  A central hypothesis in the theory of cataclysmic variable (CV) evolution is
the need to explain the observed lack of accreting systems in the ~2-3 h
orbital period range, known as the period gap. The standard model, disrupted
magnetic braking (DMB), reproduces the gap by postulating that CVs transform
into inconspicuous detached white dwarf (WD) plus main sequence (MS) systems,
which no longer resemble CVs. However, observational evidence for this standard
model is currently indirect and thus this scenario has attracted some criticism
throughout the last decades. Here we perform a simple but exceptionally strong
test of the existence of detached CVs (dCVs). If the theory is correct dCVs
should produce a peak in the orbital period distribution of detached close
binaries consisting of a WD and an M4-M6 secondary star. We measured six new
periods which brings the sample of such binaries with known periods below 10 h
to 52 systems. An increase of systems in the ~2-3 h orbital period range is
observed. Comparing this result with binary population models we find that the
observed peak can not be reproduced by PCEBs alone and that the existence of
dCVs is needed to reproduce the observations. Also, the WD mass distribution in
the gap shows evidence of two populations in this period range, i.e. PCEBs and
more massive dCVs, which is not observed at longer periods. We therefore
conclude that CVs are indeed crossing the gap as detached systems, which
provides strong support for the DMB theory.
