Compressibility of a two-dimensional hole gas in a tilted magnetic field

We have measured compressibility of a two-dimensional hole gas in $p-{\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructure, grown on a (100) surface, in the presence of a tilted magnetic field. It turns out that the parallel component of magnetic field affects neither the spin splitting nor the density of states. We conclude that (a) g factor in the parallel magnetic field is nearly zero in this system, and (b) the level of the disorder potential is not sensitive to the parallel component of the magnetic field.