Can a police officer detain me without arresting me?

Yes. If he has reasonable suspicions to believe you are committing a crime, a police officer can stop and detain you for a limited time to confirm or deny  his suspicions. If the officer has reasonable grounds to think you’re armed he may conduct a limited pat-down search of your outer clothing. Although the officer can question you, you have the right not to answer. But a refusal to identify yourself, may give the officer grounds to arrest you. Once the officer confirms or dispels his suspicions, he must either arrest you or let you go.