Unknown storage engine 'XtraDB'

Question

I installed Percona Server 5.6.12-rc60.4, when I want create table such as :

CREATE TABLE IF NOT EXISTS `mydb`.`table` (
`id` INT NOT NULL AUTO_INCREMENT ,
`title` VARCHAR( 64 ) NOT NULL ,
PRIMARY KEY ( `id` ) 
) ENGINE = XtraDB DEFAULT CHARACTER SET = utf8 COLLATE = utf8_unicode_ci;

this error occurred:

 #1286 - Unknown storage engine 'XtraDB' 

How can I create a table with XtraDB engine?