Light and strange hadron spectroscopy with dynamical Wilson fermions

Abstract

We present the final analysis of the light and strange hadron spectra from a full QCD lattice simulation with two degenerate dynamical sea quark flavours at β = 5.6 on a 16 3 × 32 lattice. Four sets of sea quark masses corresponding to the range .69 ≤ m π /m ρ ≤ .83 are investigated. For reference we also ran a quenched simulation at β eff = 6.0, which is the point of equal lattice spacing, a −1 ρ . In the light sector, we find the chiral extrapolation to physical u-and d-masses to present a major source of uncertainty, comparable to the expected size of unquenching effects. From linear and quadratic fits we can estimate the errors on the hadron masses made from light quarks to be on a 15 % level prior to the continuum extrapolation. For the hadrons with strange valence quark content, the N F = 2 approximation to QCD appears not to cure the well-known failure of quenched QCD to reproduce the physical K − K * splitting.2

Pion-nucleon σ term with dynamical Wilson fermions

“…As a cross check we compare the total value C u + C d + 2D q = 8.82(2.52) with our previous result from the quadratic extrapolation of the nucleon mass [8] ∂M N ∂m q (m ud ) = 11.7(4.9) , and find agreement. Note that the statistical uncertainty of the total amplitude obtained with the direct (ratio) method is smaller than the one from the derivative method (29% compared to 42%).…”

“…Finally, we determine the pion-nucleon σ-term in physical units. With 3 m ud = 0.000901(54) (in lattice units) and a −1 ρ = 2.30GeV [8] one obtains…”

“…This is done by identifying the masses of the sea quarks with those of the light valence quarks of the nucleon. The mass of the strange quark, which has no counterpart in the sea, is contained to match the strange hadron spectrum in semi-quenched analysis [8]. This procedure accounts at least for the influence of light sea quarks on the above matrix element and is certainly more adequate than previous quenched (n f = 0) calculations.…”

“…To obtain this data we held the loop quark fixed at the strange quark mass (c.f. [8]), and kept valence and sea quark masses degenerate under chiral extrapolation.…”

“…We have generated 200 statistically independent vacuum configurations at each of our 4 values of the sea quark mass, which correspond to m π /m ρ = 0.833(3), 0.809(15), 0.758(11) and 0.686 (11). Details of the simulation as well as the analysis of the light hadron spectrum can be found in [8].…”