Hard scattering with exclusive reactions: pi -p elastic scattering and rho -meson production.

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

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

title: Hadron spectrum in QCD with valence Wilson fermions and dynamical staggered fermions at 6/g2=5.6.
abstract: We present an analysis of hadronic spectroscopy for Wilson valence quarks with dynamical staggered fermions at a lattice coupling 6/{ital g}{sup 2}={beta}=5.6 at a sea-quark mass of {ital am}{sub {ital q}}=0.01 and 0.025, and of Wilson valence quarks in the quenched approximation at {beta}=5.85 and 5.95, both on 16{sup 3}{times}32 lattices. We make comparisons with our previous results with dynamical staggered fermions at the same parameter values but on 16{sup 4} lattices doubled in the temporal direction.

title: Monte Carlo renormalization-group investigation of the two-dimensional O(4) sigma model.
abstract: An improved Monte Carlo renormalization-group method is used to determine the ..beta.. function of the two-dimensional O(4) sigma model. While for (inverse) couplings ..beta..approx. >2.2 one obtains agreement with asymptotic scaling according to asymptotic freedom, one can see deviations from it at smaller couplings. They are, however, consistent with the behavior of the correlation length, indicating ''scaling'' according to the full ..beta.. function. These results contradict recent claims that the model has a critical point at finite coupling.

title: B spectroscopy from NRQCD with dynamical fermions.
abstract: We present a lattice investigation, partially including the effects of dynamical quarks, of the heavy-light mesons using NRQCD for the heavy quark and the Wilson action for the light quark. We perform an extensive calculation of the spectrum employing a multistate, multiexponential fitting analysis which enables us to extract the 2{ital S}-1{ital S} splitting as well as the {sup 1}{ital P}{sub 1}-{ital {bar S}} and hyperfine splittings. The Wilson action introduces a large systematic error into the calculation, and within this uncertainty we obtain agreement with experiment. We perform a comprehensive calculation of the heavy-light meson mass, investigating three methods and their range of validity. The agreement found between these methods confirms that Lorentz invariance can be restored at this order in NRQCD by a constant shift to all masses. We calculated spectroscopic quantities over a wide range in heavy quark mass and are able to perform a detailed investigation of heavy quark symmetry around the {ital b} quark mass. In particular, we extract the nonperturbative coefficients of terms in the heavy quark expansion of the meson binding energy. We demonstrate the importance of using tadpole-improved operators in such a calculation.

title: More on the two-dimensional O(4) sigma model.
abstract: New measurements of the correlation length and magnetic susceptibility for the two-dimensional O(4) sigma model are reported. They corroborate the conclusion from a recent Monte Carlo renormalization-group investigation that the standard, asymptotic-freedom picture holds for this model. A finite-size scaling analysis also supports this conclusion.

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