Since the input field is changed by slider, you can watch for events on the input field instead of needing to go through the slider plugin. Bind to the change event.
$( ".selector" ).bind( "change", function(event, ui) { ... });
The slider plugin has the following custom event:
create
This event is used to find out when a custom slider was created. It is not used to create a custom slider. The slider create event can be used like this:
$( ".selector" ).slider({ create: function(event, ui) { ... } });