Scanning the topological sectors of the QCD vacuum with the hybrid Monte Carlo algorithm

We address a long standing issue and determine the decorrelation efficiency of the hybrid Monte Carlo algorithm (HMC), for full QCD with Wilson fermions, with respect to vacuum topology. On the basis of five large QCD vacuum field ensembles (with 3000 to 5000 trajectories each and $m_{\pi }{/m}_{\rho }$- ratios in the range ⩾0.69, for two sea quark flavors), we are able to establish that HMC provides sufficient tunneling between the different topological sectors of QCD. This will have an important bearing on the prospect to determine, by lattice techniques, the topological susceptibility of the vacuum, and topology sensitive quantities such as the spin content of the proton, or the ${\eta }^{\prime }$ mass.