  For transiting planets, the Rossiter-McLaughlin effect allows the measurement
of the sky-projected angle beta between the stellar rotation axis and a
planet's orbital axis. Using the HARPS spectrograph, we observed the
Rossiter-McLaughlin effect for six transiting hot Jupiters found by the WASP
consortium. We combine these with long term radial velocity measurements
obtained with CORALIE. We found that three of our targets have a projected
spin-orbit angle above 90 degrees: WASP-2b: beta = 153 (+11 -15), WASP-15b:
beta = 139.6 (+5.2 -4.3) and WASP-17b: beta = 148.5 (+5.1 -4.2); the other
three (WASP-4b, WASP-5b and WASP-18b) have angles compatible with 0 degrees.
There is no dependence between the misaligned angle and planet mass nor with
any other planetary parameter. All orbits are close to circular, with only one
firm detection of eccentricity on WASP-18b with e = 0.00848 (+0.00085
-0.00095). No long term radial acceleration was detected for any of the
targets. Combining all previous 20 measurements of beta and our six, we attempt
to statistically determine the distribution of the real spin-orbit angle psi
and find that between about 45 and 85 % of hot Jupiters have psi > 30 degrees.
Observations and predictions using the Kozai mechanism match well. If these
observational facts are confirmed in the future, we may then conclude that most
hot Jupiters are formed from a dynamical and tidal origin without the necessity
to use type I or II migration. At present, standard disc migration cannot
explain the observations without invoking at least another additional process.
