Wordpress plugin

And I have included a action for it:
add_action( 'wp_ajax_the_ajax_hook_2', 'display_data_table' );

With the function that deals with database:
function display_data_table(){
$mno=$_POST['branch'];
//.. more code
}

Also my drop down menu html coding is:
<select name="branch" id="sel_branch" >
<option value="CSE">CSE</option>
// more options..
</select>

Now my jQuery script is like:
jQuery(document).ready(function(){
jQuery("#sel_branch").on('change', function(){
var dropdown_id=$(this).val();
jQuery.ajax({
type : "post",
url : the_ajax_script.ajaxurl,
data : {
action: "the_ajax_hook_2",
branch : dropdown_id
},
success: function(response_from_display_data_table) {
jQuery("#table_disp").html(response_from_display_data_table);
}
});
});
});