jq1.8.1

not working

HTML

<script src="http://code.jquery.com/jquery-1.8.1.min.js"></script>
<body>
    <div id="a">
        <div id="b">
        </div>
    </div>
</body>

CSS

#b{
    background-color: blue;
    height: 100px;
    width: 100px;
}

JavaScript

(function(){
    $("#a").on("click","#a #b",function(){alert("clicked")});
})();