Valence quarks in the QCD plasma: Quark number susceptibilities and screening

We investigate the quark sector of quenched QCD for 1.5less than or equal toT/T(c)less than or equal to3 in the continuum limit, using two different lattice discretizations of quarks and extrapolating from lattice spacings between 1/4T and 1/14T. At these temperatures, the flavor off-diagonal susceptibility chi(ud)/T-2 is compatible with zero at each lattice spacing, and hence also in the continuum limit. In the continuum limit, the light quark susceptibilities are about 10% less than the ideal gas results even at the highest T, in agreement with hard thermal loop predictions but marginally below a resummed perturbative computation. For the mass range appropriate to the strange quark, the flavor diagonal susceptibility is significantly smaller. Our estimate of the Wroblewski parameter is compatible with observations at BNL RHIC and CERN SPS. The continuum limit of screening masses in all (local) quark bilinears is very close to the ideal gas results.