-2. A comparison between this measurement of α̅ _Ωα̅ _Λ and recent measurements of α_Ωα_Λ made by HyperCP shows no evidence of a violation of CP symmetry.

A sensitive search for the lepton-number-violating decay Ξ^-→pμ^-μ^- has been performed using a sample of ∼10⁹  Ξ^- hyperons produced in 800  GeV/c p-Cu collisions. We obtain B(Ξ^-→pμ^-μ^-)<4.0×10^-8 at 90% confidence, improving on the best previous limit by 4 orders of magnitude.

A sensitive search for the rare decays Ω^-→Λπ^- and Ξ⁰→pπ^- has been performed using data from the 1997 run of the HyperCP (Fermilab E871) experiment. Limits on other such processes do not exclude the possibility of observable rates for |ΔS|=2 nonleptonic hyperon decays, provided the decays occur through parity-odd operators. We obtain the branching-fraction limits B(Ω^-→Λπ^-)<2.9×10^-6 and B(Ξ⁰→pπ^-)<8.2×10^-6, both at 90% confidence level.

We have measured the α parameter of the Ω^-→ΛK^- decay using data collected with the HyperCP spectrometer during the 1997 fixed-target run at Fermilab. Analyzing a sample of 0.96×10⁶ Ω^-→ΛK^-, Λ→pπ^- decays, we obtain α_Ωα_Λ=[1.33±0.33(stat)±0.52(syst)]×10^-2. With the accepted value of α_Λ, α_Ω is found to be [2.07±0.51(stat)±0.81(syst)]×10^-2.

We report the first evidence for the decay Σ⁺→pμ⁺μ^- from data taken by the HyperCP (E871) experiment at Fermilab. Based on three observed events, the branching ratio is B(Σ⁺→pμ⁺μ^-)=[8.6_-5.4^+6.6(stat)±5.5(syst)]×10^-8. The narrow range of dimuon masses may indicate that the decay proceeds via a neutral intermediate state, Σ⁺→pP⁰,P⁰→μ⁺μ^- with a P⁰ mass of 214.3±0.5  MeV/c² and branching ratio B(Σ⁺→pP⁰,P⁰→μ⁺μ^-)=[3.1_-1.9^+2.4(stat)±1.5(syst)]×10^-8.

We have compared the p and p̅ angular distributions in 117×10⁶ Ξ^-→Λπ^-→pπ^-π^- and 41×10⁶ Ξ̅ ⁺→Λ̅ π⁺→p̅ π⁺π⁺ decays using a subset of the data from the HyperCP experiment (E871) at Fermilab. We find no evidence of CP violation, with the direct-CP-violating parameter A_ΞΛ≡(α_Ξα_Λ-α̅ _Ξα̅ _Λ)/(α_Ξα_Λ+α̅ _Ξα̅ _Λ)=[0.0±5.1(stat)±4.4(syst)]×10^-4.

We have searched for θ⁺(1.54)→K⁰p decays using data from the 1999 run of the HyperCP experiment at Fermilab. We see no evidence for a narrow peak in the K_S⁰p mass distribution near 1.54  GeV/c among 106 000 K_S⁰p candidates, and obtain an upper limit for the fraction of θ⁺(1.54) to K_S⁰p candidates of <0.3% at 90% confidence.

Based on a sample of 144×10⁶ polarized Ξ^-→Λπ^-,Λ→pπ^- decays collected by the HyperCP experiment (E871) at Fermilab, we report a new measurement of the Ξ^- decay-parameter angle φ_Ξ=(-2.39±0.64±0.64)° from which we deduce the decay parameters β_Ξ=-0.037±0.011±0.010 and γ_Ξ=0.888±0.0004±0.006. Assuming that the CP-violating phase difference between s and p waves is negligible, the strong phase-shift difference, δ_p-δ_s, for Λπ scattering is determined to be (4.6±1.4±1.2)°.

We present measurements of the polarization of the J/ψ produced in 800-GeV proton interactions with a copper target. Polarization of the J/ψ is sensitive to the cc̅ production and hadronization processes. A longitudinal polarization is observed at large x_F, while at small x_F the state is produced essentially unpolarized or slightly transversely polarized. No significant variation of the polarization is observed versus p_T.

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.

