You can use DAY_ONLY from the Date Functions in the where clause:

where DAY_ONLY(convertTimezone(CreatedDate)) > :dat

that combines...

You can use DAY_ONLY (not an obvious name for a function that pulls the Date part from a Datetime) from the Date Functions in the where clause:

where DAY_ONLY(convertTimezone(CreatedDate)) > :dat

combined with convertTimezone that deals with Converting Time Zones in Date Functions.

See my colleague's blog post on this subject Gotcha: convertTimezone() must be used in SOQL Date functions dealing with Datetime for more detail.