1751824
Thermodynamics of lattice QCD with two light quarks on a 16(3) x 8 lattice.
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
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.
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}
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.
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.
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.
13473472
Decay distribution of high-transverse-momentum rho mesons.
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.
37501749
Search for direct CP violation in nonleptonic decays of charged Xi and lambda hyperons
A search for direct CP violation in the nonleptonic decays of hyperons has been performed. In comparing the product of the decay parameters, alpha(Xi)alpha(Lambda), in terms of an asymmetry parameter, A(XiLambda), between hyperons and antihyperons in the charged Xi-->Lambdapi and Lambda-->ppi decay sequence, we found no evidence of direct CP violation. The parameter A(XiLambda) was measured to be 0.012+/-0.014.
6958720
Precise measurement of the Xi - magnetic moment.
With 4.36{times}10{sup 6} events, spin precession in a magnetic field has been used to measure the magnetic moment of the {Xi}{sup {minus}} hyperon as {minus}0.6505{plus minus}0.0025 nuclear magnetons.
28319301
Comparison of 20 exclusive reactions at large t.
We report a study of 20 exclusive reactions measured at the AGS at 5.9 GeV/[ital c] incident momentum, 90[degree] center of mass. This experiment confirms the strong quark flow dependence of two-body hadron-hadron scattering at large angle. At 9.9 GeV/[ital c] an upper limit had been set for the ratio of cross sections for ([ital [bar p]p][r arrow][ital [bar p]p])/([ital pp][r arrow][ital pp]) at 90[degree] c.m. with the ratio less than 4%. The present experiment was performed at lower energy to gain sensitivity, but was still within the fixed angle scaling region. A ratio [ital R]([ital [bar p]p]/[ital pp])[approx]1/40 was measured at 5.9 GeV/[ital c], 90[degree] c.m. in comparison to a ratio near 1.7 for small angle scattering. In addition, many other reactions were measured, often for the first time at 90[degree] c.m. in the scaling region, using beams of [pi][sup [plus minus]], [ital K][sup [plus minus]], [ital p] and [ital [bar p]] on a hydrogen target. There are similar large differences in cross sections for other reactions: [ital R]([ital K][sup [minus]][ital p][r arrow][pi][sup +][Sigma][sup [minus]]/[ital K][sup [minus]][ital p][r arrow][pi][sup [minus]][Sigma][sup +])[approx]1/12, for example. The relative magnitudes of the different cross sections are consistent with the dominance of quark interchangemore » in these 90[degree] reactions, and indicate that pure gluon exchange and quark-antiquark annihilation diagrams are much less important. The angular dependence of several elastic cross sections and the energy dependence at a fixed angle of many of the reactions are also presented.« less