The Light Hadron Mass Spectrum with Non-Perturbatively O(a) Improved   Wilson Fermions
  We compute the light hadron mass spectrum in quenched lattice QCD at $\beta = 6.0$ using the Sheikholeslami-Wohlert fermionic action. The calculation is done for several choices of the coefficient $c_{SW}$, including $c_{SW} = 0$ and the recently proposed optimal value $c_{SW} = 1.769$. We find that the individual masses change by up to 30\% under $O(a)$ improvement. The spectrum calculation suggests $c_{SW} \approx 1.4$ for the optimal value of the coefficient. 
M. G\"ockeler, R. Horsley, H. Perlt, P. Rakow, G. Schierholz, A.   Schiller and P. Stephenson