Finite temperature QCD with four light quark flavours

QCD with four light flavours of dynamical staggered quarks (m=0.025 lattice units) was simulated on a 123x4 lattice using the hybrid algorithm. We found clear evidence for a first order transition to a quark-gluon plasma. This is in agreement with simulations on smaller lattices (up to 83x4). This contrasts with the intermediate mass range (m> or approx.0.1) where transitions seen on smaller lattices appear to be a finite size effect rather than true first order transitions. (orig.)