We have used modern supercomputer facilities to carry out extensive numerical simulations of statistical properties of one-dimensional (1D) and 2D arrays of single-electron islands with random background charges, in the limit of small island self-capacitance. In particular, the spectrum of single-electron addition energies shows a clear Coulomb gap that, in 2D arrays, obeys the Efros-Shklovskii theory modified for the specific electron-electron interaction law. The Coulomb blockade threshold voltage statistics for 1D arrays is very broad, with the rms width δV_t growing as 〈V_t〉∝N^1/2 with the array size N. On the contrary, in square 2D arrays of large size the distribution around 〈V_t〉∝N becomes relatively narrow (δV_t/〈V_t〉∝1/N), and the dc I-V curves are virtually universal. At low voltages, the slope G₀(T) of I-V curves obeys the Arrhenius law. The corresponding activation energy U₀ grows only slowly with N and is considerably lower than the formally calculated “lowest pass” energy E_max of the potential profile, thus indicating the profile “softness.”

Based on 1.35×10⁶ polarized Ξ^- events, we measure the parameter ϕ_Ξ to be -1.61°±2.66°±0.37° for the Ξ^-→Λπ^- decay. New results for the parameters β_Ξ and γ_Ξ are also presented. Assuming that the CP-violating phase difference is negligible, we deduce the strong phase difference between the P-wave and S-wave amplitudes of the Λπ final state to be 3.17°±5.28°±0.73°, reducing the uncertainty in estimating the level of CP violation in Ξ-hyperon decay.

We have shown that a special distribution of background charges in islands of single-electron-tunneling arrays can completely suppress its Coulomb blockade and at the same time reduce substantially its shot noise at low applied voltages. In particular the Fano factor F can approach the minimum value F_min=1/N≪1 (where N is the array length). Thus both conditions of subelectron transport formulated earlier by Matsuoka and Likharev [Phys. Rev. B 57, 15 613 (1998)] can be satisfied. At larger voltages, field-induced generation of holes becomes possible, and the Fano factor grows, before dropping to F_min again at even higher voltages. We discuss the physics of the resulting shot-noise peak and conclude that it is very similar to that of the critical opalescence.

Using data collected with the HyperCP (E871) spectrometer during the 1997 fixed-target run at Fermilab, we report the first observation of the decay K^-→π^-μ⁺μ^- and new measurements of the branching ratios for K^±→π^±μ⁺μ^-. By combining the branching ratios for the decays K⁺→π⁺μ⁺μ^- and K^-→π^-μ⁺μ^-, we measure Γ(K^±→π^±μ⁺μ^-)/Γ(K^±→all)  =  (9.8±1.0±0.5)×10^-8. The CP asymmetry between the rates of the two decay modes is [Γ(K⁺→π⁺μ⁺μ^-)-Γ(K^-→π^-μ⁺μ^-)]/[Γ(K⁺→π⁺μ⁺μ^-)+Γ(K^-→π^-μ⁺μ^-)]  =  -0.02±0.11±0.04.

We present a new analysis of the E772 and E866 experiments on the nuclear dependence of Drell-Yan (DY) lepton pair production resulting from the bombardment of ²H, Be, C, Ca, Fe, and W targets by 800 GeV/c protons at Fermilab. We employ a light-cone formulation of the DY reaction in the rest frame of the nucleus, where the dimuons detected at small values of Bjorken x₂≪1 may be considered to originate from the decay of a heavy photon radiated from an incident quark in a bremsstrahlung process. We infer the energy loss of the quark by examining the suppression of the nuclear-dependent DY ratios seen as a function of projectile momentum fraction x₁ and dimuon mass M. Shadowing, which also leads to nuclear suppression of dimuons, is calculated within the same approach employing the results of phenomenological fits to deep inelastic scattering data from HERA. The analysis yields -dE/dz=2.73±0.37±0.5 GeV/fm for the rate of quark energy loss per unit path length, a value consistent with theoretical expectations including the effects of the inelastic interaction of the incident proton at the surface of the nucleus. This is the first observation of a nonzero energy loss effect in such experiments.

