39465789
Effects of spatial size, lattice doubling, and source operators on the hadron spectrum with dynamical staggered quarks at 6/g2=5.6.
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.
119542063
Study of chiral symmetry in quenched QCD using the overlap Dirac operator
We compute fermionic observables relevant to the study of chiral symmetry in quenched QCD using the overlap Dirac operator for a wide range of fermion mass. We use analytical results to disentangle the contribution from exact zero modes and simplify our numerical computations. Details concerning the numerical implementation of the overlap Dirac operator are presented. {copyright} {ital 1999} {ital The American Physical Society}
119548610
Biased Metropolis-heat-bath algorithm for fundamental-adjoint SU(2) lattice gauge theory
For SU(2) lattice gauge theory with the fundamental-adjoint action an efficient heat-bath algorithm is not known so that one had to rely on Metropolis simulations supplemented by overrelaxation. Implementing a novel biased Metropolis-heat-bath algorithm for this model, we find improvement factors in the range 1.45 to 2.06 over conventionally optimized Metropolis simulations. If one optimizes further with respect to additional overrelaxation sweeps, the improvement factors are found in the range 1.3 to 1.8.
14897456
Divergent chiral condensate in the quenched Schwinger model
We calculate numerically the eigenvalue distribution of the overlap Dirac operator in the quenched Schwinger model on a lattice. The distribution does not fit any of the three universality classes of spontaneous chiral-symmetry breaking, and its strong volume dependence indicates that the chiral condensate in the quenched theory is an ill-defined and divergent quantity. When we reweight configurations with the Dirac determinant to study the theory with N{sub f}=1, we obtain a distribution of eigenvalues that is well-behaved and consistent with the theory of explicit symmetry breaking due to the anomaly.
15338965
Infrared and ultraviolet properties of the Landau gauge quark propagator
Abstract We present a current summary of a program to study the quark propagator using lattice QCD. We use the Overlap and “Asqtad” quark actions on a number of lattice ensembles. to assess systematic errors. We comment on the place of this work amongst studies of QCD Green's functions in other formulations. A preliminary calculation of the running quark mass is presented.
121063312
Search for symmetry restoration in the fundamental SU(2) Higgs model
Abstract The phase structure of the fundamental SU(2) Higgs model at finite temperature is investigated close to the zero-temperature Higgs transition by Monte Carlo methods. In the confined phase at zero temperature we find a crossover from a confined to a deconfined region that remains quite sharp on lattices of temporal extent NT = 4 even close to the Higgs transition. On asymmetric lattices the Higgs transition shifts slightly compared to the zero-temperature, symmetric lattice, giving indirect evidence for symmetry restoration at high temperature.
42810293
Comparison of exclusive reactions at large t.
Cross sections or upper limits are reported for 12 meson-baryon and two baryon-baryon reactions for an incident momentum of 9.9 GeVc, near 90/sup 0/ c.m.: ..pi../sup +- /p..-->..p..pi../sup +- /,pp/sup +- /,..pi../sup +0//sup +- /,K/sup +/)Sigma)/sup +- /, (..lambda../sup 0/)Sigma)/sup 0/)K/sup 0/;K/sup +- /p..-->..pK/sup +- /;p/sup +- /p..-->..pp. By studying the flavor dependence of the different reactions, we have been able to isolate the quark-interchange mechanism as dominant over gluon exchange and quark-antiquark annihilation
12748479
Evidence for time and directional enhancements of multimuon cosmic-ray events.
We have observed 1.05 x 10/sup 6/ single-muon and 6869 multimuon events deep underground with the Soudan 1 nucleon-decay detector. The single-muon flux is consistent with isotropy and with results of previous experiments. We have found indications of bursts of multimuon events, particularly from a direction near Cygnus X-3. These bursts arrive from an extended angular region of 30/sup 0/ x 30/sup 0/. The size of the angular region and the lack of a corresponding effect in the single-muon events are difficult to understand. In addition, there is weaker evidence for an excess in the time-integrated multimuon flux near the north galactic pole. We have evaluated the possibility that these effects are caused by random or systematic errors.
45078944
Measurements of production polarization and decay asymmetry for Xi - hyperons.
35246664
Polarization of Omega - hyperons produced in 800 GeV proton-beryllium collisions.
The polarization of 103 211 [Omega][sup [minus]] hyperons produced in 800 GeV proton-beryllium inclusive reactions has been measured. Between 0.3[lt][ital x][sub [ital F]][lt]0.7 and 0.5[lt][ital p][sub [ital t]][lt]1.3 GeV/[ital c], the [Omega][sup [minus]] polarization is found to be consistent with zero, with a mean value of [minus]0.01[plus minus]0.01 at [l angle][ital x][sub [ital F]][r angle]=0.5 and [l angle][ital p][sub [ital t]][r angle]=0.95 GeV/[ital c]. This behavior is similar to that of [bar [Lambda]][sup 0], which also does not have any quarks in common with the incident proton, but is different from [bar [Xi]][sup +], which is significantly polarized in the same kinematic region.
32857126
Polarization of Xi - and Omega - hyperons produced from neutral beams.