The STAR Collaboration reports the first observation of exclusive rho(0) photoproduction, AuAu-->AuAurho(0), and rho(0) production accompanied by mutual nuclear Coulomb excitation, ...AuAu-->Au*Au*rho(0), in ultraperipheral heavy-ion collisions. The rho(0) have low transverse momenta, consistent with coherent coupling to both nuclei. The cross sections at sqrts(NN)=130 GeV agree with theoretical predictions treating rho(0) production and Coulomb excitation as independent processes.
The design of a time projection chamber (TPC) detector with complete pad coverage is presented. The TPC allows the measurements of high multiplicity ( approximately 200 tracks) relativistic ...nucleus-nucleus collisions initiated with the heaviest, most energetic projectiles available at the LBL (Lawrence Berkeley Laboratory) BEVALAC accelerator facility. The front-end electronics, composed of over 15000 time sampling channels, is located on the chamber. The highly integrated, custom-designed electronics and the VME-based data acquisition system are described.< >
We present the results of a search for point sources of high-energy neutrinos in the northern hemisphere using AMANDA-II data collected in the year 2000. Included are flux limits on several ...active-galactic-nuclei blazars, microquasars, magnetars, and other candidate neutrino sources. A search for excesses above a random background of cosmic-ray-induced atmospheric neutrinos and misreconstructed downgoing cosmic-ray muons reveals no statistically significant neutrino point sources. We show that AMANDA-II has achieved the sensitivity required to probe known TeV gamma-ray sources such as the blazar Markarian 501 in its 1997 flaring state at a level where neutrino and gamma-ray fluxes are equal.
We report the first measurement of the parity-violating single-spin asymmetries for midrapidity decay positrons and electrons from W{sup +} and W{sup -} boson production in longitudinally polarized ...proton-proton collisions at {radical}(s)=500 GeV by the STAR experiment at RHIC. The measured asymmetries, A{sub L}{sup W+}=-0.27{+-}0.10(stat.){+-}0.02(syst.){+-}0.03(norm.) and A{sub L}{sup W-}=0.14{+-}0.19(stat.){+-}0.02(syst.){+-}0.01(norm.), are consistent with theory predictions, which are large and of opposite sign. These predictions are based on polarized quark and antiquark distribution functions constrained by polarized deep-inelastic scattering measurements.
The contribution of B meson decays to nonphotonic electrons, which are mainly produced by the semileptonic decays of heavy-flavor mesons, in p+p collisions at {radical}(s)=200 GeV has been measured ...using azimuthal correlations between nonphotonic electrons and hadrons. The extracted B decay contribution is approximately 50% at a transverse momentum of p{sub T{>=}}5 GeV/c. These measurements constrain the nuclear modification factor for electrons from B and D meson decays. The result indicates that B meson production in heavy ion collisions is also suppressed at high p{sub T}.
Data from the first physics run at the Relativistic Heavy-Ion Collider at Brookhaven National Laboratory, Au+Au collisions at sqrts(NN)=130 GeV, have been analyzed by the STAR Collaboration using ...three-pion correlations with charged pions to study whether pions are emitted independently at freeze-out. We have made a high-statistics measurement of the three-pion correlation function and calculated the normalized three-particle correlator to obtain a quantitative measurement of the degree of chaoticity of the pion source. It is found that the degree of chaoticity seems to increase with increasing particle multiplicity.
The mass composition of high-energy cosmic rays at energies above 1015 eV can provide crucial information for the understanding of their origin. Air showers were measured simultaneously with the ...SPASE-2 air shower array and the AMANDA-B10 Cherenkov telescope at the South Pole. This combination has the advantage to sample almost all high-energy shower muons and is thus a new approach to the determination of the cosmic ray composition. The change in the cosmic ray mass composition was measured versus existing data from direct measurements at low energies. Our data show an increase of the mean log atomic mass 〈lnA〉 by about 0.8 between 500 TeV and 5 PeV. This trend of an increasing mass through the “knee” region is robust against a variety of systematic effects.
Currently recommended surgical techniques to treat severe biaxial feline talocrural soft-tissue injuries commonly lead to unsatisfactory outcome. Data relating to canine talocrural stabilisation may ...not be useful in cats due to major differences in tarsal anatomy between the species. This experimental biomechanical cadaveric study used specimens (n = 10) prepared from the distal pelvic limbs of five adult cats. The aim was to design a technique for treating talocrural luxation using suture prostheses and bone tunnels, and to investigate its suitability for use in clinical cases. Four prosthetic ligaments were placed through a series of five 1.5 mm bone tunnels. Two prostheses, the caudoproximal pair, were taut in talocrural flexion and two prostheses, the craniodistal pair, were taut in extension. The intact specimens had their range-of-motion (ROM) and stability tested, after which they were transected at the talocrural joint (simulated luxation) and repaired using the technique described. The ROM and stability of the repaired specimens were tested and compared to the intact specimens. The repaired specimens had comparable stability to the intact specimens, although the ROM was different (p <0.05) in six of 16 positions (p <0.003125). These corresponded to the positions where the lateral prostheses were taut. The repair technique described may be useful in the treatment of talocrural luxation, as it is low-profile in an area of limited soft-tissue cover, allows anatomic reduction, restores normal talocrural joint stability and near-normal tarsal ROM.
Density dependent feedback, based on cumulative population size, has been advocated to explain and mathematically characterize “boom and bust” population dynamics. Such feedback results in a ...bell-shaped population trajectory of the population density. Here, we note that this trajectory is mathematically described by the logistic probability density function. Consequently, the cumulative population follows a time trajectory that has the same shape as the cumulative logistic function. Thus, the Pearl–Verhulst logistic equation, widely used as a phenomenological model for density dependent population growth, can be interpreted as a model for cumulative rather than instantaneous population. We extend the cumulative density dependent differential equation model to allow skew in the bell-shaped population trajectory and present a simple statistical test for skewness. Model properties are exemplified by fitting population trajectories of the soybean aphid,
Aphis glycines. The linkage between the mechanistic underpinnings of the logistic probability density function and cumulative distribution function models could open up new avenues for analyzing population data.
Liquid Xe TPCs are among the most popular choices for double beta decay and WIMP dark matter searches. Gaseous Xe has intrinsic advantages when compared to Liquid Xe, specifically, tracking ...capability and better energy resolution for double beta decay searches. The performance of gaseous Xe can be further improved by molecular additives such as trimethylamine(TMA), which are expected to (1) cool down the ionization electrons, (2) convert Xe excitation energy to TMA ionizations through Penning transfer, and (3) produce scintillation and electroluminescence light in a more easily detectable wavelength (300 nm). These features may provide better tracking and energy resolution for double-beta decay searches. They are also expected to enhance columnar recombination for nuclear recoils, which can be used for searches for WIMP dark matter with directional sensitivity. We constructed a test ionization chamber and successfully measured scintillation and ionization yields at high precision with various Xe and TMA mixtures and pressures. We observed the Penning effect and an increase in recombination with the addition of TMA. However, many undesired features for dark matter searches, such as strong suppression of the scintillation light and no sign of recombination light, were also found. This work has been carried out within the context of the NEXT collaboration.
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