Example.com/foo redirect to example.com/foo/index.php

my config looks like:

server {
listen 443;
server_name foobar;

      access_log /var/log/nginx/https.access_log;
      error_log  /var/log/nginx/https.error_log debug;

      index           index.php index.html index.htm;
      fastcgi_index   index.php;
      root    /home/www/ssl/foobar;

      ssl on;
      ssl_certificate /etc/nginx/ssl/server.crt;
      ssl_certificate_key /etc/nginx/ssl/server.key;

      location ~ ^/mailadmin/(.*\.php)$ {
          fastcgi_index index.php;
          include /etc/nginx/fastcgi_params;
          fastcgi_param SCRIPT_FILENAME $request_filename;


a request tohttps://foobar/mailadmin/index.php is done very well and
the index.php is shown
a request tohttps://foobar/mailadmin/ is shown Error 403 Forbidden

How can i solve that a request tohttps://foobar/mailadmin/ is also
shown the index.php ?