How to use XPath on xml docs having default namespace

I want to manipulate xml doc having default namespace but no prefix. Is there a way to use xpath without namespace uri just as if there is no namespace?
I believe it should be possible if we set namespaceAware property of documentBuilderFactory to false. But in my case it is not working.
Is my understanding is incorrect or I am doing some mistake in code?

Here is my code:

    DocumentBuilderFactory domFactory = DocumentBuilderFactory.newInstance();
    domFactory.setNamespaceAware(false);
    try {
        DocumentBuilder builder = domFactory.newDocumentBuilder();
        Document dDoc = builder.parse("E:/test.xml");

        XPath xPath = XPathFactory.newInstance().newXPath();
        NodeList nl = (NodeList) xPath.evaluate("//author", dDoc, XPathConstants.NODESET);
        System.out.println(nl.getLength());
    } catch (Exception e) {
        e.printStackTrace();
    }

Here is my xml:

<?xml version="1.0" encoding="UTF-8"?>
<root xmlns="http://www.mydomain.com/schema">
  <author>
    <book title="t1"/>
    <book title="t2"/>
  </author>
</root>