Four-quark operators in hadrons
  We present calculations of matrix elements of 4-quark operators in the pion and in the nucleon extracted from quenched Monte Carlo simulations at beta = 6.0 using Wilson fermions. These operators are relevant for higher-twist effects. We are particularly careful to avoid mixing with lower-dimensional operators by choosing appropriate flavour structures. 
S. Capitani, M. Gockeler, R. Horsley, B. Klaus, W. Kurzinger, D.   Petters, D. Pleiter, P.E.L. Rakow, S. Schaefer, A. Schafe...