Nuclear transparency to large-angle pp elastic scattering.
Large-angle pp elastic and quasielastic (p,2p) scattering have been simultaneously observed in hydrogen and each of several nuclear targets (Li, C, AL, Cu, Pb) at incident proton momenta of 6, 10, and 12 GeV/c. The nuclear transparency is the ratio of such a cross section in a nucleus to the free pp cross section. The transparency of aluminum increases with incident momentum by more than a factor of 2 from 6 to 9.5 GeV/c and falls significantly between 9.5 and 12 GeV/c. This occurs in a region where the free-proton nucleon-absorption cross section exhibits little energy dependence. QCD predicts an increase in transparency with energy.

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: Effects of spatial size, lattice doubling, and source operators on the hadron spectrum with dynamical staggered quarks at 6/g2=5.6.
abstract: We have extended our previous study of the lattice QCD spectrum with two flavors of staggered dynamical quarks at 6/[ital g][sup 2]=5.6 and [ital am][sub [ital q]]=0.025 and 0.01 to larger lattices, with better statistics and with additional sources for the propagators. The additional sources allowed us to estimate the [Delta] mass and to measure the masses of all mesons whose operators are local in time. These mesons show good evidence for flavor symmetry restoration, except for the masses of the Goldstone and non-Goldstone pions. PCAC is observed in that [ital m][sub [pi]][sup 2][proportional to][ital m][sub [ital q]], and [ital f][sub [pi]] is estimated. Use of undoubled lattices removes the problems with the pion propagator found in our earlier work. Previously we found a large change in the nucleon mass at a quark mass of [ital am][sub [ital q]]=0.01 when we increased the spatial size from 12 to 16. No such effect is observed at the larger quark mass, [ital am][sub [ital q]]=0.025. Two kinds of wall source were used, and we have found difficulties in getting consistent results for the nucleon mass between the two sources.

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: Comparison of lattice Coulomb-gauge wave functions in the quenched approximation and with dynamical fermions.
abstract: We present a comparison of Coulomb-gauge wave functions from 6/[ital g][sup 2]=6.0 quenched simulations with two simulations which include the effects of dynamical fermions: simulations with two flavors of dynamical staggered quarks and valence Wilson quarks at 6/[ital g][sup 2]=5.6 and simulations with two flavors of dynamical Wilson quarks and Wilson valence quarks at 6/[ital g][sup 2]=5.3. The spectroscopy of these systems is essentially identical. Parametrizations of the wave functions are presented which can be used as interpolating fields for spectroscopy calculations. The sizes of particles are calculated using these parametrized wave functions. The resulting sizes are small, approximately half the sizes of the physical states. The charge radius of the neutron, which provides an indication of the asymmetries between the wave functions of up and down quarks, is calculated. Although the size of the nucleon in these simulations is small, the ratio of the charge radius of the neutron to that of the proton is consistent with the physical value. We find no significant differences between the quenched and dynamical simulations.

title: Thermodynamics of lattice QCD with two light quarks on a 16(3) x 8 lattice.
abstract: We have carried out a numerical study of the high-temperature behavior of lattice QCD with two flavors of staggered quarks. Our simulations were performed on 16 3 × 8 lattices with a quark mass m q = 0.0125, in units of the inverse lattice spacing. By monitoring the Wilson-Polyakov line, the chiral order parameter , and the average plaquette, we have determined that a crossover between the low-temperature state of ordinary hadronic matter and the high-temperature quark-gluon plasma occurs at a gauge coupling of 6/g 2 = 5. 54(2). Thermodynamic quantities do not show a large jump, although the equilibration time becomes quite long in the vicinity of the crossover. We have measured the entropy densities in the neighborhood of the crossover and further into the plasma phase

title: SU(2) beta function with and without dynamical fermions.
abstract: We study the ..beta.. function of SU(2) lattice gauge theory in the presence and absence of dynamical fermions with the (improved) ''ratio method.'' The pseudofermion algorithm used to simulate the fermion action seems to be capable of giving the right contribution to the ..beta.. function. For two flavors of fermions we find agreement with asymptotic scaling to within approx.15% for ..beta..> or approx. =2.0