I personally wouldn't worry too much about alt text for your logo since it is a background not an image file included on the page. Why not make the entire div clickable?
<div class="head" onclick="home();">
</div>
Then an external javascript file with this function
function home(){
window.location='http://www.homepage.com/';
}
The last thing you want to do is "rank" a transparent image with alt text or have text readers showing spacer images. This allows the entire div to be clickable.