Reasonable belief
The standard required to authorize many police powers, such as obtaining a search warrant or arresting a person without a warrant. Reasonable belief as a standard to arrest requires that the arresting officer subjectively believe that the suspect has committed the offence and that objectively a reasonable person would reach the same conclusion. Reasonable grounds do not require as much evidence as a prima facie case but do require that the thing believed be more likely than not.
Source

Title: Criminal Procedure 3/e
By: Steve Coughlan