The hadron spectrum from lattice QCD

Determining the hadron spectrum and hadron properties beyond the ground states is a challenge in lattice QCD. Most of these results have been in the quenched approximation but now we are entering the dynamical era. I review some of the ideas and methods of the lattice approach, concentrating on a few examples and on results obtained for Chirally Improved (CI) fermions.     

Calculation of the hadron spectrum in lattice QCD

We present Monte Carlo results for the hadron mass-spectrum in lattice SU(3) using the Wilson action and the quenched approximation. We show that on a 6³· 10 lattice at β=6.0, there exist long-lived metastable states of the gauge-field, characterized by the eigenvalues of Z(3) and associated with the first-order deconfining phase transition. The hadron masses are very different in these state if the quark paths that wind around the lattice are not removed. We demonstrate two methods which eliminate a significant fraction of such quark paths. The final results for hadron masses do not agree with the experimental values. We find that the π and ?, as well as the proton and the Δ are degenerate.     

Precise hadron mass calculations from lattice QCD

By using scalar as opposed to spin-$\text{1}\text{2}$ quarks and treating spin effects perturbatively, the masses of the lowest lying 0^- and 1^- mesons above 1 GeV (the J/Ψ, η_c, D, D¹, F, F¹, and φ) are calculated to 1%. The masses of the K¹, ?, and K are respectively obtained to 3%, 8% and 30%. Certain (spin-averaged) linear combinations of baryon masses are also computed. The nucleon-delta result differs from experiment by 8%. For heavier baryons the error is smaller. Scalar lattice QCD seems to be a promising approach to the strong interactions.     

Interacting hadron resonance gas meets lattice QCD

We present, in the framework of the interacting hadron resonance gas, an evaluation of thermodynamical quantities. The interaction is modelled via a correction for the finite size of the hadrons. We investigate the sensitivity of the model calculations on the radius of the hadrons, which is a parameter of the model. Our calculations for thermodynamical quantities as energy and entropy densities and pressure are confronted with predictions using the lattice Quantum Chromodynamics (QCD) formalism.     

Hadron spectroscopy in lattice QCD

A Monte Carlo computation of meson and hadron spectroscopy within lattice QCD is made. We give a detailed discussion of the statistical and systematic errors of the results and analyze the present limitations of our approach. The results are in agreement with the observed spectrum. We also estimate the values of up, down and strange quark masses.     

Hadron spectroscopy from lattice QCD

I present recent developments in the lattice QCD calculations of the light hadron spectrum. Emphasis is placed on the failure of the quenched approximation in reproducing the observed spectrum and indications that the discrepancy is reduced by introducing two flavors of light dynamical quarks.     

Extraction of hadron interactions above inelastic threshold in lattice QCD

We propose a new method to extract hadron interactions above inelastic threshold from the Nambu-Bethe-Salpeter amplitude in lattice QCD. We consider the scattering such as A + B → C + D, where A, B, C, D are names of different 1-particle states. An extension to cases where particle productions occur during scatterings is also discussed.     

The calculation of the hadron spectrum in lattice QCD with dynamical quarks

Hadron masses are calculated on an 8³×16 lattice using four flavors of staggered fermions to generate the gauge configurations, but using Wilson fermions to calculate the hadron propagators. The identification of a value of the Wilson hopping parameter with the value of the bare quark mass used in the simulations is discussed.     

Analytic calculation of hadron spectra by random-walk approximations in lattice QCD

We explain the detail of how to calculate the meson and baryon spectrum by a random walk approximation analytically. The results are compared with experimental values and Monte Carlo results.