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arXiv · hep-lat/0404014

Light hadron spectroscopy in two-flavor QCD with small sea quark masses

PACS Collaboration·Y. Namekawa·S. Aoki·M. Fukugita·K-I. Ishikawa·N. Ishizuka·Y. Iwasaki·K. Kanaya·T. Kaneko·Y. Kuramashi·V. I. Lesk·M. Okawa·A. Ukawa·T. Umeda·T. Yoshié
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Abstract

We extend the study of the light hadron spectrum and the quark mass in two-flavor QCD to smaller sea quark mass, corresponding to $m_{PS}/m_{V}=0.60$--0.35. Numerical simulations are carried out using the RG-improved gauge action and the meanfield-improved clover quark action at $β=1.8$ ($a = 0.2$ fm from $ρ$ meson mass). We observe that the light hadron spectrum for small sea quark mass does not follow the expectation from chiral extrapolations with quadratic functions made from the region of $m_{PS}/m_{V}=0.80$--0.55. Whereas fits with either polynomial or continuum chiral perturbation theory (ChPT) fails, the Wilson ChPT (WChPT) that includes $a^2$ effects associated with explicit chiral symmetry breaking successfully fits the whole data: In particular, WChPT correctly predicts the light quark mass spectrum from simulations for medium heavy quark mass, such as $m_{PS}/m_V \simgt 0.5$. Reanalyzing the previous data %at $m_{PS}/m_{V}=0.80$--0.55 with the use of WChPT, we find the mean up and down quark mass being smaller than the previous result from quadratic chiral extrapolation by approximately 10%, $m_{ud}^{\bar{\rm MS}}(μ=2 {GeV}) = 3.11(17)$ [MeV] in the continuum limit.

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PACS Collaboration, Y. Namekawa, S. Aoki, M. Fukugita, K-I. Ishikawa, N. Ishizuka, Y. Iwasaki, K. Kanaya, T. Kaneko, Y. Kuramashi, V. I. Lesk, M. Okawa, A. Ukawa, T. Umeda, T. Yoshié. 2004-09-13. Light hadron spectroscopy in two-flavor QCD with small sea quark masses. https://doi.org/10.1103/physrevd.70.074503

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