Measurements of the ratio of Drell-Yan yields from an 800 GeV/c proton beam incident on liquid hydrogen and deuterium targets are reported. Approximately 360 000 Drell-Yan muon pairs remained after all cuts on the data. From these data, the ratio of down antiquark (d̅ ) to up (ū) antiquark distributions in the proton sea is determined over a wide range in Bjorken-x. These results confirm previous measurements by E866 and extend them to lower x. From these data, (d̅ -ū) and ∫(d̅ -ū)dx are evaluated for 0.015<x<0.35. These results are compared with parametrizations of various parton distribution functions, models and experimental results from NA51, NMC and HERMES.

Numerical modeling of correlated single-electron tunneling in uniform two-dimensional arrays of small conducting islands separated by tunnel junctions shows the possibility of soliton-antisoliton avalanches. Though the time duration of any avalanche and the total charge, ΔQ=ne, transferred across the array during the avalanche are always finite in arrays with length N larger than certain critical value N_c and large width M, the avalanche magnitude n may be exponentially large, resulting in particular in a giant increase of shot noise. Thermal fluctuations gradually suppress the avalanche effect. Background charge disorder may lead (in larger arrays) to a gradual change of avalanche character and to a crossover from the avalanche-induced shot noise to 1/f-type noise.

We report an analysis of the nuclear dependence of the yield of Drell-Yan dimuons from the 800 GeV/c proton bombardment of ²H, C, Ca, Fe, and W targets. Employing a new formulation of the Drell-Yan process in the rest frame of the nucleus, this analysis examines the effect of initial-state energy loss and shadowing on the nuclear-dependence ratios versus the incident proton's momentum fraction and dimuon effective mass. The resulting energy loss per unit path length is -dE/dz  =  2.32±0.52±0.5 GeV/fm. This is the first observation of a nonzero energy loss of partons traveling in a nuclear environment.

In the past few years, the concept of a high intensity muon storage ring has been pursued as an option for the next generation neutrino source. To produce the high intensity muon beam needed for the successful operation of a neutrino source, on the order of 10²⁰ muon decays per year, the phase space occupied by the muon beam must be significantly reduced before the beam is accelerated. The initial transverse emittance of the muon beam before acceleration is assumed to be 9π mm rad. Because of the time limitation imposed by the muon lifetime, the technique employed to accomplish the desired emittance reduction is ionization cooling. In this paper we present two ionization cooling lattice designs, which use solenoidal focusing elements and liquid hydrogen absorbers to reduce the muon beam phase space. We discuss the design concepts and engineering constraints for these lattices and present simulation results obtained using a detailed tracing code with a complete model of muon-matter interactions. The reduction in transverse emittance is approximately a factor of 5. This result is within a factor of 2 of the total cooling requirements for a successful neutrino factory design and within a factor of 1.4 of the requirements for the main cooling section specified in the conceptual design of this machine.

We present a measurement of the polarization observed for bottomonium states produced in p-Cu collisions at sqrt[s]  =  38.8  GeV. The angular distribution of the decay dimuons of the ϒ(1S) state shows no polarization at small values of the fractional longitudinal momentum x_F and transverse momentum p_T but significant positive transverse production polarization for either p_T>1.8  GeV/c or for x_F>0.35. The ϒ(2S+3S) (unresolved) states show a large transverse production polarization at all values of x_F and p_T measured. These observations challenge NRQCD calculations of the polarization expected in the hadronic production of bottomonium states.

Measurements of the suppression of the yield per nucleon of J/ψ and ψ^′ production for 800 GeV/ c protons incident on heavy nuclear targets, relative to light nuclear targets, have been made with very broad coverage in x_F and p_T. The observed suppression is smallest at x_F values of 0.25 and below, and increases at larger values of x_F. It is also strongest at small p_T. Substantial differences between ψ^′ and J/ψ production are observed for the first time in p-A collisions. The suppression for ψ^′ production is stronger than that for J/ψ for x_F near zero, but becomes comparable to that for J/ψ for x_F>0.6.

We present the results of a search for the three neutral charm decays D⁰→μ^±e^∓, D⁰→μ⁺μ^-, and D⁰→e⁺e^-. This study was based on data collected in Experiment 789 at the Fermi National Accelerator Laboratory using 800 GeV/c proton-Au and proton-Be interactions. No evidence is found for any of the decays. Upper limits on the branching ratios, at the 90% confidence level, of 1.56×10^-5 for D⁰→μ⁺μ^-, 8.19×10^-6 for D⁰→e⁺e^- and 1.72×10^-5 for D⁰→μ^±e^∓ are obtained.