I was accepted to UCR last week; like ammar, I received a fellowhip. This would lead me to believe that they sent their acceptances in waves. However, since their visit day is the 11th of April, I would assume all admitted students would be notified before then so that they could attend. If you haven't already, you might call the department and see what's up. Everyone I've spoken with there has been really helpful and very friendly.
Good luck!
Ammar, what do you think of the program? Have you talked with any of the professors? You can PM me if you want so that we don't hijack the thread.