Jquery CodeIgniter 2.X

Hello,

I have a mistake in my dev that i don' t understand.
I have a form which is link to a controler projet/formulaire

In this form i have an input text with an ID="ref".

I want to use

$('#ref").autocomplete({
source: "<?php site_url('projet/autocomplete') ?>
})

But when I type one cheracter in my input text nothing happen.
In public function projet/autocomplete i put a javascript alert and it doesn't appear.
I think that it don't go to the projet/autocomplete

Somebody have an idea.
Have a nice
Best