QCD sum rule for S-11(1535)

We propose a new interpolating field for S-11(1535) to determine its mass from QCD sum rules. In the nonrelativistic limit, this interpolating field dominantly reduces to two quarks in the s-wave state and one quark in the p-wave state. An optimization procedure, which makes use of a duality relation, yields the interpolating field which overlaps strongly with the negative-parity baryon and at the same time does not couple at all to the low-lying positive-parity baryon. Using this interpolating field and applying the conventional QCD sum rule analysis, we find that the mass of S-11 is reasonably close to the experimentally known value, even though the precise determination depends on the poorly known quark-gluon condensate. Hence our interpolating field can be used to investigate the spectral properties of S-11(1535).