Alter $head_title_array so that it only passes 'Site Name' to '<TITLE>''

I'd like to be able to only display the 'Site Name' in the 'Title' bar. Currently it will display the page title with a separator and then the site name or if there is no page title it displays the site name, a separator and then the site slogan. Is there any way to control what goes into the $head_title_array?