K.D. Born

The hadron spectrum in QCD with dynamical staggered fermions

The hadron spectrum has been calculated in a large scale simulation of QCD with dynamical staggered fermions on a 16(3) x 24 lattice at m = 0.01 and beta = 5.35 and 5.15. Special emphasis is placed on flavour symmetry restoration, for which we observe a substantial improvement between the two beta-values. The results at the lower beta-value provide a scale for the critical temperature on an eight time slice lattice. In addition to the spectrum we investigate chiral properties and calculate the chiral condensate and f(pi) in the chiral limit.

The interquark potential: a QCD lattice analysis

We report on a QCD analysis of the potential between heavy quarks. Our calculation includes light quark loops and is carded out on a 163 x 24 lattice for couplings fl = 5.35 and 5.15 and a quark mass amq = 0.010. We generated lattice configurations using a hybrid Monte Carlo algorithm for Ne = 4 flavors of staggered fermions. We can explore distances between 0.12 fm and 0.9 fm for these parameters. The shape of the resulting potential is well described by the superposition of a term proportional to 1/R and a linear confinement potential. This full QCD potential is compared to results obtained from quenched approximation simulations on lattices of the same size and with the same value of the cutoff. We discuss a rough estimate of the QCD coupling.

The interquark potential

Abstract We report on a measurement of the potential between static quarks in full lattice QCD at small quark masses. The calculation is carried out on a 24 × 163 lattice at β = 5.35 and 5.15 with a quark mass am = 0.010 employing the hybrid Monte Carlo method for NF = 4 dynamical fermions. The results are compared to the potential calculated in the quenched approximation on the same size lattice in a β range from 5.7 to 6.0. Screening effects and the ambiguities in β-shifts for observables such as hadron masses, the quark condensate and the string tension will be discussed.

Spin dependence of the heavy-quark potential: a QCD lattice analysis

Abstract We have investigated the spin dependence of the potential between heavy quarks in full lattice QCD, including the effects of light quark loops. The form of the spin-orbit, the tensor and the spin-spin forces present clear evidence for long-range scalar confinement supplemented by a Coulomb force at short distances. This agrees with observations from quarkonium spectroscopy. The QCD simulation has been carried out for Kogut-Susskind fermions with four degrees of freedom at a gauge coupling β = 5.35 and a quark mass am q = 0.01 on a 16 3 × 24 size lattice. This corresponds to a lattice spacing 0.12 fm, a spatial lattice size of about 2 fm and a light quark mass of 48 MeV.

QCD WITH DYNAMICAL FERMIONS

Abstract We present our latest hadron mass calculations for four flavors of staggered fermions on a 24 × 163 lattice at quark mass ma = 0.010 and β = 5.35. Our work clearly shows a systematic tendency for the nucleon to ϱ meson mass ratio to decrease below the naive quark model value of 3 2 as the zero quark mass limit is approached. This completes an extensive study of hadron spectroscopy using the pseudofermion method at numerous quark mass values for β = 5.20 and β = 5.35. We also present initial results of our new Hybrid Monte Carlo analysis at β = 5.35 and ma = 0.025 on the 24 × 163 lattice. We discuss the performance of the algorithm on this lattice, and we measure hadron masses and the interquark potential. Where we can compare results, we find good agreement with our earlier pseudofermion calculations.

Hadrons in unquenched lattice QCD

Incorporating dynamical Kogut-Susskind fermions (NF = 4) into a Monte Carlo simulation of QCD, we have analyzed the masses of low lying hadrons, chiral symmetry breaking and the interquark potential. We used a 24 × 123 lattice for two couplings β = 5.20 and 5.35; quarkk masses varied from m = 0.075 down to 0.010. We find good agreement between the results from our pseudofermion method and those reported from a hybrid simulation at [β, m] = [5.20, 0.050].

Hadron Masses, Chiral Symmetry Breaking and the Interquark Potential in Lattice QCD

Incorporating dynamical Kogut-Susskind fermions into a Monte Carlo simulation of QCD, we have analyzed the masses of low lying hadrons, chiral symmetry breaking and the interquark potential. We used a 24 x 123 lattice for two couplings g, where β = 6/g 2 = 5.20 and 5.35. Quark masses were ma = 0.075,0.050 and 0.025 [a being the lattice spacing]. In additon, first results from runs at (s = 5.20 and ma = 0.010 will be discussed.

Renormalisation of lattice currents and the calculation of decay constants for dynamical staggered fermions

A numerical calculation of the lattice staggered renormalisation constants at beta = 5.35, m = 0.01 is presented. It is seen that there are considerable non-perturbative effects present. As an application the vector decay constant f(rho) is estimated.