Zusammenfassung
We present an update of our analysis [1] which includes additional ensembles at different quark masses, lattice spacings and volumes, all with high statistics. We use N-f = 2 mass-degenerate quark flavors, employing the nonperturbatively improved clover action. The lattice matrix elements are converted to the MS scheme via renormalization factors determined nonperturbatively in the RI'-MOM ...
Zusammenfassung
We present an update of our analysis [1] which includes additional ensembles at different quark masses, lattice spacings and volumes, all with high statistics. We use N-f = 2 mass-degenerate quark flavors, employing the nonperturbatively improved clover action. The lattice matrix elements are converted to the MS scheme via renormalization factors determined nonperturbatively in the RI'-MOM scheme. We have systematically investigated excited state contributions, in particular, at the smallest, near physical, pion mass. While our results (with much increased precision) are consistent with Ref. [1], comparing to previous determinations we find that excited state contributions can be significant if the quark smearing is not suitably optimized, in agreement with other recent studies. The difference with respect to the value for [x](u-d) extracted from experimental data is reduced but not resolved. Using lattice sizes in the range Lm(pi) similar to 3.4-6.7, no significant finite volume effects have been observed. Performing a controlled continuum limit that may remove the discrepancy will require simulations at lattice spacings a < 0.06 fm.
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