Decay distribution of high-transverse-momentum rho mesons.

title: HARD QUARK-QUARK SCATTERING WITH EXCLUSIVE REACTIONS*
abstract: We have begun a program designed to study hard quark-quark scattering with exclusive reactions, focusing on quasi-elastic two-body reactions with all possible quark flavor exchanges. Examples are ..pi../sup -/p ..-->.. ..pi../sup -/p, rho/sup -/p, ..pi../sup +/..delta../sup -/, K/sup +/..sigma../sup -/, or K..lambda... Of the two-body exclusives, only elastic scattering had been measured at such large t previous to our experiment. By comparing the relative importance of different final states, the energy dependence of the production ratios of these states, the prominence of resonances such as rho/sup -/ over background in this region, and measuring polarizations where accessible, we have collected a large body of data on hard scattering in a completely new domain. Previously, essential all short distance QCD tests have been for inclusive processes. We have taken data with both negative and positive incident beam at 10 GeV/c on a hydrogen target and will present the first results, for ..pi../sup -/p ..-->.. ..pi../sup -/p and rho/sup -/p at THETA/sub cm/ = 90/sup 0/, -t = 9 GeV/sup 2//c/sup 2/. The apparatus consists of a magnetic spectrometer, with Cerenkov particle identification, which selects stable charged particles (protons in this case) at high momentum near 90/sup 0/ in the center-of-mass. Amore » large aperture array of PWCs observes the recoil particle or charged decay products. Cross sections are extremely low, approximately a 1 nb/(GeV/c)/sup 2/ for elastic scattering. We will report on a sample of more than 1000 ..pi../sup -/p elastic events, and on rho/sup -/p, where the rho/sup -/ decay distribution was observed. We find a surprisingly large rho/sup -/p cross section in this large momentum transfer region, with rho/sup -/p about half the elastic cross section, and a striking spin alignment of the rho/sup -/.« less

title: Measurements of production polarization and decay asymmetry for Xi - hyperons.

title: New limit on magnetic monopole flux
abstract: The underground Soudan-1 nucleon decay experiment can measure the velocities of slowly moving particles if they can be detected by ionization at a level 0.5 times that of a relativistic muon. Magnetic monopoles predicted by grand unified theories should satisfy this condition if their velocities are greater than 10/sup -3/c. During a live time of 0.41 yr, no candidate has been observed, implying a 90%- confidence-level limit on the flux of such objects of <4.1 x 10/sup -13/ cm/sup -2/ sr/sup -1/ s/sup -1/ for velocities between 10/sup -3/c and 10/sup -2/c.

title: A MULTIKILOTON DETECTOR TO CONDUCT A SENSITIVE SEARCH FOR NUCLEON DECAY

title: Study of quark flow in exclusive reactions at 90 degrees in the center of mass (AGS E838)
abstract: We report a study of quark flow in 20 exclusive reactions measured at Brookhaven National Laboratory’s AGS with a beam momentum of 5.9 GeV/c at 90° in the center of mass. This experiment confirms the strong quark flow reaction mechanism dependence of two‐body hadron scattering at large angles seen at 9.9 GeV/c. Large differences in cross sections for different reactions are consistent with the dominance of quark interchange in these 90° reactions, and indicate that pure gluon exchange and quark/antiquark annihilation diagrams are less important.

title: Properties of the a1 meson from lattice QCD.
abstract: We determine the mass and decay constant of the $a_1$ meson using Monte Carlo simulation of lattice QCD. We find $M_{a_1} = 1250 \pm 80$ MeV and $f_{a_1} = 0.30 \pm 0.03 ~({\rm GeV})^2$, in good agreement with experiment.

title: Hadron spectrum and matrix elements in QCD with dynamical Wilson fermions at 6/g2=5.3.
abstract: We present results of a lattice simulation of quantum chromodynamics with two degenerate flavors of dynamic Wilson fermions at $\frac{6}{{g}^{2}}=5.3$ at each of two dynamical fermion hopping parameters $\ensuremath{\kappa}=0.1670 \mathrm{and} 0.1675$ corresponding to pion masses in lattice units of about 0.45 and 0.31. The simulations include three other values of valence quark mass, in addition to the dynamical quarks. We present calculations of masses and of the decay constants of vector mesons and of pseudoscalars, including the $D$-meson decay constant. The effects of sea quarks on matrix elements and spectroscopy are small.

title: QCD beta function with two flavors of dynamical Wilson fermions.
abstract: We test the asymptotic scaling behavior of state-of-the-art simulations of QCD with two flavors of light Wilson fermions. This is done by matching {pi} and {rho} masses on lattices of size 16{sup 3}{times}32 and 8{sup 3}{times}16. We find that at {beta}=6/{ital g}{sup 2}=5.3 matching is not possible over a range extending down to {beta}=3.5. The large lattice data at {beta}=5.5 matches the small lattice values at {beta}=4.9(1) leading to a shift {Delta}{beta}=0.6(1), considerably larger than the perturbative prediction of 0.45. In both cases we conclude that the simulations are very far from the asymptotic scaling region.

title: Overrelaxation and mode coupling in sigma models.
abstract: An exact overrelaxation algorithm for nonlinear \ensuremath{\sigma} models is presented and practically implemented. Using a new method of analysis the mode-mode coupling mechanism underlying overrelaxation is clearly exhibited. In one dimension our numerical results provide evidence that the critical exponent z is equal to unity.

title: Dynamics of multidimensional generalization of Bianchi type-IX cosmological models.
abstract: We investigate the dynamics of an 11-dimensional homogeneous cosmological model. We assume that the t = const hypersurfaces are products of a 3-dimensional Bianchi type-IX space and a 7-dimensional torus. Most results of our investigation hold when the 7-dimensional torus is replaced by an m-dimensional torus T/sup m/. We show that for a large class of vacuum solutions the physical space expands while the microspace contracts providing a natural mechanism of dimensional reduction. Matter satisfying a simple barotropic equation of state always breaks the process of dynamical dimensional reduction. With special attention we study the behavior of our model close to the initial singularity. In contrast with the 4-dimensional Bianchi type-IX cosmological model the Kasner solution always describes an approach to the initial singularity. We study the transition from the Kasner regime to the oscillatory regime. We show that matter does not significantly change this property. We have found some exact solutions; they describe isotropic physical space, and axially symmetric physical space. We also investigate high-temperature quantum effects and their effects on the dynamics of our model. We show that the high-temperature quantum corrections do not depend on the geometrical properties of space, provided it is compact. The high-temperature quantummore » corrections can be described by a macroscopic equation of state satisfied by radiation.« less