Private Security officers will begin patrolling downtown Santa Cruz this weekend as part of a pilot program to help boost security.   The program, which starts Saturday, includes 3 First Alarm security guards monitoring Pacific Avenue during the morning and early afternoon.  The officers, who won’t be authorized to carry guns, will be trained by Santa Cruz Police Department officers in municipal ordinances, and will utilize the police dispatch system to report problems as soon as they occur.  Police officials believe the new program will allow officers to concentrate on crime in other areas of the city.