I assume you are self-hosting FusionAuth, but let me know if this is not the case.
The database is the source of state in FusionAuth. So if you copied the database, then the same users and their logins should exist in that new copy. For how you have set up FusionAuth, I would expect your staging environment would have its own database as well as production.
When I click on http://staging.researchstudynline.com/ I see that the link is broken. You may want to review your configuration and ensure that you have properly set up the new FusionAuth instance (http://staging.researchstudynline.com:9011/) and its associated database.
I am linking the appropriate documentation which may aid you further in installing a new FusionAuth instance and database:https://fusionauth.io/docs/v1/tech/installation-guide/ https://fusionauth.io/docs/v1/tech/installation-guide/common-configuration/ https://fusionauth.io/docs/v1/tech/reference/configuration/
Lastly, there are a few different ways that you could replicate a database. One such way would be to use the pg_dump command. Once you have your dumped database, create a new empty database, and use pg_restore to import your data. Once you have your new database, you would stand up a new FusionAuth instance and point that instance at this new datastore. I would encourage you to use your search-fu to find articles that will speak to how to complete a database replication if you have any other questions about this process.
Hope this helps!