Organic groups and Workflow
You create a workflow state called "review" and set it so it is only accessible by Head users. Also set the states so any author can only put workflows into this "review" state - only Head users can actually change this to other workflow states. 

So, the Head role can access the Workflow summary in order to review all the article group nodes which have been created in the review state.

If the Head approves it, he can change the workflow state to published which is accessible to all.

If the Head denies, he can change the workflow state to Needs work, which will mean the content remains unpublished.

If you want this to go back to the original author you can set this up with an email using actions / triggers or use the rules module.